Holotype complete, with 84 segments, 30 mm long, 2 mm wide at chaetiger 15 (without chaetae). Paratypes incomplete, with 20–56 segments, 4–25 mm long, 0.8–1.0 mm wide. Colour in ethanol light brown. Prostomium slightly wider than long with a frontal cleft; two small frontal digitate antennae (Fig. 1A). Two pairs of eyes in trapezoidal arrangement, similar in size (Fig. 2A). Palps biarticulate, palpophore well developed, barrel-shaped, with subspherical palpostyles (Fig. 1A, Fig. 2A). Peristomium slightly longer than chaetiger 1, with four pairs of tentacular cirri, short, the longest postero-dorsally reaching to chaetiger 2 (Fig. 1A). Oral and maxillary pharyngeal rings without paragnaths or papillae; jaws brown, with 5 teeth on the dentate cutting edge. First two chaetigers sub-birramous; notopodia without aciculae, represented by a subulate dorsal ligule and short dorsal cirrus (Fig. 1B); neuropodia with subulate postchaetal lobe and ventral ligules and short ventral cirrus (Fig. 1C), only bearing homogomph spinigers (Fig. 2E-G). Birramous chaetigers from chaetiger 3 (Fig. 1D-I, Fig. 2B-D).

Figure 1.  

Nicon salinus Hernández-Acántara & Dávila-Jiménez, sp. nov. Paratype (CNAP-ICML: POP-39-005). A Anterior region, ventral view; B Chaetiger 1; C Notopodium of chaetiger 1; D Chaetigers 2, 3; E Chaetiger 4; F Notopodium of chaetiger 8; G Chaetiger 9; H Chaetiger 16; I Posterior chaetiger. Abbreviations: ch3, ch2 = chaetigers 2 and 3; dC = dorsal cirrus; dLi = dorsal ligule; mLi = median ligule; pLo = postchaetal lobule; vC = ventral cirrus; vLi = ventral ligule. Scale bars: 200 μm (A), 50 μm (B, D–I), 20 μm (C).

Figure 2.  

Nicon salinus Hernández-Acántara & Dávila-Jiménez, sp. nov. Holotype (CNAP-POH-39-003). A Anterior region, dorsal view. Additional material (CNAP-PO-39-034/2027); B Chaetiger 10; C Chaetiger 30; D Chaetiger 50. Paratype (CNAP-ICML: POP-39-005); E Homogomph spiniger of chaetiger 1; F Homogomph articulation of spiniger of chaetiger 2; G Homogomph spiniger of chaetiger 10; H-K Homogomph falcigers of chaetigers 12, 15, 25, 30; L Pygidium, ventral view. Abbreviations: dC = dorsal cirrus; dLi = dorsal ligule; mLi = median ligule; pLo = postchaetal lobule; vC = ventral cirrus; vLi = ventral ligule. Scale bars: 200 μm (A), 50 μm (B–D), 10 μm (E, H, J, K), 5 μm (F, I), 20 μm (G), 100 μm (L).

Anterior notopodia with short cirriform dorsal cirrus inserted at base of the triangular dorsal ligule; subulate median ligule; cirrus-like prechaetal lobe slightly shorter than the subulate median ligule (Fig. 1D–F, Fig. 2B); cirriform prechaetal lobe gradually smaller in middle chaetigers (Fig. 1D–H, Fig. 2C, D). Median and posterior notopodia with long, cirrus-like, dorsal ligule and short dorsal cirrus, inserted at base of ligule (Fig. 1H, I, Fig. 2C, D); median and posterior chaetigers with short prechaetal lobe, as a small process (Fig. 1H, Fig. 2C, D); near to pygidium, the dorsal ligule is shorter (Fig. 1I).

Anterior neuropodia with a short digitiform postchaetal lobe, projecting beyond end of the acicular ligule (Fig. 1G, Fig. 2B), a triangular ventral ligule and a short ventral cirrus (Fig. 2B). Median and posterior neuropodia with a short postchaetal lobe (Fig. 1C); subulate neuropodial ventral ligule, gradually smaller until entirely disappearing in posterior chaetigers; short ventral cirrus (Fig. 2D).

All notochaetae homogomph spinigers, with long, thin blades. Anterior neuropodia with homogomph spinigers, those in the supra- acicular ramus with long-blades and those from the infra-acicular ramus with short-blades (Fig. 2B, E–G). Median and posterior neuropodia with a supra-acicular ramus having long-bladed homogomph spinigers; infracicular ramus with homogomph spinigers superiorly and homogomph falcigers inferiorly, ending in a blunt curved tooth (Fig. 2H–K). Pygidium with broad margin and two long cirriform cirri, as long as last 7–8 segments (Fig. 1B).

Pharynx with two dentate jaws, without papillae or paragnaths. Anterior notopodia with triangular dorsal ligule and short cirriform dorsal cirri; subulate prechaetal lobe, similar in length to median ligule; median and posterior notopodia with dorsal ligule long, cirrus-like. Neuropodia with an acicular lobe and subulate neuroacicular ligule; triangular ventral ligule decreasing in size towards posterior chaetigers until entirely disappearing; short ventral cirrus. All notochaetae homogomph spinigers. Neuropodia with long and short-bladed homogomph spinigers and homogomph falcigers with blades ending in a blunt curved tooth.

The species name is derived from the Latin word “salinus”, meaning “salty” or “salted”, adjective used to highlight the hypersaline environment that this new nereidid inhabits, tolerating salinities up to 54.46 psu. Gender masculine.

Only known from type locality

Habitat: At 0.29–1.09 m depth, in fine sand and mud-sandy bottoms (50.08–78.67% sand). Temperature: 26.5–31.5°C; salinity: 34.30–54.46 psu; dissolved oxygen: 6.13–9.87 mg/l; pH: 7.97–8.39.

The genus Nicon has eleven valid species, including N. salinus sp. nov. (Read, G.; Fauchald, K. (Ed.) 2024), which can be separated into two large groups, according to presence or absence of notopodial prechaetal lobes (de León-González and Trovant 2013). The species group lacking notopodial prechaetal lobes includes N. ablepsia Wang et al., 2021 (Wang et al. 2021), N. abyssalis Hartman, 1967, N. maculatus Kinberg, 1865 (Kinberg 1865), N. moniloceras (Hartman, 1940) (Hartman 1940), N. pettibonae de León-González & Salazar-Vallejo, 2003 (de León-González and Salazar-Vallejo 2003) and N. yaquinae Fauchald, 1977 (Fauchald 1977) (Table 1).

On the other hand, the species group bearing notopodial prechaetal lobes includes N. salinus sp. nov. from the Gulf of Mexico, N. aestuarensis Knox, 1951 (Knox 1951) from New Zealand, N. japonicus Imajima, 1972 (Imajima 1972) from Ariake Sea, Japan, N. orensanzi de León-González & Trovant, 2013 from Bunche Beach, Ecuador and N. rotundus Hutchings & Reid, 1990 from Port Darwin, Australia. Nicon salinus sp. nov., with the anterior notopodial prechaetal lobes long, only slightly shorter than the median ligule and the neuropodia exclusively bearing homogomph spinigers and homogomph falcigers, can be clearly separated from N. aestuarensis, N. japonicus and N. rotundus, which have heterogomph falcigers and short notopodial dorsal ligules. In addition to heterogomph falcigers, N. rotundus also bears homogomph falcigers, whereas N. aestuarensis and N. japonicus bear heterogomph spinigers (Table 1).

In this group, Nicon orensanzi and N. salinus sp. nov. are the only species having long notopodial dorsal ligules, cirrus-like, on median and posterior parapodia. In N. orensanzi, the anterior notopodia have small triangular prechaetal lobes, which are absent in median and posterior notopodia and the neuropodia bear homogomph and heterogomph spinigers and sesquigomph falcigers. In contrast, the anterior notopodia in N. salinus sp. nov. have subulate prechaetal lobes, similar in length to the median ligules, absent in posterior chaetigers and the neuropodia only bear homogomph spinigers and homogomph falcigers (Table 1).

Previously, N. rotundus and N. abyssalis had been the only species of this genus having neuropodial homogomph falcigers, which were also observed in N. salinus sp. nov., but those species lack notopodial prechaetal lobes and, therefore, belong to the other Nicon species group (Table 1).

Sampling: The biological material was collected in February and May 2018 along the hypersaline Río Lagartos system, as part of the SALINITY GRADIENT ENERGY project of the Centro Mexicano de Innovación en Energía Océano (CEMIE Océano). It is an estuarine system located in the southern Gulf of Mexico (21°26' – 21°38'N; 87°30' – 88°05'W), belonging to the Ría Lagartos Biosphere Reserve. The samples were taken with a Ponar standard dredge (0.052 m²) and the sediments were sieved through a 500 μm mesh size to separate the macrofauna.

Preservation: The individuals were initially anaesthetised with magnesium chloride, fixed in 4% formaldehyde and later preserved in 70% ethanol (Dávila-Jiménez et al. 2019).

Morphological methods: The specimens of the new species were examined in detail to compare their morphological characteristics with those observed in close species: anterior, middle and posterior parapodia were dissected and mounted on glass slides to examine their morphological features and chaetal types. The scanning electron photographs were taken with a JEOL JSM6360LV microscope, the individuals were dehydrated via a graded ethanol series, critical-point dried with liquid CO₂ and coated with gold.

Terminology: To date, different terms have been given to name the nereidid parapodial structures, so, to standardise them we used the terminology for the atokous parapodial suggested by Villalobos-Guerrero and Bakken (2018) with some modifications made by Villalobos-Guerrero et al. (2021). However, due to the neuropodial lobes in the species of Nicon not being separable into superior and inferior lobes, the neuropodial lobe was named as the acicular lobe in accordance with Pettibone (1971) and Hutchings and Reid (1990), amongst others. The definition of types of articulation to the compound chaetae (homogomph, sesquigomph and heterogomph) suggested by Villalobos-Guerrero and Bakken (2018) was used to classify the observed homogomph falcigers in the new species.

