Placiphorella sp. nov.: Sellanes et al. 2004: 1066.

Placiphorella atlantica: Sellanes et al. 2008: 1105, non Placiphorella atlantica (A. E. Verrill & S. I. Smith in Verrill, 1882).

Placiphorella sp.: Schwabe and Sellanes 2010: 47, Figs. 14 I–J, 15.

Placiphorella sp.: Schwabe 2010: 172, Fig. 1B, 174: Fig. 3B, 188: Fig. 18A.

Body of medium size (18–30 mm x 12–23 mm, holotype 30 mm x 23 mm), broadly oval, low-elevated, subcarinated, side slopes straight to slightly convex; valves not beaked or with small, not pronounced apex (Fig. 1). Tegmentum minutely and irregularly granulated, white or yellowish, usually mottled with brown along the posterior valve margins; girdle broadly expanded anteriorly, usually white mottled with light-brown and brown (Figs 1, 2). See Schwabe and Sellanes (2010), Figs. 14 I–J and 15, for additional holotype photograph and detailed SEM photos of the girdle spicules and radula.

Figure 1.  

Placiphorella methanophila Vončina, sp. nov., dorsal view. A Holotype, ZSM Mol 20041044, body length: 29 mm; B Paratype, SMF 376539, body length: 26 mm. Scale bar: 5 mm.

Figure 2.  

Placiphorella methanophila Vončina, sp. nov. A, D Paratype. ZSM Mol 20080824; B, C, E–G Holotype, ZSM Mol 20041044. A–C. Valves I, VII, VIII, respectively, dorsal view; D–F Valves I, VII, VIII, respectively, ventral view; G Valve VIII, lateral view. Scale bar: 2 mm.

Head valve crescent-shaped, front slope straight, posterior margin very widely V-shaped, with a small median notch and little raised apex, tegmentum minutely and irregularly granulated, with some inconspicuous, irregular radial ridges and concentric growth lines (Figs 1, 2A and D). Intermediate valves broadly rectangular, very wide, with valve III being the widest, short, front margin widely angular, weakly projected forward at jugal part; side margins rounded, hind margin concave, apex weakly or not indicated, lateral areas raised, bordered by raised diagonal ribs, interspace shallowly excavated, crossed by conspicuous concentric growth lines (Figs 1, 2B and E). Tail valve small, roughly triangular in outline, about half as wide as widest intermediate valve, front margin straight to slightly convex, hind margin with a shallow or obsolete caudal sinus, mucro distinct, raised, terminal, overhanging, antemucronal area almost straight, postmucronal area slightly convex, tegmentum with two ribs separating the ante- and postmucronal areas (Fig. 2C and F–G).

Articulamentum strongly developed, white, valves calloused, apophyses very wide, short, slightly rounded to subtrapezoidal, trapezoid in the tail valve, separated by a narrow jugal sinus, insertion plates short, slit formula 15–16/1/sinus, slits shallow, no slit rays, teeth thick, bilobed and crenulated (Fig. 2).

Girdle broadly expanded anteriorly, uniformly brown or yellowish, dorsally covered with two kinds of spicules: single, smooth, and sharply pointed spicules, L: 75–100 μm (mean = 85 μm, n = 5), W: 15–25 μm (mean = 21, n = 5) and similar, but longer spicules gathered in groups of a few, L: 107–250 μm (mean = 120 μm, n = 12), W: 12–17 μm (mean = 15 μm, n = 5) (Fig. 3A–C). Sparsely scattered (more numerous near the front) large bristles, beset with slender, smooth and sharply-pointed spicules, L: 268 μm (n = 1), W: 29–36 μm (mean = 32 μm, n = 4), arranged in oblique series along axis (Fig. 3D). Marginal fringe composed of straight, smooth, sharp-topped spicules, L: 120–135 μm (mean = 125 μm, n = 3), W: 15–20 μm (mean = 17 μm, n = 5) (Fig. 3D). Ventral girdle spicules smooth, flattened, L: 80 μm (n = 1), W: 18–20 μm (mean = 19 μm, n = 2). Pallial fold with 6–14 tentacles, up to 2 mm in length with the middle ones the longest, spicules of the precephalic tentacles smooth, sharply-pointed L: 120–150 μm (mean = 130 μm, n = 5), W: 15–20 μm (mean = 17 μm, n = 5) (Fig. 3E).

Figure 3.  

Placiphorella methanophila Vončina, sp. nov. A–B. Specimen from ZIN collection (ZIN 2587), photos by courtesy of Boris Sirenko. C–F. Holotype, ZSM Mol 20041044. A–B. Dorsal spicules of perinotum; C. Longer dorsal spicules of perinotum clustered in groups; D. Bristle with spicules and marginal spicules; E. Spicules of precephalic tentacles; F. Central portion of radula. Scale bars: 200 µm (A –D) , 50 µm (E) , 20 µm (F).

Radula of holotype small, 5.8 mm in length, with 52 rows of teeth, of which 42 are of mature. Central tooth subrectangular, with wide base and curved blade, first lateral tooth elongate, wing-shaped with a narrow blade, major lateral tooth with tricuspid head, denticles pointed, central denticle somewhat longer than others, outer denticle widest and shallowest notched, first uncinal very prominent with high elevated lamellae, major uncinal elevated, slender with only slightly increased tip (Fig. 3F).

Gills merobranchial, 13–18 ctenidia per side (15 and 18 on the left and right side, respectively, in the holotype) in specimens 18–30 mm long.

Chitons of medium size, up to 30 mm, body broadly oval, girdle expanded anteriorly; colour of the tegmentum white or yellow, mottled with brown; girdle white with light-brown and brown maculation. Valves depressed, subcarinated, minutely and irregularly granulated. Tail valve roughly triangular in shape, mucro terminal, overhanging. Girdle covered with two kinds of spicules: single, smooth and sharply pointed spicules and similar, but longer spicules gathered in groups of a few; sparsely scattered large bristles beset with elongated slender spicules.

Molecular diagnosis: COI: 132 – C , 168 – G, 258 – A, 267 – C, 300 – T, 348 – C, 411 – A, 420 – A, 438 – G.

The specific epithet methanophila is a feminine adjective formed from the Latin noun methanum = methane, and the suffix -phila = “loving”, “friendly” or “friend”, underlining the close association of the new species with methane seeps.

At present, only known from off Concepción, Chile; all specimens found in close relationship to the methane seeps (see discussion of Chilean records of P. pacifica in Schwabe and Sellanes (2010): 48).

Phenotypic characters discussion:

There are five species that share a head valve incision number > 10 with Placiphorella methanophila sp. nov., namely Placiphorella atlantica (Verrill & S.I. Smith, 1882), P. laurae Clark, 2019, P. isaotakii Saito, Fujikura & Tsuchida, 2008, P. okutanii Saito, Fujikura & Tsuchida, 2008 and P. pacifica S. S. Berry, 1919. However, they differ from the new species by several characters, named below:

1. Placiphorella methanophila sp. nov. differs from P. atlantica (source: Kaas and Van Belle (1994); Clark (1994)) by the shape of the tail valve (see also Schwabe and Sellanes (2010), Figs. 14 J–L for comparison; triangular with the straight antemucronal area in P. methanophila sp. nov. vs. trapezoidal with the concave antemucronal area in P. atlantica); sculpture of dorsal spicules (smooth, single and sharply pointed in P. methanophila sp. nov. vs. longitudinally striated and mamillated in P. atlantica); by the sculpture and size of marginal spicules (smooth and 120–135 μm long in P. methanophila sp. nov. vs. striated and 80 μm long in P. atlantica);
2. Placiphorella methanophila sp. nov. differs from P. isaotakii (source: Saito et al. (2008)) by the sculpture of the tegmentum (minutely and irregularly granulated in P. methanophila sp. nov. vs. densely packed, elongate granules, occasionally merging into longitudinal threads in P. isaotakii); by the girdle ornamentation (smooth, single and sharply pointed, 75–100 μm long and similar, but gathered in groups and longer, 107–250 μm in P. methanophila sp. nov. vs. spicules mamillated at tip 50 μm × 40 µm long and longer, grouped spicules, 440 µm long in P. isaotakii); number of gills (13–18 gills in P. methanophila sp. nov. vs. 20–21 gills in P. isaotakii);
3. Placiphorella methanophila sp. nov. differs from P. laurae (source: Clark (2019)) by the shape of the tail valve (straight antemucronal area, obtuse triangle-shaped in P. methanophila sp. nov. vs. concave antemucronal area, acute-angle triangle in P. laurae); length of dorsal spicules (107–250 μm long in P. methanophila sp. nov. vs. 400 μm long in P. laurae); size of spicules of bristles: 268 x 29–36 μm in P. methanophila sp. nov. vs. 350 x 40 μm in P. laurae;
4. Placiphorella methanophila sp. nov. differs from P. okutanii (source: Saito et al. (2008)) by the shape of the tail valve (widely triangular in outline in P. methanophila sp. nov. vs. inversed trapezoidal, less wide in P. okutanii); by the dorsal girdle ornamentation (single sharply pointed spicules, 80–100 x 24–25 μm and similar, but clustered together spicules 107–250 μm x 12–17 μm in P. methanophila sp. nov. vs. spicules mamillated at tip 150 μm × 30 µm and longer, grouped spicules, 400 x 50 µm in P. okutanii);
5. Placiphorella methanophila sp. nov. differs from P. pacifica (source: Berry (1919)) by the sculpture of the tegmentum (minutely and irregularly granulated in P. methanophila sp. nov. vs. smooth in P. pacifica); by the sculpture of the head valve (inconspicuous, irregular radial ridges in P. methanophila sp. nov. vs. 12-14 low, radiating ribs in P. pacifica); position of the mucro (terminal in P. methanophila sp. nov. vs. subterminal in P. pacifica).

Genetic discussion:

The ranges of uncorrected genetic p-distances between Placiphorella methanophila sp. nov. and all Placiphorella available from GenBank in mitochondrial cytochrome oxidase subunit 1 (COI) gene sequences ranged from 4.1% to 14.6% (Table 1). The closest COI sequences are: KJ574090 (4.1% distance), representing Placiphorella sp. A from Irisarri et al. (2014), which was mentioned by authors as a potentially new species, but the description has never been published; and GU806074, GU806077-8, GU806080, GU806115 and GU806118 (4.6–5.0% distance) representing P. atlantica, from which P. methanophila sp. nov. can be also differentiated morphologically.