Repository: The holotype and paratypes of the new species and the additional material examined were deposited in the "Colección Nacional de Anélidos Poliquetos" of the ICML, UNAM (CNAP-ICML: DFE.IN.061.0598).

Spinther n. sp.: Andrade et al. (2015): fig. 1E, tables 1, 2.

Spinther sp.: Tilic et al. (2022): fig. S2.

Holotype adult female with nine chaetigers, body 0.95 mm long, 0.63 mm wide at the widest point (excluding parapodia and chaetae). Paratype, possibly juvenile, with seven chaetigers (Fig. 3E). Body dorsoventrally flattened, oval. Live animals bright orange/red speckled with small white spots dorsally (Fig. 3A). Preserved specimens in alcohol white, with faint white spots visible on delicate fan-like notopodial lamellae (Fig. 3C). Notopodial fans covering the dorsum, except for the anteroposterior mid-line.

Figure 3.  

Spinther bohnorum Tilic & Rouse, sp. nov., live and preserved specimens. A, B Live images of S. bohnorum sp. nov.; A Dorsal view, showing the notopodial fans covering the dorsum, the small prostomium (pro) and the bright orange colouration speckled with white spots; B Ventral view; C, D Holotype (S. bohnorum, SIO BIC A18597); C Dorsal view; D Ventral view, with long, protruded proboscis (pb) visible in all specimens and oocytes (oo) apparent in the holotype; E Paratype (S. bohnorum, SMF 32994), ventral view, also showing a protruded proboscis. Scale bars: 250 µm.

Eyespots not visible. Prostomium small, spherical lobe situated dorsally between notopodial fans of chaetiger 2 (Fig. 3A). Mouth ventral, located posterior to chaetiger 1. Proboscis protruded, long (0.84 mm), with a mid-ventral groove and ventrally folded tip (Fig. 4A). Notopodia dorsally radiating, with thin, delicate lamellae between notochaetae (Fig. 3A, Fig. 4A). Most notochaetae bifid, with only a few entire ones irregularly distributed amongst them (Fig. 4G), all similar in thickness, distal parts of bifid notochaetae spread (Fig. 4C). Neuropodia cylindrical with slightly enlarged tips, without parapodial extensions (Fig. 4D). A single, compound neuropodial hook projects distally from each neuropodium. Neuropodial hooks strongly curved, with a prominent lateral tooth (Fig. 4F); 3-4 distally pointed aciculae embedded in neuropodia (Fig. 4D). Pygidium with two elliptical pygidial cirri (Fig. 4A).

Figure 4.  

Spinther bohnorum Tilic & Rouse, sp. nov., holotype (SIO BIC A18597). (A–D) CLSM images showing autofluorescence. A Overview of dorsal and ventral views. The chaetigers are numbered with Roman numerals and the pygidial cirri (pc) are shown in the ventral view; B, C Notochaetae, with inset highlighting the bifid distal ends with spread tips; D Neuropodium, showing internal aciculae (ac), a single protruding falcate compound hook and oocytes (oo); E Light microscopy (LM) image showing the protruded proboscis and oocytes; F Close-up of a compound neuropodial hook, with the lateral tooth marked by an arrow; G Detailed view of the distal ends of both bifid and entire notochaetae. Scale bars: 250 µm (A, E), 100 µm (B), 50 µm (C, D), 25 µm (F, G).

Spherical oocytes (diameter ±30 µm) visible through the body wall and attached to neuropodia (Fig. 3D, Fig. 4D, E).

Small species (ca. 1 mm) with bright red-orange colouration and white speckles dorsally. Ventral surface generally smooth. Neuropodia lacking parapodial extensions, with neurochaetae as falcate compound hooks bearing a marked lateral tooth. Notochaetae comprising both entire and bifid forms, with bifid chaetae having spread distal ends.

Spinther bohnorum sp. nov. is named after Brenda and Jeffrey Bohn and their family in appreciation of their steadfast support for marine invertebrate taxonomy and biodiversity research.

Known only from Mo'orea, French Polynesia.

Spinther is a small and easily recognised group of polychaetes, comprising only 12 accepted species reported worldwide, though half have been named from the North Pacific (Table 2). While the taxonomic history of Spinther is not extensive, it has been notably convoluted. Similarly, its phylogenetic affinities and placement within the annelid tree of life have long been a subject of debate (Rouse et al. 2022). Despite advances in molecular approaches, the placement of Spinther within the annelid tree of life remains unresolved. Andrade et al. (2015) included the transcriptome of Spinther bohnorum sp. nov. in their phylogenomic study, but their results were inconclusive, likely due to long-branch effects (see also Tilic et al. (2022)). Spinther is a monotypic genus, classified as Aciculata incertae sedis with uncertain affinities (Rouse et al. 2022), rendering the family name Spintheridae redundant.

Most Spinther species live on the surface of sponges, clinging to their hosts using their hooked neurochaetae. Their bright colouration often matches the sponge, providing camouflage. Whether Spinther is parasitic or a highly adapted commensal remains unclear. In the case of Spinther bohnorum sp. nov., it is also likely to associate with red sponges, given its colouration. However, this species was not collected directly on a sponge, but rather found in washings of coral rubble, suggesting a possible association yet to be confirmed.

Johnston (1845) introduced the name Spinther oniscoides Johnston, 1845 for specimens from Ireland. A few years later, Sars (1851), unaware of Johnston’s work, described Oniscosoma arcticus Sars, 1851 from northern Norway. Oniscosoma is now considered a junior synonym of Spinther (Sars 1862). Stimpson (1854), apparently unaware of both Johnston’s and Sars’ studies, described Cryptonota citrina Stimpson, 1854 from the Bay of Fundy, Canada, which was also later regarded as a junior synonym of Spinther (Sars 1862). Grube (1860) described S. miniaceus Grube, 1860 from the Adriatic Sea. Wirén (1883) subsequently used the name S. arcticus (Sars, 1851) for a species from the Bering Sea, considering it sufficiently similar to Sars’ species. However, Augener (1928), page 672, disputed this, asserting that Wirén’s specimen, collected during the Vega expedition, was distinct enough to warrant a new species. Augener proposed the name S. vegae Augener, 1928 for Wirén’s material, but only mentioned it in passing, without a formal description. Subsequently, Graff (1888) re-described the same specimen under the name S. arcticus. Augener criticised this approach, stating that it was inadmissible for Graff to retain the name S. arcticus for what he considered a different species. Despite this, S. vegae was never properly validated. Adding to the confusion, Hartman (1948) incorrectly interpreted Wirén (1883) as having created a homonym and replaced the name S. arcticus Wirén, 1883 with S. wireni Hartman, 1948. However, this replacement name was unnecessary and is now considered invalid. Riddell (1909) re-described S. oniscoides and highlighted that Graff had misidentified it, showing that Graff’s specimens actually belonged to S. citrinus. Levinsen (1883)'s Spinther major Levinsen, 1883 is also treated as a junior synonym of S. oniscoides by McIntosh (1900). Augener (1913) introduced S. australiensis Augener, 1913 from Western Australia. Hartman (1948) listed six species as valid within Spinther, including her new species, S. alaskensis Hartman, 1948. She treated S. miniaceus Grube, 1860 as a junior synonym of S. arcticus (Sars, 1851). In the western Pacific, S. hystrix Uschakov, 1950 was described from the Sea of Okhotsk, while S. japonicus Imajima & Hartman, 1964, S. ericinus Yamamoto, 1985 and S. sagamiensis Imajima, 2003 were described from Japan. Hartman (1967) also added S. usarpia Hartman, 1967 from the Antarctic. These contributions, alongside S. bohnorum sp. nov., bring the total number of nominal species to 15. A detailed and integrative investigation of Spinther species, combining morphological and molecular data, is needed to confirm or reject some of the proposed synonymies.

Spinther bohnorum sp. nov. most closely resembles S. australiensis in having falcate neurochaetae with a lateral tooth and no parapodial extension. However, S. bohnorum sp. nov. differs in possessing both bifid and entire notochaetae, whereas S. australiensis only has bifid notochaetae. Additionally, S. bohnorum sp. nov. exhibits a striking red-orange colouration with white speckles, while S. australiensis was originally described by Augener (1913) as “dull ochre-yellowish with whitish, colourless skin fans” (matt-ockergelblich mit weißlich farblosen Hautkämmen). Finally, S. bohnorum sp. nov. is much smaller, with the largest specimen having only 13 chaetigers and the mature female holotype having just nine chaetigers (± 1 mm body length), compared to S. australiensis, which was described with 23–31 chaetigers (> 4.5 mm body length).

The COI sequence obtained for a Spinther bohnorum sp. nov. specimen (USNM 1430143; GenBank: PV054334) matches the COI from the published transcriptome sequence (GenBank: PV053298) and was one of several generated as part of the Mo'orea Biocode project. The other two Spinther COI sequences generated (extractions catalogued as USNM 1430144; GenBank: PV054335 and USNM 143322) are arguably for different Spinther species, being 8–9% divergent from Spinther bohnorum sp. nov. and from each other. Unfortunately, there is no voucher material directly associated with these sequences. There are additional Spinther specimens collected as part of the Moorea Biocode project held at SIO-BIC and at the Florida Museum of Natural History, but the former were all fixed in formalin and those from the latter have not been sequenced. The presence of sympatric species of Spinther at Mo'orea warrants further investigation.

Specimens were obtained from coral rubble collected via SCUBA which was then treated with suspension-decantation and sieving. Live specimens were imaged using a LEICA MZ9.5 stereomicroscope with a CANON Rebel T1i camera. The formalin-fixed holotype was transferred from 70% ethanol to a 1:1 mixture of 99.5% undenatured ethanol and 98% glycerine prior to imaging. Over several days, the solution was gradually replaced by glycerine to allow a gentle transition from ethanol. This clearing step improves tissue transparency and enhances visualisation of chaetae for imaging. The specimen was photographed in dorsal and ventral views using a motorised NIKON SMZ25 stereomicroscope, equipped with a NIKON Digital Sight 10 camera, with image stacks processed using NIKON NIS Elements Basic Research software (v. 5.42.04). Confocal laser scanning microscopy (CLSM) scans were performed without staining (autofluorescence) using a LEICA DM2500 microscope, 405 nm excitation wavelength, a LEICA ACS APO 10× objective (dry) and LAS X (v. 3.5.7.23225) software. Image stacks were processed in Fiji (v. 1.54f). Distal ends of noto- and neurochaetae were imaged without differential interference contrast using a NIKON Eclipse Ni microscope at 40× magnification.