Lepetodrilus aff. schrolli MT: Johnson et al. (2008): fig. 1, table 2; Giguère and Tunnicliffe (2021): table 2

Lepetodrilus aff. schrolli Mariana Trough: Poitrimol et al. (2022): fig. 2A

Shell (Fig. 4): very loosely coiled, juvenile shell becomes limpet-shaped in adult stages. Medium-sized for genus, aperture oval, maximum shell length around 8.5 mm. Shell dimensions of the holotype and paratypes 1–5 are given in Table 2. Apex at posterior end of shell (Fig. 4A) or protruding beyond it (Fig. 4C) depending on substrate morphology, also influencing shell height. Fine concentric ribs (Fig. 5C) present across all growth stages, adults developing broad, strongly raised concentric ridges to give strongly undulated profiles (Fig. 4A-F, see lateral views); strength and frequency of latter ridges varying amongst individuals. Shell microstructure (Fig. 5D) with thin outer homogenous layer and thick inner complex crossed lamellar layer, numerous fine shell pores are presented perpendicular to shell surface. Protoconch (Fig. 5B) indistinctly coiled, approximately 170 μm in diameter. Protoconch sculpture corroded and indiscernible on all specimens investigated. Periostracum light green, smooth, moderately thick, enveloping edge of shell.

Figure 4.  

Lepetodrilus marianae Chen, Watanabe & Tsuda, sp. nov., habitus photographs of representative type specimens. A Holotype (SMF 373150), dorsal, ventral and lateral views; B Paratype 1 (NSMT-Mo 79482), dorsal, ventral and lateral views, arrowhead on ventral view indicates the penis; C Paratype 2 (NSMT-Mo 79483), dorsal, ventral and lateral views; D Paratype 3 (MNHN-IM-2019-34806), lateral view; E Paratype 4 (MNHN-IM-2023-431), dorsal and lateral views; F Paratype 5 (SMF 373151), dorsal and lateral views. Scale bars: 2 mm.

Figure 5.  

Lepetodrilus marianae Chen, Watanabe & Tsuda, sp. nov., scanning electron micrographs, NSMT-Mo 79485. A Radula (r, central or rachidian tooth; 1–5 denoting lateral tooth from inside to outside; m, marginal teeth); B Protoconch; C Fine concentric sculpture on shell surface; D Fractured cross section of a shell showing microstructure (arrowheads indicate shell pores). Scale bars: 100 μm (A, B, D), 50 μm (C).

External anatomy (Fig. 4A–C) overall typical for Lepetodrilus. Oval foot, muscle scar horseshoe-shaped, left arm longer than right arm. Cephalic tentacles simple, conical, extending from broad base. Eyes lacking. Penis in males simple conical with narrow base, tapering to blunt tip, seminal groove on dorsal side. Two pairs of epipodial tentacles present on posterior end of foot, simple conical with broad base. Mantle edge with two folds, outer fold thin, extending to edge of periostracum; inner fold thick, densely lining with (presumably sensory) small tentacles. Operculum lacking.

Radula (Fig. 5A) rhipidoglossate, formula ca. 25-5-1-5- ca. 25. Central (rachidian) tooth low with broad shaft carrying one lateral ridge on either side, rapidly tapering to single narrow, pointed cusp with smooth cutting edges. Innermost lateral (‘1’, Fig. 5A) twice as broad as central tooth, with slanted, very broad overhanging cusp only carrying very weak serrations on outermost one-third. Three middle laterals (‘2–4’, Fig. 5A) narrower, of similar breadth to central tooth, carrying simple triangular overhanging cusps, inner edges carrying weak serrations, outer edges smooth. Outermost lateral (‘5’, Fig. 5A) much broader again, with triangular overhanging cusp carrying weak serrations on inner edge plus strong serrations on outer edge. Marginals with very elongated shafts ending in spoon-like cusps finely serrated into about 20 denticles, innermost denticle strongest by far. Size of marginals decrease gradually outwards.

A medium-sized Lepetodrilus with two types of concentric sculpture: regular, fine concentric ribs across all growth stages and irregular, strongly raised concentric ridges in adults. Apex at the posterior end of shell or overhanging it.

The specific epithet marianae is a noun in the genitive case, after the species distribution range in Mariana Arc and Mariana Trough. This species was amongst many western Pacific vent gastropods first recognised as new by the late German malacologist Lothar A. Beck (Chen and Sigwart 2023). During the course of searching for unpublished material and manuscript by Beck (see Chen and Sigwart (2023)), we came across unpublished writing by Beck and his former student Kathrin Sobjinski suggesting the specific epithet marianae for this species, which we have decided to honour.

Specimens of L. marianae Chen, Watanabe & Tsuda, sp. nov. have been collected at several hot vent fields in both Mariana Arc (northwest Eifuku, northwest Rota, Seamount X) and Mariana Trough (Alice Springs, Illium, Burke, Hafa Adai, Perseverence, Forecast, Snail and Archaean), confirmed by COI sequences (Johnson et al. 2008, Giguère and Tunnicliffe 2021).

Lepetodrilus is a genus of vetigastropod limpets commonly found in hydrothermal vents globally. The first comprehensive molecular phylogenetic reconstruction of this genus using the COI gene by Johnson et al. (2008) revealed that Lepetodrilus inhabiting the south-western Pacific vents consisted of three cryptic species showing clear barcoding gaps, including L. schrolli L. Beck, 1993 from Manus Basin, ‘Lepetodrilus aff. schrolli LF’ from Lau and Fiji Basins and ‘Lepetodrilus aff. schrolli MT’ from Mariana Trough. Later, further sampling and sequencing of material from Mariana Arc by Giguère and Tunnicliffe (2021) revealed highly similar COI sequences to ‘Lepetodrilus aff. schrolli MT’ (sensu Johnson et al. (2008)), extending its distribution to Mariana Arc vents including the Northwest Eifuku Volcano vent field (the type locality as per this work). Although Giguère and Tunnicliffe (2021) did not carry out a phylogenetic analysis using their sequences of this species (COI, MW807763-MW807765; 18S rRNA, MZ128922-MZ128923), this was done by Poitrimol et al. (2022) using the COI gene which confirmed that the Mariana Trough sequences from Johnson et al. (2008) (EU306431-EU306436) and the Mariana Arc sequences from Giguère and Tunnicliffe (2021) (MW807763-MW807765) fall into the same species-level clade. In both abovementioned phylogenetic analyses, ‘Lepetodrilus aff. schrolli MT’ (sensu Johnson et al. (2008)) was recovered sister to a clade containing L. schrolli and ‘Lepetodrilus aff. schrolli LF’ (sensu Johnson et al. (2008)). The lowest uncorrected sequence divergence for the COI gene amongst these three species was 3.1% (Johnson et al. 2008).

Lothar A. Beck attempted to describe these two Lepetodrilus species from the southwest Pacific, but they were never published before he passed away in 2020 (Chen and Sigwart 2023). Recently, many new species Beck recognised were formally published by Chen and Sigwart (2023), based on Beck’s unpublished manuscript, including ‘Lepetodrilus aff. schrolli LF’ sensu Johnson et al. (2008) which is now Lepetodrilus fijiensis Beck in Chen & Sigwart, 2023. ‘Lepetodrilus aff. schrolli MT’ (sensu Johnson et al. (2008)), however, remained undescribed until now and corresponds to Lepetodrilus marianae Chen, Watanabe & Tsuda, sp. nov. described herein. Although we were not able to study the previously sequenced specimens, we could examine Lepetodrilus specimens from NW Eifuku (Scripps Institution of Oceanography, Benthic Invertebrate Collection SIO-BIC M18546) collected together with those sequenced in Giguère and Tunnicliffe (2021) and they agreed morphologically with L. marianae sp. nov. Two new COI sequences were generated for this work from two specimens in paratype series 7 (NSMT-Mo 79484) and deposited in GenBank under the accession numbers OR640969-OR640970. All abovementioned sequences of L. marianae sp. nov. exhibited uncorrected pairwise genetic similarities above 99.2%.

Morphologically, L. marianae sp. nov. can be easily distinguished from other described Lepetodrilus species by its strong concentric sculpture, including its closest relatives (Johnson et al. 2008) L. schrolli and L. fijiensis L. Beck in Chen & Sigwart, 2023 (Beck 1993, Chen and Sigwart 2023). The only other Lepetodrilus species with similar shell profile and concentric sculpture is L. concentricus Linse, Roterman & Chen, 2019 from Antarctic vents on the East Scotia Ridge, but L. concentricus only exhibits one type of sculpture intermediate in strength between the two types seen in L. marianae sp. nov. (Linse et al. 2019) and, therefore, they are morphologically distinct.

Shinkailepas sp. nov. – Giguère and Tunnicliffe (2021): table S5

Shinkailepas sp. Manus Basin/Mariana Volcanic Arc – Poitrimol et al. (2022): fig. 6

Shell (Fig. 6): limpet form as adult with evidence of tighter coiling when juvenile, very large for genus. Shell dimensions of the holotype and paratypes are given in Table 3. Aperture oval, clear ventral columellar deck present posteriorly. Apex very posterior, protruding beyond posterior shell edge, slightly recurved to right side. Shell sculpture (Fig. 7C) finely cancellate with concentric ribs slightly stronger than radial ribs, minor protuberances occur where two ribs cross. Lateral profile of shell strongly curved. Shell microstructure (Fig. 7D) consisting of four layers: thin outermost dense homogenous layer followed by another thin granular homogenous layer which transitions to thick complex crossed lamellar layer then finally to thin simple prismatic layer. Protoconch corroded in all five adult specimens available for study.

Figure 6.  

Shinkailepas gigas Chen, Watanabe & Tsuda, sp. nov., habitus photographs of representative type specimens. A. holotype (SMF 373153), dorsal, ventral and lateral views, arrowhead on ventral view indicates the penis; B. Paratype 1 (NSMT-Mo 79486), dorsal, ventral and lateral views; C. Paratype 2 (SMF 373154), dorsal and ventral views; D. Paratype 3 (MNHN-IM-2019-34808), dorsal and ventral views. Scale bars: 5 mm.

Figure 7.  

Shinkailepas gigas Chen, Watanabe & Tsuda, sp. nov., scanning electron micrographs of paratype 4 (NSMT-Mo 79487). A. Radula overview; B. Close-up of marginal teeth; C. Shell sculpture; D. Fractured cross section of a shell showing microstructure. Scale bars: 500 μm (A, C), 50 μm (B, D).