For molecular analyses, a COI sequence was obtained via Sanger sequencing for a Spinther bohnorum sp. nov. specimen (USNM 1430143) GenBank: PV054334, for which only the extraction remains. This was generated as part of the Moorea Biocode project (https://ocean.si.edu/ecosystems/coral-reefs/welcome-moorea-biocode-project).

The transcriptome assembly of Spinther bohnorum sp. nov. was used as a BLAST database. The Spinther COI sequence was used as a BLAST query to identify and mine the COI barcode sequence, which was subsequently uploaded to GenBank (accession number PV053298).

Specimen data for this description were (in parts) gathered and processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Repository: Type material are deposited at the Benthic Invertebrate Collection, Scripps Institution of Oceanography (SIO), Senckenberg Research Institute and Natural History Museum, Frankfurt (SMF) and Smithsonian National Museum of Natural History (USNM).

Body of small size (holotype: 16 x 10 mm, paratype: 13 x 8 mm), oval, carinated, moderately elevated (quotient of valve II = 0.31), side slopes slightly concave, valves solid, beaked. Tegmentum densely granulated, girdle expanded anteriorly (Fig. 5).

Figure 5.  

Craspedochiton zefranki Vončina, sp. nov. A, B Holotype MNHN-IM-2019-34865, dorsal and ventral view, respectively; C, D Paratype SMF 380885, dorsal and ventral view, respectively. Scale bar: 5 mm.

Tegmentum ground colouration yellowish, dark orange at the valves edges and jugum, with mostly white pustules and irregular small green maculation; girdle yellow to orange with irregular brownish patches and white blotches around the tufts (Figs 5, 6). Dorsum, despite well-defined jugum, hardly keeled, side slopes straight to slightly convex. Tegmentum densely covered with polymorphic pustules (Figs 6, 7A–E).

Figure 6.  

Craspedochiton zefranki Vončina, sp. nov., holotype MNHN-IM-2019-34865. A, C, E Valves I, II, VIII, respectively, dorsal view; B, D, F Valves I, II, VIII, respectively, ventral view; G, H Valve I, VIII, respectively, lateral view. Scale bar: 250 μm.

Figure 7.  

Craspedochiton zefranki Vončina, sp. nov., holotype MNHN-IM-2019-34865. A, C, E Valve I, II, VIII; B, D Details of tegmental surface of valve II in the anterior and posterior part of lateropleural area, respectively; F Central portion of radula. Scale bars: 2 mm (A, C, E), 500 µm (B, D), 200 µm (F).

Head valve semicircular with rather straight posterior margin, notched in the middle, with five elevated ribs consisting of irregular, elongate pustules, larger towards anterior and side margins of the valve, pustules between the ribs smaller, roundish in the apical region and larger, more elongate towards the margins (Fig. 6A, G, Fig. 7A). Intermediate valves roughly rectangular, weakly produced forward at jugal part, the posterior edge of the valve having a central protrusion that extends outwards, creating a small beak, flanked by straight edges on either side (Fig. 6C, Fig. 7C). Jugal area with wavy ridges, wedge-shaped, separated from the lateropleural areas. Lateropleural areas moderately elevated with an inconspicuous diagonal ridge consisting of slightly elevated and larger pustules, separating areas with different kind of granulation: anterior part covered with sparsely distributed, small and oval pustules (Fig. 6C, Fig. 7B, C) and posterior part with densely arranged, much larger and irregular pustules (Fig. 6C, Fig. 7C, D). Tail valve small, almost circular, slightly wider than long, with antemedian flat mucro, straight postmucronal slope; seven inequidistance elevated ribs formed by elevated large pustules correspond to the articulamentum slits; granulation of the tail valve similar to the intermediate valves, with the antemucronal area covered with small oval pustules and the postmucronal area with densely distributed, much larger and elongate pustules (Fig. 6E, H, Fig. 7E).

Articulamentum strongly developed, creamy-pink, but white in apophyses and under the pleural areas of the intermediate valves. Slit formula: 5/1/7. Slits deep and wide, smooth, but with distinct dorsal grooves; insertion plates long and wide. Apophyses well-developed, rounded in a head valve, trapezoidal in valve II and very short, but wide, rectangular with rounded edges in tail valve (Fig. 6B, D, F).

Girdle anteriorly expanded, light orange with irregular brownish patches and white blotches around the tufts. Dorsally densely covered with short, flattened spicules, with distinct radial ribs in their upper half – ribs usually not reaching the tip which tends to be tapered and smooth, L: 56–62 μm (mean = 58 μm, n = 10), W: 10–15 μm (mean = 12 μm, n = 10), intermingled with long, randomly, but densely distributed hair-like, smooth long spicules, usually bent, L: 210–420 μm (mean = 318 μm, n = 3), W: 33–42 μm (mean = 37 μm, n = 3) (Fig. 8A–C); 18 sutural tufts indistinct, consisting of very short (likely broken), thick, straight spicules. Marginal fringe of elongate, rounded, straight and point-ended spicules (some spicules striated), L: 322–347 μm (mean = 340 μm, n = 3), W: 37–50 μm (mean = 42 μm, n = 3) (Fig. 8D). Ventral spicules densely arranged, tiled, polymorphic, very elongate to oval with a clear zonation. The anterior and middle part of hyponotum covered with longitudinally densely striated, flattened scale-like spicules, L: 75–120 μm (mean = 87.6 μm, n = 7), W: 40–75 μm (mean = 53.4 μm, n = 7) (Fig. 9A). The posterior part of hyponotum covered with elongate, flattened, sharply pointed or slightly tapered and deeply striated spicules, L: 170 μm, W: 30 μm, n = 1, (Fig. 9B). Mantle fold with smooth, flat, elongated scales at the edges (L: 800 μm, W: 200 μm, n=1) and very long, straight, deeply striated spicules, L: 451–553 μm (mean = 499 μm, n = 8), W: 21–44 μm (mean = 32.5 μm, n = 8), intermingled with similar, but much shorter spicules (up to 250 μm), more abundant closer to the interior part of the mantle fold (Fig. 9C–F).

Figure 8.  

Craspedochiton zefranki Vončina, sp. nov., holotype MNHN-IM-2019-34865. A, B Dorsal girdle spicules from the anterior part of perinotum; C Dorsal girdle spicules and hair from the anterior part of perinotum; D Marginal spicules. Scale bars: (1) 200 µm (A), 100 µm (B), 300 µm (C, D).

Figure 9.  

Craspedochiton zefranki Vončina, sp. nov., holotype MNHN-IM-2019-34865. A–F Ventral spicules. A Spicules of the central part of hyponotum; B Spicules of the posterior part of hyponotum; C Single spicule from the anterior part of the mantle fold; D, E Spicules from the central part of the mantle fold; F Spicules from the posterior part of the mantle fold. Scale bars: 300 µm (A, B) 400 µm (C), 200 µm (D, E, F).

Radula of holotype small, ca. 3 mm in length, with 46 rows of teeth, of which 40 are matured. Central tooth subrectangular, the apical edge is very thin and folded, which gives it a bicuspid look, with wide base and tapering towards the top, the antero-lateral corner of the centro-lateral tooth is obtuse and smooth, thin. First lateral tooth elongate, major lateral tooth robust, with tricuspid head, denticles pointed, of similar size (Fig. 7F).

Gills merobranchial, six ctenidia per side.

Chitons of small size, up to 15 mm, body oval, girdle expanded anteriorly; colour of the tegmentum yellowish, mottled with dark orange and green; girdle yellow to orange with brownish maculation and white patches around the tufts. Valves carinated, moderately elevated, densely covered with pustules. Head valve with five distinct ribs, tail valve almost circular, mucro antemedian, flat. Perinotum covered with short, ribbed spicules and scattered with hair-like long spicules; hyponotum covered with scale-like, deeply striated spicules and very long thin spicules on the mantle fold.

The specific epithet zefranki is a masculine adjective formed from the name of Hosea Jan "Ze” Frank, an online performance artist known for his wit, creativity and humorous approach to scientific knowledge in the YouTube series TRUE FACTS. The name honours his influential contributions to internet culture and the vision he has brought to the SENCKENBERG OCEAN SPECIES ALLIANCE as a member of its advisory board.

At present known only from its type locality, the Solomon Islands.