External anatomy typical for the genus. Head large, broad, snout wide. Cephalic tentacles moderate in length. Males exhibit one large, swollen penis (Fig. 6A) just anterior of right cephalic tentacle. Mouth circular, oral disc papillated, oral lobes very large in size, extending laterally. Pallial margin swollen, simple, without tentacles. Foot circular, posterior half of epipodial fold serrated into approximately 50 paddle-like, broad projections. Operculum lacking in all five adults available for study.

Radula (Fig. 7A–B) rhipidoglossate, formula ca. 70-4-1-4-ca.70. Central tooth tall trapezoid, shaft thin, film-like, weakly developed with broad overhanging cusp, cutting edge smooth. Innermost laterals enlarged, three times as broad as rachidian, oblique in outline, shaft film-like; anterior edge rolled to form simple cusps lacking any serration. Second lateral narrower than rachidian, shaft sickle-like, with double overhanging cusps, upper cusp lacking serration, lower cusp shallowly serrated into about 10 cusps. Third lateral of similar breath to rachidian, twice as long as second lateral, cusp deformed, outer edge of shaft carrying broad lateral extension rolled inwards. Outermost lateral twice as large as third lateral, shaft divided into two columns, fusing anteriorly into one broad overhanging, simple cusp lacking serration. Inner marginals with semi-circular cusps serrated into 4-8 cusps, becoming more deeply serrated outwards. Outer marginals becoming much smaller in size with cusps serrated into several long denticles, gradually decreasing in size outwards.

A very large Shinkailepas species up to 23 mm in shell length with apex bent to the right side and protruding beyond the posterior shell margin. Shell sculpture finely cancellate, with concentric ribs only slightly stronger than radial ones.

The specific epithet gigas is Greek for ‘giant’; referring to the relatively large size of the species. Used as noun in apposition.

Specimens of S. gigas Chen, Watanabe & Tsuda, sp. nov. with identities confirmed by COI barcoding have been collected from the hydrothermal vents on Northwest Eifuku and Northwest Rota volcanoes on Mariana Arc (Giguère and Tunnicliffe 2021) and the Susu vent field in Manus Basin (Poitrimol et al. 2022).

Previously available COI sequences of this species include one from Northwest Eifuku (MW807775) and one from Northwest Rota (MW807774), Mariana Arc published by Giguère and Tunnicliffe (2021), as well as two from Susu vent field, Manus Basin (OM264371-OM264372) published by Poitrimol et al. (2022). One new COI sequence was generated for this work from paratype 4 (NSMT-Mo 79487) and deposited in GenBank under the accession number OR640971. We did not examine specimens sequenced by Giguère and Tunnicliffe (2021) or Poitrimol et al. (2022), but their COI sequences are highly similar to ours with the uncorrected pairwise percentage genetic similarities being 99.3% or above across all pairs.

Shinkailepas gigas Chen, Watanabe & Tsuda, sp. nov. was already recognised as an undescribed species by Giguère and Tunnicliffe (2021). Molecular phylogenetic reconstruction using the COI gene by Poitrimol et al. (2022) confirmed its genetic distinctness from described Shinkailepas species, but it remained unnamed until now. Its most closely related known species, Poitrimol et al. (2022), is Shinkailepas kaikatensis Okutani, Saito & Hashimoto, 1989 with a known distribution from vents on the Izu-Ogasawara Arc (Kaikata Seamount and Myojin Knoll), Okinawa Trough (Yoron Hole) and Mariana Arc (Kasuga 2 Seamount and East Diamante Seamount) (Fukumori et al. 2019). Though S. kaikatensis and S. gigas sp. nov. have, so far, not been sampled from the same vent fields, their distribution ranges overlap on the Mariana Arc and could potentially occur sympatrically. Although neither Giguère and Tunnicliffe (2021) nor Poitrimol et al. (2022) applied particular species delimitation tools, their distinctness is supported by a lowest known uncorrected COI genetic distance of 4.2% (Poitrimol et al. 2022). Morphologically, S. gigas n. sp. is clearly distinct from other named Shinkailepas species including S. kaikatensis by combining the following morphological features: 1) a finely cancellate sculpture where concentric ribs are slightly stronger than radial ones; 2) a very posterior apex bending slightly to the right and protruding beyond the posterior shell edge and 3) a very large size (Okutani et al. 1989, Sasaki et al. 2003, Fukumori et al. 2019). The only described congener with comparable size and sculpture is S. conspira Beck in Chen & Sigwart, 2023, but the apex of S. conspira is more anterior and central compared to S. gigas sp. nov. (Chen and Sigwart 2023). Furthermore, the central and inner laterals in S. gigas sp. nov. are exceptionally weakly developed for the genus. In all five adult specimens of S. gigas sp. nov. the operculum was lacking and, therefore, the juvenile operculum is likely naturally lost in this species during growth.

Holotype: SMF 373402, one whole individual with soft parts. Dimensions: Length: 2.7 mm; Height: 1.8 mm; Width: 1.6 mm (Fig. 8A-C).

Figure 8.  

Lyonsiella illaesa Machado & Sigwart, sp. nov., outer view of shell and internal tissues. 1A–C. Photomicrography of holotype (SMF 373402), right and left valves plus a dorsal view, respectively; 1D–M. Paratype (SMF 374320). 1D–F. Photomicrography of right and left valves plus a postero-ventral view, showing a natural deformity in the shell (nd) and a permanent opening (po) in the posterior margin; 1G–I. X-ray images showing the arrangement of the pallial cavity organs and visceral mass; 1J–M. Tomographic transverse sections of different parts of the specimen (yellow, red, green and orange squares). Abbreviations: aam, anterior adductor muscle; bt, byssal thread; ceg, cerebro-pleural (= circum-oesophagic glanglia); ct, ctenidia, dd/gc, digestive diverticula/gastric caecum; dm, detrital material attached; es, escutcheon; f, foot; h/hs, heart/haemocoel spaces; hg, hind gut; io, immature oocyte; is, inverted/contracted inhalant siphon; k, kidney; li, lithodesma; lp, labial palps; m, mouth; mm, mantle margin (ventral); mo, mature oocyte; nd, natural deformity in the shell; o, oesophagus; ov, ovary; pam, posterior adductor muscle; po, permanent opening in the shell; pprm, posterior pedal retractor muscle; pr, prodissoconch; sp, spikes; svm, sinuous ventral margin; te?, testis; tm, taenioid muscle, u, umbones. Scale bars: 1 mm (A–M).

Paratype: SMF 374320, one whole individual with soft parts. Dimensions: Length: 3.1 mm; Height: 2 mm; Width: 1.8 mm (Fig. 8D–M). This individual presents a natural deformity (nd) at the shell margin with subsequent repairs and a permanent opening (po) on the posteroventral margin, both probably caused by a teratological process during embryonic development. Similar deformities have already been observed in other species of verticordiid, such as Policordia uschakovi (Gorbunov, 1946), Policordia lisbetae Knudsen, 1970, Policordia ochotica Scarlato, 1981 and Lyonsiella subquadrata (Jeffreys, 1882) (see Knudsen (1970), fig. 89, Allen and Turner (1974), fig. 26b, Safonova and Krylova (2020), figs. 3 and 4b).

Shell: small (up to 3.1 mm in length), whitish to translucent, inflated, inequilateral; subrectangular, anterior margin rounded, posterior margin slightly truncate, ventral margin sinuous (svm/white arrows); inequivalve; umbones inflated, slightly prosogyrate; prodissoconch (200 ± 5 μm, n = 2), circular, smooth, preserved in the two individuals analysed (Fig. 8C, pr). Shell surface spiked (Fig. 8C, D and J, sp), densely occupied by series of long and pointed projections (= spikes) extending over all margins; small pustules or granules (= pustule-shaped spikes) in umbones and central part of shell, sometimes arranged radially; indistinct radial threads and concentric growth lines. Right valve overlapping left valve on dorsal and antero-posterior margins (Fig. 8B and C); lunule absent; shallow escutcheon (Fig. 8C, es); hinge edentulous; with lithodesma (Fig. 8L, li).

Anatomy:

Mantle margin: with two fused points, anteriorly forming short pedal gape and posteriorly forming siphonal apertures; posteroventrally, mantle margin fusion (Fig. 8J–M, mm) involving inner folds only (Type A) (Yonge 1982); absence of fourth pallial aperture. No evidence of arenophilic glands (= radial mantle glands) and/or arenophilic secretions in outer surface of the shell. Perhaps functions of camouflage, strengthening thin shells and anchoring/stability in soft substrata, usually associated with such glands (Prezant 1985, Machado et al. 2017, Morton and Machado 2019), are performed here by the thousands of spikes on the outer surface of the shell.

Siphons: Separated; inhalant siphon inverted (Fig. 8H, is), probably cone-shaped; both surrounded by small tentacles at base, ~ 8 in inhalant and ~ 3 in exhalant siphon, only a single row of tentacles was observed. Similar to other carnivorous anomalodesmatan, L. illaesa sp. nov. can be also characterised as ‘lie-in-wait’ micro-predator (Machado et al. 2017, Morton et al. 2019, Morton and Machado 2019), that is camouflaged within its habitat by detrital material attached to its shell by its thousands of spikes and capturing prey by eversion of the cone-shaped inhalant siphon.

Ctenidia: Reduced, non-plicate and horizontally aligned (Fig. 8H, J and K, ct); incomplete, with only inner demibranch, moderately shorter filaments in comparison with other lyonsiellids (e.g., Lyonsiella subquadrata, Lyonsiella fragilis Allen & J. F. Turner, 1974) and range in number from 8 to 10.

Labial palps: Non-lamellate, outer and inner palps short, unfused and elongated tips forming two wing-like lateral flaps (Fig. 8G, lp).

Musculature: Posterior and anterior adductor muscles present, isomyarian; with posterior and anterior pedal retractor muscle; posterior pedal retractor muscle bifurcated and dorsally attached to the shell close to the posterior adductor muscle (Fig. 8G, pprm); presence of taenioid muscle (= inhalant siphon retractor muscle) (Fig. 8G, tm).

Foot: Small, unpronounced heel (Fig. 8G and K, f); presence of a single byssal thread (Fig. 8K, bt).