Morphological discussion

The genus Craspedochiton consists of 14 currently accepted species and five of them belong to Thaumastochiton-group Thiele, 1909 (Schwabe and Els 2019) which is characterised by the uplifted posterior mucro and unslitted callus in the tail valve. As Craspedochiton zefranki sp. nov. has antemedian positioned mucro, it surely does not belong to this group. The new species can be immediately distinguished from the rest of the species belonging to the same genus by its roundish insertion plates in the head valve (in all other species they are rectangular). Additionally, below there are provided more detailed differences between the new species and other Craspedochiton reported from the similar geographic range. C. zefranki sp. nov. differs from:

Craspedochiton elegans (Iredale & Hull, 1925) by sculpture of the valves (small, fine pustules in C. elegans vs. much larger, coarser pustules in C. zefranki sp. nov.), by the shape of the tail valve (rhomboidal in C. elegans vs. roundish in C. zefranki sp. nov.), position of the mucro (in posterior third and elevated in C. elegans vs. antemedian and flat mucro in C. zefranki sp. nov.);

Craspedochiton hystricosus Kaas, 1991 by the sculpture of the valves (much finer, smaller pustules, roundish or elongate vs. much larger, irregular, but squarish in C. zefranki sp. nov.), longitudinal ridges in the pleural area of the intermediate valves (present in C. hystricosus vs. absent in C. zefranki sp. nov.), position of mucro (more posteriorly located in C. hystricosus vs. antemedian in C. zefranki sp. nov.), ridges on the head valves (only weakly indicated in C. hystricosus vs. conspicuous in C. zefranki sp. nov.);

Craspedochiton jaubertensis Ashby, 1924 by the sculpture of the valves (much larger, solid pustules in C. jaubertensis vs. smaller, less coarse pustules in C. zefranki sp. nov.), the shape of the valves (median trapezoidal in C. jaubertensis vs. rectangular in C. zefranki sp. nov.), position of mucro (more central in C. jaubertensis vs. more anteriorly located in C. zefranki sp. nov.), apophyses in tail valve (longer, more produced forward in C. jaubertensis vs. shorter, reaching the postmucronal areas in C. zefranki sp. nov.);

Craspedochiton laqueatus (G. B. Sowerby II, 1842; Dell’Angelo et al. (2010) – illustrations of type material) by the sculpture (larger, coarser pustules, especially in the pleural areas of intermediate valves in C. laqueatus vs. smaller, more densely arranged pustules, rounded and small in pleural areas of intermediate valves in C. zefranki sp. nov.), by the shape of the second valve (convex anterior edge, protruding beak flanked by concave posterior edges in C. laqueatus vs. almost straight, slightly protruding at jugal part and a small beak flanked by straight posterior edges in C. zefranki sp. nov.), morphology of hyponotum scales (less numerous striae in C. laqueatus vs. much more numerous striae in C. zefranki sp. nov.);

Craspedochiton tesselatus Nierstrasz, 1905 by the shape of the apophyses in the head valve (rectangular in C. tesselatus vs. roundish in C. zefranki sp. nov.), position of mucro and postmucronal slope (median mucro and strongly concave slope in C. tesselatus vs. antemedian mucro and straight slope in C. zefranki sp. nov.).

Molecular discussion

The obtained sequence was positively checked as belonging to Polyplacophora against the GenBank database; however, with only ca. 86% similarity to published sequences. The closest relative in GenBank was Acanthochitona ferreirai W. G. Lyons, 1988 (86.02% similarity, acc. No. MK016365.1). The number of publicly available sequences of Craspedochiton is relatively low (2 COI sequences belonging to two species). A phylogenetic analysis which could explain low similarity to the other sequences from the same genus was not conducted; the COI barcode of the new species is provided for future use.

Live animals were collected at depths of 97–223 m by the French expedition SOLOMON 1 at Station DW1840 near the Solomon Islands. Specimens were fixed in 100% ethanol. The systematic classification follows Sirenko (2006), the morphological nomenclature following Schwabe (2010).

For scanning electron microscopy (SEM), the valves and radula were removed, cleaned with a diluted bleach solution (1:1 with H₂O) and rinsed in distilled water. Several small pieces of dorsal and ventral girdle were sampled, as the spicules tend to be highly polymorphic at intra-individual level, following Schwabe and Els (2019) recommendations. Girdle tissue was only air dried. Objects were placed on SEM stubs using double-sided adhesive tabs. Samples were examined with a HITACHI TM4000 tabletop SEM. After SEM examination, spicules which best represented variability of the species girdle were presented in the figures. All figures were assembled in Adobe Photoshop.

For DNA barcoding, a small fragment of tissue from the holotype’s foot was sampled. DNA was extracted using QIAamp DNA Micro Kit (QIAGEN), following the manufacturer’s protocol. The cytochrome oxidase subunit I (COI primers LCO1490 and HCO2198; Folmer et al. (1994)) was amplified using TaKaRa Taq HS Perfect Mix from TaKaRa. The PCR conditions involved an initial denaturation step at 94ºC for 5 minutes; then 35 cycles of denaturation at 94ºC for 45 seconds, annealing at 50ºC for 45 seconds and extension at 72°C for 1 minute and 30 seconds; followed by a final extension step at 72°C for 5 minutes. The obtained sequence was manually inspected and trimmed to the length 612 bp in Geneious Prime v.2023.1 and was made publicly available on GenBank under accession number PV664593.

Specimen data for this description were (in parts) processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Abbreviations used in the text are as follows: Muséum National d'Histoire Naturelle, Paris, France (MNHN); Senckenberg Research Institute and Natural History Museum Frankfurt (SMF).

Repository: Holotype (MNHN-IM-2019-34865) is now deposited in the collection of MNHN; one paratype (SMF 380885, old MNHN number: MNHN-IM-2019-35217) is deposited in the malacological collection of SMF.

Holotype 18.0 × 8.5 mm, oval. Overall colour of valves light brown, frequently marked with scratches revealing white shell.

Valves rounded, little elevated (dorsal elevation ratio 0.28 in valve III, Fig. 10A). Head valve semicircular. Intermediate valves slightly recurved, lateral margins rounded, anterior margin concave, posterior margin paralleling anterior margin, apex not projecting. Lateral areas not raised or visibly demarcated. Tail valve as wide as head valve, flattened, mucro central, posterior slope flat (Fig. 10A, B). Tegmentum smooth, covered with tissue and apical projections from aesthete pores. Aesthetes in bundles of one megalaesthete and approximately six micraesthetes with caps protruding from aesthete openings (Fig. 11A, C). Aesthete bundles typically in two parallel rows of three micraesthetes, but often irregularly arranged (sometimes 5 or 7 per megalaesthete).

Figure 10.  

Ferreiraella charazata Sigwart, sp. nov. A Holotype SCSMBC240287, valves. From top to bottom: valve I, valve III (anterior view), valve V, valve VIII and valve VIII in lateral view; B Paratype 1 SMF 380825; C In situ photograph of multiple specimens (indicated with arrowheads) on sunken wood, together with other fauna. Scale bars: 2 mm.

Figure 11.  

Ferreiraella charazata Sigwart, sp. nov., holotype SCSMBC240287, SEM micrographs. A Aesthete pores, shown from valve I; B Radula; C Aesthete caps, shown from valve IV; D–F Girdle scales (perinotum). All scale bars: 100 μm (A, B, D–F), 25 μm (C).

Articulamentum white, well developed, without insertion plate or callus, apophyses moderately narrow, triangular in the intermediate valves and tail valve. Jugal sinus wide and convex.

Central tooth of radula small, bud-like, first (inner) lateral teeth with brush-like projections. Second (major) lateral teeth with flattened, tridentate mineralised cusps. Third uncinal (sweeper) teeth with extremely large and broad, spoon-shaped, but comb-like blade (Fig. 11B).

Girdle very wide, dorsally densely covered with oblong spicule-scales (up to 80–100 × 15–20 μm). Scales are proximally smooth, suboval in cross section, but include two types: distally tapering to a blunt point or distally stellate with four or six ribs. Ventral side of girdle naked.

Gills 11 on each side (paratype 3), smaller to the anterior, extending from valve VI to the anus.

Animal medium, holotype approximately 18.0 mm long (estimated from curled position). Overall colour brown, frequently marked with scratches revealing white shell. Shell rounded, valves not beaked, mucro of tail valve slightly anterior, tail valve flattened. Tegmentum smooth; aesthetes in bundles of one megalaesthete and six micraesthetes, with protruding caps. Girdle densely covered with oblong spicule-scales, flattened oval in profile. Scales include two types: distally bluntly pointed or stellate. Major lateral teeth of radula with relatively flattened, tridentate cusps. Sweeper teeth large, expanded, comb-like. Eleven gills on each side.

From the Latin charazo meaning scratch or engrave, noting the common white scratch marks on the brown dorsal shells in this species (adjective, feminine).

Only known from the type locality.

Sigwart and Sirenko (2012) provided a dichotomous key to all species of the genus Ferreiraella. The new species has a tail valve most similar to F. plana. In geographic range, F. charazata sp. nov. could be most comparable to F. tsuchidai Saito 2006, but the intermediate valves are oval in F. tsuchidai and cardioid in F. charazata sp. nov. The tail valve in F. tsuchidai is more oval with a straight postmucronal slope, round in F. plana and, in F. charazata sp. nov., the tail valve is distinctly triangular and the postmucronal area very flat. Specimens of F. charazata sp. nov. and F. tsuchidai frequently host epibiotic tubeworms on their tail valves.

Individuals of F. charazata sp. nov. were collected in 2018 from sunken wood by remotely operated vehicle (ROV) ROPOS aboard R/V TAN KAH KEE, in the framework of the research programme “Deep Sea Process and Evolution of the South China Sea”.

Specimens were photographed using a motorised NIKON SMZ25 stereomicroscope, equipped with a NIKON Digital Sight 10 camera and stacked with NIKON NIS Elements Basic Research software (v. 5.42.04). Body size was measured from these photographs using ImageJ software (v.1.54g); to estimate body length in curled specimens, a curved line was fitted along the perinotum-plate boundary of lateral-view images and subsequently digitally straightened.

The holotype SCSMBC240287 was dissected to remove head, tail and representative intermediate valves, the radula and a piece of the perinotum for spicule preparation. Small cuts of the radula and girdle, as well as a fragment of the head valve were cleaned of soft tissue using diluted (max. 50%) household bleach for a few minutes, carefully rinsed with fresh water and transferred to aluminium SEM stubs with double-sided adhesive carbon tabs, either via air drying (valve fragment, spicules) or following dehydration through a graded ethanol series and subsequent chemical drying by means of hexamethyldisilazane (radula). SEM images were taken with a HITACHI TM4000Plus Tabletop scanning electron microscope with (chemically-dried radula) and without (other preparations) gold-palladium coating.

Spicules were measured using scales on SEM images and ImageJ. Images were processed with Adobe Photoshop 2024.

Specimen data for this description were gathered and processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Repository: Specimens are housed in the South China Sea Marine Biological Collections, Chinese Academy of Sciences, Guangzhou, China (SCSMBC) and the Senckenberg Research Institute and Natural History Museum Frankfurt (SMF).