Digestive system: Funnel-shaped mouth opening into a long oesophagus (Fig. 8M m, o) that enters into the anterodorsal portion of the stomach (Fig. 8L, st); stomach small, rounded, no crystalline style sac, no prey inside, surrounded dorsally, anteriorly and laterally by the gonads and the digestive gland; digestive diverticula with large gastric caecum (= blind ending tubules on both sides of the stomach walls) (Fig. 8L and M, dd/gc).

Organs of visceral mass: Pericardium/heart area well delimited (Fig. 8H, h/hs); paired kidneys restricted to the most posterior part of the body close to the posterior adductor muscle, posterior pedal retractor muscle and hind gut (Fig. 8H and J, k, pprm, hg). A lacunal system, formed by haemocoel spaces, is present in the posterior portion of the visceral mass, associated with the kidney and pericardium (Fig. 8H, h/hs). This system is commonly reported for members of Verticordioidea and appears to be an exclusive feature of this superfamily, having been associated with an important prey capture mechanism (Morton 1984).

Reproductive system: Probably hermaphroditic, ovary well visible (> 30 mature oocytes counted, ~ 150 μm in diameter) (Fig. 8H, I, K and L, ov); at least two stages of gametogenesis observed, i.e. immature oocytes - small cells attached in the wall of the ovarian follicle and mature oocytes - larger and usually free in the ovarian lumen (Fig. 8H, I, K and L, io, mo); testis relatively small, oval and probably located in the anteroventral portion of visceral mass close to the ventral wall of the stomach (Fig. 8L, te?). It is also worth highlighting the possibility of L. illaesa sp. nov. having a brooding behaviour, since it presents some indirect evidence, for example, larval prodissoconch size, small dimensions of the body (miniaturisation) and the possibility of mature oocytes are, in fact, encapsulated oocytes (post-fertilisation). 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 verticordiid Trigonulina ornata d'Orbigny, 1853 (Morton et al. 2019).

Nervous system: Cerebro-pleural (Fig. 8M, ceg), visceral (Fig. 8H, vg) and pedal ganglia present; statocysts were not observed associated with the latter.

Shell whitish to translucent, thin, inflated, subrectangular, ventral margin sinuous; outer surface ornamented by spikes (> 1000) covering entire shell surface, except for prodissoconch (pr); umbones inflated and slightly prosogyrate; radial lines absent; hinge edentate; posterior pedal retractor muscle bifurcated; presence of taenioid muscle; ctenidia reduced, with only inner demibranch, horizontally aligned; absence of crystalline style sac; paired kidney restricted to the most posterior part of the body; presence of a single byssal thread; probably hermaphrodite with large oocytes.

Relative to the absence of any damage caused during the morphological description. The Latin word illaesa [in (“non”) +‎ laesa (“lesion”, “wounded”, “damaged")]. For the first time, a new species of mollusc is described in detail (including shell and internal tissues) without the use of any invasive tool.

Known only from the Aleutian Islands, off Alaska, North Pacific. Bathymetric range: 5,100–5,318 m, a new record for the genus previously recorded at 4,429 m in the North Atlantic (see Poutiers and Bernard (1995)).

This species was compared with all morphologically similar species of the genus and differs from the other Pacific species, such as Lyonsiella quaylei F. R. Bernard 1969 (Coan and Valentich-Scott 2012, plate 326), Lyonsiella magnifica Dall, 1913 (holotype USNM 266802), Lyonsiella pacifica Dall, 1908 (holotype USNM 110583), Lyonsiella quadrata Hedley, 1907, Lyonsiella aotearoa Dell, 1995 and others in having an outline more rectangular, a ventral margin sinuous, absence of radial lines and umbones more inflated and central (= less prosogyrate). These same features were also used to differentiate it from the Atlantic species Lyonsiella frielei Allen & Turner 1974 (holotype MCZ 272672), Lyonsiella abyssicola (Machado and Passos 2022, fig. 3j, MCZ 272772), Lyonsiella subquadrata (syntype USNM 63238, MCZ 272774, 348035) and all its possible shell variations illustrated by Allen and Turner (1974), figs. 1–2, 26–27. Regarding anatomy of new species, some features, such as the number of ctenidia filaments and siphonal tentacles, posterior pedal retractor muscle bifurcated, a single byssal thread, absence of crystalline style sac, paired kidney restricted to the most posterior part of the body, can also be used to differentiate it from their congeners, although the first two may be associated with intraspecific variations in individual size and shape, perhaps related to age.

Holotype, NHMW-CR-29747, DZMB 10099, adult female, 7.3 mm, GenBank number OR839896. Figs 9, 10, 11, 12.

Figure 9.  

Lepechinella naces Lörz & Engel, sp. nov., NHMW-CR-29747, holotype, adult female, 7.3 mm. A. Habitus, right lateral view; B. Antenna 1; C. Antenna 2; D. Right mandible; E. Maxilla 2; F. Maxilliped; G. Hypopharynx; H. Maxilla 1; I. Left mandible. Scale bars: 1 mm (A), 0.1 mm (B–H).

Figure 10.  