Chitons of small to medium size with body length up to 19 mm, elongate-oval, valves moderately elevated (dorsal elevation about 0.35). Head valve slightly narrower than tail valve. Valves V and VI widest. Tail valve with anterior mucro. Ratio of length of postmucronal area to length of antemucronal area 1.4. Tegmentum sculptured with small elongated granules closely arranged in longitudinal rows in central areas of intermediate valves and in antemucronal areas of tail valve and in quincunx patterns or in a random manner in other areas. Most granules with 1, 2 or 3 aesthete pores. Perinotum narrow, 5.5 times narrower than valve V, covered with bluntly pointed, slightly flattened, long spicules with 10–12 vague longitudinal ribs around spicule. Marginal needles and ventral spicules with vague longitudinal ribs or smooth. Radula ca. 5 mm long, with about 126 rows of mature teeth; central tooth large and unusual wide, with round dorsal edge, first lateral tooth narrow, roughly L-shaped, major lateral teeth large, with flat elongate heads, first uncinal tooth unusually narrow and elongated, major uncinal tooth long with well-developed blade. Number of gills in adult specimens 22.

The genus name is a combination of the Greek roots pycno- (dense), dont- (tooth) and chiton, referring to the distinct dense tooth rows of the radula in this genus. The Greek word χιτών (chiton) is a masculine noun in the third declension.

Deep-water chemosynthetic habitats from the East China Sea to the South China Sea.

The new genus includes two species: Pycnodontochiton tenuidontus (Saito and Okutani, 1990) comb. nov., found in hydrothermal vent sites in the Okinawa Trough area and P. sinensis gen. et sp. nov., from the Haima cold seep area in the South China Sea, at depths of 1385–1392 m.

Although new genus is superficially similar to Leptochiton as considered by Saito and Okutani (1990), it differs significantly from all known species in the teeth of the radula. Really no species of chitons, including species of the genus Leptochiton, have such huge central teeth and such long first uncinal tooth, which undoubtedly confirms the validity of the new genus Pycnodontochiton gen. nov.

Holotype (body length 17.0 mm) elongate oval, valves subcarinated, moderately elevated (dorsal elevation 0.35), not beaked, side slope slightly convex, apex damaged, tegmentum white in colour.

Head valve semicircular, hind margin with notch; intermediate valves rectangular, valves V and VI widest, anterior margin convex in valve II and concave in other intermediate valves, posterior margin slightly convex, lateral area weakly raised; tail valve is 1.1 times wider than head valve, mucro anterior, postmucronal slope first concave then convex, antemucronal area convex (Fig. 12 A, B).

Figure 12.  

Pycnodontochiton sinensis Sirenko, Zhang & Sigwart, sp. nov. A Holotype MBM229047, valves. From top to bottom: valve I (ventral view), valve I (dorsal view), valve III, valve VIII; SEM image on lower right: valve VIII in lateral view; B Paratype 1 MBM229048, lateral view; C Paratype 3 SCSMBC240288, Schwabe organ (dark region, adjacent to mouth). Scale bars: 2 mm (A, B), 0.25 mm (C).

Tegmentum sculptured with small elongated granules (160–200 x 60–70 µm) closely arranged in longitudinal rows in central areas of intermediate valves and in antemucronal areas of tail valve and in quincunx patterns or in a random manner in other areas. Each granule with one aesthete or sometimes two aesthetes, irregularly placed within low granules (Fig. 13A, C). Head valve, lateral areas of intermediate valves and postmucronal area of tail valve with 5–6 concentric terraced growth rings.

Figure 13.  

Pycnodontochiton sinensis Sirenko, Zhang & Sigwart, sp. nov., SEM micrographs. A Paratype 2 SMF 380828, aesthete pores, shown from valve III; B–E Holotype MBM229047, radula (B), aesthete pores (C), girdle scales showing marginal scales (D), radula at a different position on the radular ribbon, showing the unusually large first uncinal (arrowheads; E); F, G Paratype 2 SMF 380828, ventral girdle scales (F), dorsal girdle scales (G). Scale bars: 100 μm (A, C, D, F, G), 500 μm (B, E).

Articulamentum well developed, white, apophyses small, widely separated from each other, more or less triangular in intermediate valves or trapezoidal in tail valve. Ratio of width of jugal sinus to width of apophyses 1.3.

Girdle at valve V, 5.5 times narrower than valve width, dorsally covered with bluntly pointed, slightly flattened, long spicules (160 x 50 µm) with 10–12 vague longitudinal ribs around spicule. Marginal needles (200–210 µm) and ventral spicules (100–110 x 20–30 µm) also with vague longitudinal ribs, slightly square in cross section (Fig. 13D, F, G).

Holotype with gills extending from valve V to near anus. Paratype 1 with 19 gills on each side (actual number 17, estimated 19 due to defect), paratype 2 with 22 gills.

Radula 5 mm long, with 126 transverse rows of mature teeth, central tooth large and unusually wide (over 130 µm), with round dorsal edge; first lateral tooth narrow, roughly L-shaped, with a small blade; major lateral teeth large, with bidentate heads; first uncinal tooth unusually narrowly elongated, major uncinal tooth long with well-developed blade (Fig. 13B, E).

Width of valves (holotype): I-8.0 mm, II-9.2 mm, III-10.0 mm, IV-10.9 mm, V-11 mm, VI-11.0 mm, VII-10.2 mm, VIII-8.9 mm. Schwabe organ large, dark brown-black (Fig. 12C).

As for genus.

Named for its occurrence off the coast of China.

Only known from the type locality.

As already noted, P. sinensis gen. et sp. nov. is closely related to the congener P. tenuidontus. Pycnodontochiton sinensis gen. et sp. nov. differs from P. tenuidontus in having an even wider central tooth of radula and without its narrowing in distal part and having bidentate heads of the major lateral teeth and also by its ribbed marginal needles and by ribbed ventral spiculae. The new species is distinguished from all other species of chitons by the remarkably long and flat central tooth of radula and an unusually long first uncinal tooth.

The radula of P. sinensis gen. et sp. nov. is its most distinctive feature. Pycnodontochiton tenuidontus, from hydrothermal areas, has a similar radula that was described as unique because of its flat, overlapping teeth (Saito and Okutani 1990), similar to P. sinensis gen. et sp. nov. and both species have indistinct granular sculpture. The radula of P. tenuidontus also has a prominent, wide and round central tooth and a distinctive inner small lateral (between the major lateral and sweeper teeth), two features that are absent in P. sinensis gen. et sp. nov. Pycnodontochiton tenuidontus has three aesthetes in a bundle on each granule, but P. sinensis gen. et sp. nov. has one or two aesthetes per granule. The valves in P. tenuidontus are also round-backed, compared to subcarinate in P. sinensis gen. et sp. nov. Two other species with densely-packed, flat-headed major lateral teeth in the radula are Leptochiton kerguelensis (Haddon, 1886), from Antarctic and sub-Antarctic regions and Leptochiton ferreirai Sirenko & Sellanes, 2016 from deep water near Chile. Both those species are much smaller in body size than Pycnodontochiton spp. and live in distant regions and other features of the radula differ. The radula of L. kerguelensis has large, broad sweeper teeth not like the elongate first uncinal seen in P. sinensis gen. et sp. nov. The major lateral teeth in the radula of L. ferreirai are distinctly tricuspid and pointed, not square and bicuspid as in P. sinensis gen. et sp. nov.

Paratypes SMF 380828 and SCSMBC240288 were prepared as described for Ferreiraella charazata Sigwart, nov. sp., but all preprations for SEM imaging were air dried directly on the stubs and observed without metal coating.

For DNA barcoding, a small fragment of tissue from the foot of paratype 3 was sampled and amplification and sequencing were performed using the primer sets LCO1490/HCO2198 (Folmer et al. 1994).

Specimen data for this description were (in parts) gathered and processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Repository: Specimens are housed in the Marine Biological Museum, Chinese Academy of Sciences, Qingdao, China (MBM), the South China Sea Marine Biological Collections, Chinese Academy of Sciences, Guangzhou, China (SCSMBC) and the Senckenberg Research Institute and Natural History Museum Frankfurt (SMF).

Veleropilina cf. oligotropha (Rokop, 1972): Brandt (2022): 157, 165, Fig. 5.96, tab. 5.26

Veleropilina sp. Sigwart et al. (2025): table 1, fig. 4B

Veleropilina sp. Chen et al. (2025): fig. 1, text

Animal relatively large for the genus (5.2 mm long, 4.0 mm wide, 2.0 mm high), width to length ratio 0.77, height to length ratio 0.38 (Fig. 14A–C). Shell fragile, pale, translucent, whitish. Aperture ovoid, evenly rounded posteriorly, slightly narrowing anteriorly. Apex protruding beyond anterior shell margin, but forming a regularly curved arc with dorsal teleoconch surface in lateral view. Apical cap approximately 280 μm long, 250 μm wide, positioned at an angle of slightly more than 100° relative to the ventral plane, eroded in the holotype, smooth except for six closely-spaced concentric ridges at transition to teleoconch (Fig. 14F, arrowheads). Shell surface ornamented with prominent reticulate sculpture comprised of numerous concentric ribs with irregular interspacing, but becoming slightly closer together distally. Radial ribs slightly thinner and less prominent than the concentric sculpture, spaced more closely at posterior, with broader interspacing at anterior. Rib intersections with weak nodes (Fig. 14E, G), delimiting rectangular interspaces of variable size.

Figure 14.  

Veleropilina gretchenae Sigwart & Steger, sp. nov., holotype SMF 373808. A Ventral view (line indicates approximate location of x-ray virtual cross section shown in image D); B Dorsal view; C Lateral view (right side); D Virtual cross section from synchrotron x-ray micro-CT, with arrowhead indicating position of radula; E Detail of teleoconch sculpture; F Apical cap, with arrowheads indicating the position of concentric ridges marking the transition to the reticulate teleoconch; G Detail of teleoconch sculpture showing minor irregularity. Scale bars: 1 mm (C–D), 100 μm (E–G).

Foot prominent, subcircular, surrounded by a wide, shallow pallial groove; five digitate gills per side, each approximately as long as the width of the pallial groove in the preserved specimen. Anterior velar lobes large, elongated, leaf-like, almost three times as long as the diameter of the anterior lip. Postoral tentacles well-developed. Radula docoglossan with one pair of prominent major teeth (visible in micro-CT; Fig. 14D); radula cartilages large. Eight dorso-ventral muscles per side, first pair (counting from anterior) immediately posterior to radula cartilages; second pair divided into two distinct bundles of inequal size (anterior part smaller). Gut with six loops.

Large-sized Veleropilina (shell length > 5 mm); shell moderately elevated (height to length ratio 0.38), surface covered by prominent reticulate sculpture with almost equally thick radial and concentric ribs delimiting rectangular to squarish interspaces. Aperture ovoid, narrowing anteriorly. Apex protruding beyond anterior shell margin, forming a regularly curved arc with the dorsal teleoconch surface when viewed laterally. Apical cap large, approximately 280 μm long and 250 μm wide, positioned at an angle of slightly more than 100° relative to the ventral plane. Postoral tentacles and velar lobes well-developed, the latter more than three times longer than the diameter of the anterior lip. COI mitochondrial barcode region with 12.71% difference (87.29% BLAST similarity) to that recovered from the V. oligotropha (s.l.) genome of Chen et al. (2025) and 7.23% difference (92.77% similarity) to another previously published COI sequence of V. oligotropha (NCBI accession MF157522, Wiklund et al. (2017)) in a smaller region of sequence overlap.

Named after Dr Gretchen Van Meer Sigwart, civil engineer and professor, in recognition for her pioneering accomplishments and advocacy for equality and support for women in science, LGBTQ rights and people with disabilities.

Only known from the type locality.

The new species differs from other congeners in several respects. Previously published analyses of the genome of Veleropilina gretchenae sp. nov. (sequenced from the holotype, as Veleropilina sp.) and a specimen identified as V. oligotropha (Rokop, 1972) revealed significant differences with an estimated divergence time of 72 million years (Chen et al. 2025). This substantial separation sheds new light on the importance of apparently minor morphological differences. Amongst these, the most obvious are body size, apertural shape and lateral shell profile: V. gretchenae sp. nov. is considerably larger than V. oligotropha and has an aperture that narrows anteriorly; its apical cap is well-aligned with the dorsal teleconch surface located behind it, forming a smooth, regularly curved arc, whereas it represents a prominent, growth stage-independent discontinuity or bump in V. oligotropha. In size, proportions of the shell and dimensions of the apical cap, V. gretchenae sp. nov. is most similar to V. zografi (Dautzenberg & H. Fischer, 1896) from the North Atlantic Ocean, but differs in the sculpture (relatively broad and low-profile, very narrowly-spaced concentric ribs in V. zografi) as well as geography (Warén and Gofas 1996). The radula of V. gretchenae sp. nov. as visible in micro-CT appears to be structurally similar to Veleropilina seisuimaruae Kano et al., 2012, although this is not entirely clear from the available data; as the holotype of the former species was badly damaged due to tissue sampling for genomic analysis, we elected not to pursue further dissection. All previously described species in Veleropilina, except V. oligotropha, occur at much shallower depths (Kano et al. 2012). Veleropilina gretchenae sp. nov. can most usefully be compared to other species in the genus reported from the Pacific (Table 3), highlighting the distinctive characters of V. gretchenae sp. nov.: larger size, relatively tall shell and large apical cap.

The holotype of V. gretchenae sp. nov. was collected during the SO293 AleutBio expedition of German R/V SONNE in 2022, using a 3.5 m-wide Agassiz trawl with 10 mm cod end mesh size (OKTOPUS GmbH). Contents of the net were sieved on a 1 mm mesh and subsequently preserved in 96% ethanol (Brandt 2022).

Photographs of the intact specimen were taken on board, prior to tissue sampling for genome sequencing (methods described in Chen et al. (2025), Electronic Supplementary Materials).

To molecularly compare the new species with the morphologically similar congener V. oligotropha (Rokop, 1972), both species’ COI sequences were extracted from published genomic datasets (Chen et al. (2025), with V. gretchenae sp. nov. reported as V. sp.); a further COI sequence of V. oligotropha from the Clarion-Clipperton Zone was downloaded from GenBank (accession no. MF157522; Wiklund et al. (2017)). Sequence similarity between V. gretchenae sp. nov. was assessed using NCBI BLAST (Camacho et al. 2009). The COI sequence isolated from the genome of V. gretchenae sp. nov. for the purpose of this study was uploaded to the Barcode of Life Data Systems (BOLD) (see Materials section for details).

Shell microsculpture and apical cap morphology was investigated and documented, based on shell fragments (produced by invasive tissue sampling) after air drying them, using a HITACHI TM4000Plus Tabletop scanning electron microscope (SEM) without metal coating.

Soft body anatomy was studied from a micro-computed tomography (micro-CT or µCT) scan performed at the ANATOMIX beamline, synchrotron SOLEIL, Paris, following the methods and settings described in Ampuero and Sigwart (in press). Prior to CT scanning, the specimen was incubated in a contrasting solution of 0.3% phosphotungstic acid and 3% dimethyl sulphoxide in 95% ethanol (Senckenberg Ocean Species Alliance (SOSA) et al. 2024) for ca. 1 week. The x-ray virtual section shown was produced with Dragonfly software (v. 2022.2; OBJECT RESEARCH SYSTEMS).

Shell measurements (length, width, height) were taken from habitus images of the intact specimen using NIKON NIS Elements Basic Research software (v. 5.42.04). Apical cap size was determined from SEM images using TM4000 software (HITACHI Ltd, Tokyo, Japan).

Image processing and figure plate assembly was performed in Adobe Photoshop 2025.

Specimen data for this description were gathered and processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Repository: The holotype is housed at the Senckenberg Research Institute and Natural History Museum Frankfurt (SMF).

Laevidentalium wiesei n. spec.: Sahlmann (2012): 26, Plate 6, figs. 1–3; 27, Plate 7, figs. 1a, 2a–b, 3a.

Dentaliida sp. M: Brandt (2022): 157, 158, 166, Tab. 5.26, fig. 5.96; Sigwart et al. (2025): fig. 4L.

“deep-sea scaphopod-anemone association”: Linse and Neuhaus (2024): 14.

Laevidentalium wiesei: Sigwart et al. (2025): tab. 1.

Shell up to 45.6 mm long, maximum ventral aperture length 6.7 mm, ventral aperture width to 7.4 mm (holotype, Fig. 15A–D: 38.5 mm long, ventral aperture length 5.4 mm, ventral aperture width 5.9 mm), thin, but solid, tusk-shaped, gently recurved, with point of maximum curvature close to the mid-point of shell length in most of the specimens, located either dorsally or ventrally of it (Table 4). Outer surface glossy, ivory white to corneous in colour, ornamented with fine, densely arranged, irregular prosocline growth lines, without longitudinal (dorso-ventral) sculpture (Fig. 15I, K, Fig. 16L); growth interruptions are apparent at irregular intervals, but rather inconspicuous (Fig. 16G) and partly obscured by corrosion; intermediate shell layer white where exposed. Aperture subcircular, slightly wider than long (Table 4, Fig. 16H – bottom virtual section), edge prosocline, sharp. Dorsal (apical) end of the shell eroded in all specimens known, with the exposed intermediate and/or inner shell layers taking various shapes, either truncate (e.g. HNC 43946 – Sahlmann (2012)), shallow ring-like (e.g. HNC 82015, Fig. 15I–J) or more or less irregularly notched due to breakage along different sides (e.g. HNC 43947 – Fig. 15C, SMF 366426 – Fig. 16E–F); apical lumen circular in cross-section (Fig. 16H – middle virtual section). Protoconch morphology unknown. Inner shell surface white, smooth and glossy. Anterior (concave) side of shell often hosts an unidentified (and potentially undescribed) species of large-sized (up to 23 mm in preserved specimens) epibiotic sea anemone (Table 4, Fig. 15A–B, Fig. 15D, Fig. 16A, Fig. 16H–K); CT scans revealed no evidence of the anemone corroding or penetrating the scaphopod shell (Fig. 17A).

Figure 15.  

Laevidentalium wiesei Sahlmann, 2012, type material. A–D Holotype HNC 43947, anterior (A), right side (B), posterior (C) and left side (D) views. Note the dry remains of the epizoic anemone attached to the anterior face of the shell; E–K Paratype HNC 82015, anterior (E), right side (F), posterior (G) and left side (H) views; dorsal aperture in lateral (I; scanning electron micrograph) and apical (J) view; scanning electron micrograph showing the microsculpture consisting exclusively of densely arranged incremental lines (K). Scale bars: 10 mm (A–H), 1 mm (I, K), 0.5 mm (J).

Figure 16.  

Laevidentalium wiesei Sahlmann, 2012, specimens from the AleutBio expedition. A–H Specimen SMF 366426, anterior (A), right side (B), posterior (C) and left side (D) views; close-ups of dorsal part of shell in posterior (E) and right side (F) view; detail of postero-ventral shell portion with growth mark indicated by arrowhead (G); micro-CT-based 3D reconstruction (left side view) and virtual cuts through the shell (perpendicular to the central axis) (H). Note the subcircular – wider than long – lumen of the ventral part of the shell that becomes circular dorsally; I–K Specimen SMF 373200 (shell broken during sampling event), right side (I) and posterior (J) views; close-up of the epizoic anemone attached to the anterior face of the shell (K); L Shell fragment from lot SMF 366427, scanning electron micrograph showing microsculpture. Scale bars: 10 mm (A–D, H – shell reconstruction, I–J), 5 mm (E–F, K), 2.5 mm (G), 2 mm (H – virtual shell sections), 1 mm (L).

Figure 17.  

Laevidentalium wiesei Sahlmann, 2012, anatomy and radula. A Specimen SMF 366426, virtual cross section from x-ray tomography with major internal structures indicated. Abbreviations: DV muscle, dorso-ventral muscle; B–G Specimen SMF 373200, virtual cross sections from x-ray tomography showing tests of ingested foraminifera (B–C; scaphopod soft body not shown for clarity), overview of radula (D; Abbreviations: cen, central tooth; lat, lateral tooth; mar, marginal tooth), close-up of lateral and marginal teeth (E), of central tooth (F) and detail of granulose face of the latter (G). Scale bars: 10 mm (A), 1 mm (B–C), 0.5 mm (D–E), 0.1 mm (F), 0.03 mm (G).

Gross anatomy (Fig. 17) follows typical dentaliid body plan (Fig. 17A); preserved body length of SMF 366426 (23.5 mm) around half the shell length (45.6 mm), gonad visible in CT scan is likely male. Captacular mass large and very dense. Dorsal pavilion relatively long (3 mm), robust.

Radula well-developed, with five teeth per row (formula 1-1-1-1-1; Fig. 17D); mature teeth brown in colour/mineralised, consistent with a foraminifera-dominated diet (Fig. 17B–C). Central teeth crescent-shaped, with convex superior face (eroding to concave in worn teeth) and adjacent granulose face (Fig. 17F–G); lateral teeth dumb-bell-shaped without cusps on working surface (Fig. 17D–E), marginals rather stout for the genus (cf. Glover et al. (2003) Lamprell and Healy (1998), Glover et al. (2003)), upright rectangular with rounded corners, basal part almost straight-sided, bent on quarter closest to lateral teeth (Fig. 17E).

Adult shell length to > 45 mm, ratio of shell length to ventral aperture length 7–9, gently recurved, without longitudinal keels, surface glossy, but often heavily corroded, smooth, except for dense prosocoline incremental lines; colour ivory white to corneous; ventral aperture subcircular, slightly wider than long, prosocline and sharp-edged. Anterior shell face usually hosting a single epibiotic sea anemone. Radula with crescent-shaped central teeth with granulose anterior face, lateral teeth without cusps, marginals rather stout for the genus, rectangular with rounded corners, basal part almost straight-sided, bent on quarter closest to lateral teeth.

Known from the abyssal plain east of the Kuril Kamchatka Trench (type locality; Sahlmann (2012)) and the southern edge of the eastern Aleutian Trench (Sigwart et al. 2025, this study) at depths of 4500–5210 m. Sahlmann (2012) suspected that the records of “Laevidentalium sp.” reported by Okutani (1975), p. 76, from R/V SOYO-MARU Station 150 (Philippine Sea southeast of Kyushu, Japan, 29°52.4’N, 133°06.2’E, 3610 m water depth) and R/V KAIYO-MARU Station D (abyssal plain east of northern Honshu, Japan, 36°03.2’N, 157°51.4’E, 4370 m water depth) might correspond to this species; alternatively, these records may concern a closely-related species or species complex (see remarks in Okutani (1975)).

Two other Laevidentalium species have been recorded from abyssal depths in the Pacific Ocean – L. largicrescens (Tate, 1899) and L. leptosceles (R. B. Watson, 1879). Both can be distinguished from L. wiesei by shell and radula characters; furthermore, no Laevidentalium species other than L. wiesei is known to host an epibiotic sea anemone. Laevidentalium largicrescens is conchologically most similar, but differs from L. wiesei by the circular ventral aperture, the occasional presence of a posterior apical notch, cusps on the working surface of the lateral radular teeth and sigmoidal, much more elongated marginal teeth. It has a very different geographical range, occurring in the Southern Hemisphere, off the eastern Australian coast at 284–3058 m depth (Lamprell and Healy 1998). Laevidentalium leptosceles (R. B. Watson, 1879) is more slender, bears a weak, flexuous longitudinal sculpture in the apical part of the shell – lacking in the synonymised, shallower-water taxon L. banale (Boissevain, 1906) – and has a subcircular apical cross-section (Watson 1879, Lamprell and Healy 1998); it is widely distributed in the Indian Ocean and Western Pacific, with live records ranging from 2200–5300 m depth (Scarabino 1995).

The Atlantic abyssal L. abyplainae Scarabino & Scarabino, 2011, differs – besides its biogeography – by a straighter shell that expands less in diameter towards the ventral aperture, as well as by the presence of fine longitudinal striations on its apical part (Scarabino and Scarabino 2011, Sahlmann 2012). It shares with L. wiesei the granulose anterior face of the central radular teeth, but the lateral teeth are shaped differently and bear cusps (Scarabino and Scarabino 2011); the marginal teeth are relatively shorter than in L. wiesei.

The only large-sized scaphopod within the North Pacific recorded at abyssal depths and superficially resembling L. wiesei is Rhabdus toyamaensis (Kuroda & Kikuchi, 1933). Although it usually inhabits much shallower depths (Kuroda and Kikuchi 1933, Habe 1964, Habe 1977, Okutani 2000), a single specimen was collected at 5100 m in the Aleutian Trench, south of Attu Island (52°12’N, 175°44’E) (Sahlmann (2015), as Rhadbus toyamaense (Kuroda & Kikuchi, 1933)). Rhabdus toyamaensis attains much larger sizes than L. wiesei (up to 10 cm long), is more slender (the ventral aperture diameter of the Aleutian Trench specimen is just 4 mm at 61.5 mm shell length), has a completely circular ventral aperture and a shell sometimes bearing alternating light and dark bands. The abyssal specimen reported by Sahlmann (2015) – besides its unusual bathymetric and geographic location – also shows morphological differences from typical R. toyamaensis, such as subtle, but clearly visible annular swellings along the shell in addition to regular growth increments and an extremely glossy surface, suggesting it might actually be an undescribed species.

The most obvious feature of L. wiesei is the epizoic anemones attached to the anterior shell face of live individuals, an association previously reported only from members of the genus Fissidentalium (Dall 1908, Shimek and Moreno 1996, Shimek 1997, Linse and Neuhaus 2024). The shells of these species – F. actiniophorum Shimek, 1997, F. aurae Linse & Neuhaus, 2024, F. megathyris (Dall, 1890) and F. peruvianum (Dall, 1908) – however, all have distinct longitudinal ribs, which differentiate them at first sight from the smooth-shelled L. wiesei.

Laevidentalium wiesei Sahlmann, 2012 was originally described, based on four empty shells collected at abyssal depths in the Kuril Kamchatka Trench region, north-west Pacific Ocean. The type material, entirely housed in the malacological collection of Haus der Natur – Cismar (Germany), was obtained by the Museum in 1995 from private shell collections, accompanied by only basic locality data. Following its description (Sahlmann 2012), no further records of this poorly-known species were published until several, mostly live-collected, specimens were sampled in 2022 by the AleutBio expedition to the Aleutian Trench and adjacent abyssal parts of the Bering Sea, north-east Pacific Ocean (Brandt 2022, Sigwart et al. 2025). This new material enabled a more detailed, integrative re-description and constitutes a significant geographic range extension.

Specimens of L. wiesei from the SO293 AleutBio expedition were collected using a 3.5 m-wide Agassiz trawl with 10 mm cod end mesh size (OKTOPUS GmbH). Contents of the net were sieved on a 1 mm mesh and subsequently preserved in 96% ethanol (lots SMF 366425, SMF 366426, SMF 366427 and SMF 373200) or 4% buffered formalin-seawater (SMF 374281; Brandt (2022)).

Photographs of entire scaphopods were taken with a CANON EOS 6D camera, equipped with an EF 100 mm 1:2.8 IS USM macro lens and serial images stacked with Helicon Focus software (v. 5.3 X64; HELICON SOFT). Details of the outer shell surface were photographed using: (i) a motorised NIKON SMZ25 stereomicroscope with an attached NIKON Digital Sight 10 camera and (ii) a HITACHI TM4000Plus Tabletop scanning electron microscope (SEM) without metal coating. Stereo-microscopic images were stacked with NIKON NIS Elements Basic Research (BR) software (v. 5.42.04).

After initial photographic documentation, shell shape and soft body anatomy were studied by micro-computed tomography (micro-CT), using a WERTH TomoScope XS Plus CT scanner with the following settings [scan of SMF 373200/scan of SMF 366426]: acceleration voltage 60/80 kV, emission current 180/200 µA, exposure time 666 ms, voxel size 6.29/21.81 µm, number of images per revolution 2000/1000. Prior to CT scanning, specimens had been contrasted in a solution of 0.3% phosphotungstic acid and 3% dimethyl sulphoxide in 95% ethanol (Senckenberg Ocean Species Alliance (SOSA) et al. 2024) for 27 days. X-ray virtual sections were produced in Dragonfly software (v. 2022.2; OBJECT RESEARCH SYSTEMS). The 3D shell reconstruction of SMF 366426 and virtual shell sections were obtained by first cropping the raw tomographic dataset in Avizo3D (v. 2024.1; THERMO FISHER SCIENTIFIC) and postprocessing the resultant file in VGSTUDIO MAX (v. 2024.3; VOLUME GRAPHICS). The tomographic datasets and the surface model of SMF 366426 are available from Zenodo (https://doi.org/10.5281/zenodo.15470822).

Shell morphometric measurements follow Shimek and Moreno (1996) and were taken from macrophotographic images using NIS Elements BR software.

For radula preparation, the entire buccal mass of specimen SMF 373200 was dissected and the soft tissue dissolved in diluted commercial bleach (a 5% sodium hypochlorite solution). Following a ca. 10 s cleaning step in an ultrasonic bath (cf. Shimek and Moreno (1996)), the radula was dehydrated in absolute ethanol, transferred to hexamethyldisilazane (HMDS) through an ascending series of ethanol-HMDS mixtures and finally left to air-dry at room temperature in a fume hood overnight. The preparation was subsequently mounted on an aluminium stub with a double-sided adhesive tab, sputter-coated with gold-palladium and imaged using a HITACHI TM4000Plus Tabletop SEM.

Figure plates for this contribution were assembled with Adobe Photoshop 2025.

COI sequences of L. wiesei were obtained by the procedures detailed in Linse and Neuhaus (2024).

Specimen data for this description were gathered and processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Repository: Type material is held at Haus der Natur – Cismar (HNC), Cismar, Germany and additional specimens at the Senckenberg Research Institute and Natural History Museum Frankfurt (SMF).

Holotype

Dimensions: Length: 7.4 mm; Height: 4.1 mm; Width: 3.1 mm (Fig. 18A–C).

Figure 18.  

Myonera aleutiana Machado & Sigwart, sp. nov. shell and anatomy. A–C Photomicrography of holotype (SMF 373402), right and left valves plus a dorsal view, respectively; D–R Paratype (SMF 374320), right and left views, respectively; F–R Selected X-ray slices/images showing the arrangement and details of the pallial cavity organs and visceral mass; F–G Tomographic sagittal sections of different parts of the specimen; purple, yellow, red and green squares indicate the approximate areas of the transversal sections; H–R Tomographic transversal sections, from posterior to anterior orientation. Abbreviations: ap, anterior labial palp; aam, anterior adductor muscle; arm, anterior pedal retractor muscle; asm, anterior septal retractor muscle; b, bubble (artifact); bs, broken shell area; bt, byssal thread; ceg, cerebro-pleural (= circum-esophagic glanglia); css, crystalline style sac; dd, digestive diverticula; es, exhalant siphon; est, exhalant siphonal tentacles; f, foot; fl, foliaceus lamellae; gc, gastric caecum; gs, gastric shield; h + k, heart + kidney; hg, hind gut; hs?, haemocoel spaces; il, Inhalant lateral sinus; is, inhalant siphon; isc, infra-septal chamber; iss, inter-siphonal septum; ist, inhalant siphonal tentacles; lit, lithodesma; m, mouth; mm, mantle margin (ventral); o, oesophagus; ov, ovary; p, prey(s) inside stomach; pp, posterior labial palps; pu, pustules; pII, prodissoconch II; pam, posterior adductor muscle; prm, posterior pedal retractor muscle; r, rostrum; rr, radial ridge; rv, right valve; s, septum; sp, septal pores; sm, septal membrane; sr, secondary ridge; st, stomach; sph, sphincter of inhalant siphon; ssc, supra-septal chamber; ssh, siphonal sheath; u, umbones. Scale bars: 1.5 mm (A–C), 1 mm (D–R).

Paratype

Dimensions: Length: 6.8 mm; Height: 3.5 mm; Width: 2.5 mm (Fig. 18D–R). This individual presents a single and short byssal thread (bt), visible both through the shell's transparency and in tomographic images.

Shell small (up to 7.4 mm in length), extremely fragile, translucent to olive, inflated, inequilateral, elongate, rostrate, slightly inequivalve; posterior dorsal margin almost straight, anterior dorsal margin wider and rounded, dorsal and posteroventral margins of right valve (rv) overlapping left (lv) (Fig. 18A–E); umbones inflated and rounded, slightly prosogyrate; prodissoconch I barely visible, prodissoconch II (pII) (1040 ± 20 μm, n = 2) elliptical, smooth, well preserved in the two individuals analysed (Fig. 18C). External surface with 16-18 equidistant concentric foliaceous lamellae (fl), covering the entire shell, extending to the umbo (u) and complete to the rostral ridge (Fig. 18A–E); countless small pustules (pu) present between the lamellae. Prominent rostral ridge (rr) present, with a secondary ridge (sr) parallel to the posterior dorsal margin, usually visible (Fig. 18D). Hinge edentulous. Resilifer and lithodesma (lit) elongate, deflected, posteriorly pointed.

Anatomy:

Mantle margin with two fused points, anteriorly forming short pedal gape and posteriorly forming siphonal apertures; posteroventrally, mantle margin (mm) fusion (Fig. 18J-Q) probably involving inner and middle folds (Type B) (Yonge 1982); absence of fourth pallial aperture. No evidence of arenophilic glands (= radial mantle glands), likely due to the resolution limitations of the micro-CT scan, as these glands are commonly found in cuspidariids (Morton and Machado 2019).

Siphons separated, inter-siphonal septum (iss) present; inhalant (is) large and contracted (Fig. 18H), probably funnel-shaped; both surrounded by small finger-shaped tentacles at base, four in inhalant and three in exhalant siphon (es), encased in a thin and muscular siphonal sheath (ssh) (Fig. 18G-I). Inhalant lateral sinus present (il). Inhalant sphincter (sph) in the base of the inhalant siphon, which is dorsally attached to the posterior septal retractor muscle (prm) (Fig. 18F, K). The inhalant sphincter plays a crucial role in regulating water flow and the intake of prey into the infra-septal chamber (isc) and appears to be present exclusively in members of Cuspidariidae (Machado et al. 2016). Carnivorous bivalves with highly modified inhalant siphons, often regarded as active predators (e.g. Allogramma formosa (Jeffreys, 1882) or Poromya granulata (Nyst & Westendorp, 1839)), do not possess an inhalant sphincter.

Septum horizontal, pierced by four pores (sp) is present dividing the mantle cavity into infra (ventral/isc) and supraseptal (dorsal/ssc) chambers (Fig. 18F, G, L-O). It is suspended in the mantle cavity by posterior and bifurcated anterior septal retractor muscles (psm/asm), attached to the shell valves just above their respective adductor muscles and lie close to the pedal retractor muscles (prm/arm). Lateral septal retractor muscles (lsm) present being more concentrated posteriorly. Extra lateral septal muscle, absent. Left and right halves of the septum are united by the septal membrane (sm), which separates anteriorly to create the siphonal gape through which the foot can protrude (Fig. 18O).

Labial palps small and reduced, anterior and posterior palps present (Fig. 18F). Posterior palps (plp) flattened and located along the postero-lateral margins of the funnel-shaped mouth (m). Anterior palps (alp) greatly reduced and unattached to the posterior ventral surface of the anterior adductor muscle (aam). Unlike most Cuspidariidae, M. aleutiana sp. nov. does not have the anterior palp attached to the anterior adductor muscle, likely due to the effects of fixation (Yonge 1928, Machado et al. 2016).

Posterior and anterior adductor muscles present (pam/aam), isomyarian; with posterior and anterior pedal retractor muscle (prm/arm); posterior pedal and anterior septal retractor muscles (prm/asm) bifurcated and dorsally attach to the shell close to the posterior adductor muscle (Fig. 18G, Q).

Foot with small, unpronounced heel (Fig. 18F, L–O); presence of a single byssal thread (bt) (Fig. 18O). The presence of byssus threads in Anomalodesmata is rare, having been documented in only 14 species to date (Yonge 1952, Allen and Turner 1974, Morgan and Allen 1976, Krylova 1993, Leal 2008, Simone and Cunha 2008, Machado et al. 2016, Senckenberg Ocean Species Alliance (SOSA) et al. 2024), including M. aleutiana sp. nov. Amongst the Cuspidariidae, so far, only Cardiomya cleryana (A. d'Orbigny, 1846) has had its long and single byssus thread documented through illustrations and video recordings (Machado et al. 2016). The new species is, therefore, the first known representative of Myonera to exhibit this feature. The potential functions of the byssus thread in deep-sea carnivorous bivalves have never been tested, but it likely aids in anchoring within the sediment, as lie-in-wait predators require stability to effectively capture their prey. A small pebble can be observed attached to the distal portion of the byssus thread in the new species, reinforcing the anchorage hypothesis (Fig. 18O).

Digestive system with funnel-shaped mouth (m), opening into a short and muscular oesophagus (e) that enters into the anterodorsal portion of the stomach (s) (Fig. 18F, P, Q); stomach Type II (Purchon 1987, Purchon 1990) with a muscular wall (sw), well developed, rounded, with gastric shield (gs), prey inside (p) and associated with a crystalline style sac (css) not conjoined with the mid-gut; surrounded dorsally, anteriorly and laterally by female gonads (ov) and the digestive gland; digestive diverticula (dd) with large gastric caecum (gc) (Fig. 18F, G, N-P).

Pericardium/heart + kidney (h+k) area reduced and poorly visible (Fig. 18G, L). Haemocoel spaces (hs?) probably present in the anterior portion of the visceral mass (Fig. 18F, N).

Probably dioecious, ovary (ov) well visible (> 40 mature oocytes counted, ~ 100 μm in diameter); only mature oocytes observed i.e. larger and usually free in the ovarian lumen (Fig. 18F, M). Testis not found/visible. Although the measurements of prodissoconch I are unavailable, other evidence — such as the small body dimensions (miniaturisation) and the possibility that mature oocytes are encapsulated oocytes (post-fertilisation) — could support the hypothesis of brooding care in Myonera aleutiana sp. nov. The brooding care has already been described for other anomalodesmatans, such as members of the Spheniopsidae (Morton et al. 2016a, Morton et al. 2016b) and hypothesised for the verticordioideans Trigonulina ornata d'Orbigny, 1853 and Lyonsiella illaesa Machado & Sigwart, 2024 (Morton et al. 2019, Senckenberg Ocean Species Alliance (SOSA) et al. 2024).

Cerebro-pleural ganglia (ceg) present and visceral ganglia not visible. Pedal ganglia (pg) present, with no statocysts associated.

Shell translucent to olive, thin, fragile, inflated, rostrate; posterior dorsal margin almost straight; presence of two rostral ridges; dorsal and posteroventral margins of right valve overlapping left; outer surface with 16-18 equidistant concentric foliaceous lamellae covering the entire shell with countless small pustules present between them; anterior septal retractor muscle bifurcated; extra lateral septal muscles absent; reduced kidney and pericardial cavity; presence of a single and short byssus thread; probably dioecious.

The specific epithet aleutiana refers to the species type locality, the Aleutian Islands.

Known only from the Aleutian Islands, off Alaska, North Pacific. Bathymetric range: 5170–5280 m, a new record for the genus previously recorded at 4400 m depth in the Tasman Sea, Southwest Pacific (see Knudsen (1970)).

The genus Myonera presents significant challenges in distinguishing between some of its species, as well as from certain species of Cuspidaria Nardo, 1840 and Rengea Kuroda & Habe, 1971, due to the overlap of anatomical and shell features. The new species was, therefore, compared with all morphologically similar species from these three genera through a detailed examination of the holotypes and/or original illustrations (Fig. 19). In general, Myonera and Rengea are distinguished by the presence of radial and concentric elements forming the outer sculpture in the former and only the presence of strong concentric plications in the latter. Additionally, Rengea have umbones depressed and more elongated shells. In Cuspidaria, the presence of a posterior lateral tooth in the right valve is the key feature that differentiates it from the other two genera – both edentulous.