Lepechinella naces Lörz & Engel, sp. nov., NHMW-CR-29747, holotype, female, 7.3 mm. A. Pereopod 1; B. Detail of pereopod 1 palm; C. Pereopod 2; D. Pereopod 3; E. Pereopod 4; F. Pereopod 5; G. Pereopod 6; H. Pereopod 7. Scale bars: 0.1 mm.

Figure 11.  

Lepechinella naces Lörz & Engel, sp. nov., NHMW-CR-29747, holotype, female, 7.3 mm. A. Uropod 1; B. Uropod 2; C. Uropod 3; D. Pleopod 2; E. Telson. Scale bars: 0.1 mm.

Figure 12.  

Lepechinella naces Lörz & Engel, sp. nov., NHMW-CR-29747, holotype, female, 7.3 mm. Habitus, right lateral view. Photographed in the lab via a Keyence 6000 microscope. Scale bar: 1 mm.

Body setose. Head with rostrum slightly curved, 20% of length of first peduncle art of A1; first cephalic tooth long, slender, longer than rostrum; second cephalic tooth acute. A1, almost reaching length of A2, shorter than length of body; first article 50% length of second art, bundle of setae at distal end; third art half the length of first art; flagellum 25 art. A2, art3, 4 and 5 with setae, art5 very slender, longer than art1–4 combined, with fourth art 60 % length of fifth art; flagellum 18 art.

Md with incisor process dentate, lacina mobilis dentate, molar triturative, palp broken off. Mx1, inner plate with two plumose setae; outer plate with 11 dentate spine teeth; palp second art distally expanded and slightly truncate, distal margin with 10 blunt spine teeth. Mx2, inner plate with one plumose seta, inner plate narrower and shorter than outer. Mxp, inner plate slender, distally rounded, distal setae; outer plate reaches to the last third of second art of palp, distal part of inner margin with short thick spines apically ending in long spines; palp four art, second art twice the length of third art. Hypopharynx, bilobate, inner lobes well developed extending to half of outer lobe.

Prn and Pleon, Prn1 with two upright teeth. Prn2–7 and pleon dorsally carinate, each carina terminating in a subacute, posteriorly directed tooth.

P1, coxa not bifid, anterodistally produced, distal margin convex, serrate; basis as long as ischium, merus and carpus combined; basis to propodus setose, palm half the length of posterior margin, dactylus smooth. P2, coxa marginally setose, tapering distally, anterior margin convex; propodus slender, slightly shorter than basis, palm almost half the length of posterior margin; dactylus small setae.

P3 and P4, similar in shape, coxae slightly bifid, lobes same length. P5 and P6, coxa anterior lobe pointed ventrally, setae on all segments. P7, coxa rounded, basis to propodus setose.

Ep convex posteriorly, each with prominent postero-distal tooth.

Urosome Urosomite 1 strongly produced dorsally, urosomite 3 produced extending to more than half of telson length.

U1, peduncle and outer ramus subequal; inner ramus broken; strong spines on peduncle and rami. U2, outer ramus slightly shorter than inner ramus, subequal in length to peduncle; peduncle and rami with strong spines. U3, peduncle very short, quarter of length of outer ramus; inner ramus similar length to outer ramus. T, cleft 30 %, lobes each with apical spine, telson length equals length of spine.

Variation: The paratype NHMW-CR-29748, juvenile, 3.2 mm, GenBank number OR839894 (Fig. 13), morphologically differing from the adult (Figs 9, 10, 11, 12) in the absence of teeth on pereonite 1, weakly-developed carinae on the pereonites and pleonites. Morphological characters are known to vary between age and stages of growth amongst lepechinellid amphipods (Barnard 1973, Thurston 1980, Lörz et al. 2020). The non-type specimen NHMW-CR-29749, juvenile, 3 mm, collected at the same station as the holotype and paratype, was heavily damaged, but a barcode analysis (GenBank number OR839895) confirmed 100% similarity to the holotype.

Figure 13.  

Lepechinella naces Lörz & Engel, sp. nov., NHMW-CR-29748, paratype, juvenile, 3.2 mm. Habitus, right lateral view. Photographed in the lab via a Keyence 6000 microscope. Scale bar: 1 mm.

Lepechinella naces Lörz & Engel, sp. nov. is characterised by a setose body, antenna subequal in length, shorter than body, two dorsal teeth on pereonite 1, coxa 1 tapering non-bifid, coxa 7 being rounded and the telson being cleft 30%.

The specific epithet naces is a noun in apposition, referring to the high seas North Atlantic Current and Evlanov Sea Basin (NACES), a marine protected area (MPA), which covers nearly 600,000 km².

Lepechinella naces Lörz & Engel, sp. nov. is morphologically closest to Lepechinella grimi Thurston, 1980 (Thurston 1980), Lepechinella occlo Barnard, 1973 (Barnard 1973), Lepechinella pangola J.L. Barnard, 1962 (Barnard 1962) and Lepechinella victoriae Johansen & Vader, 2015 (Johansen and Vader 2015); these five species bear two distinct extensions on pereonite 1. Table 4 lists differential characters.

The closest hits, when blasting the COI sequences of L. naces sp. nov. in BOLD and GenBank, were a Lepechinella specimen not identified to species level, collected in the Kuril Kamchatka Trench (Jażdżewska and Mamos 2019) with 6% difference and L. grimi from the North Atlantic (Lörz et al. 2020) with 15% difference.

A further species of Lepechinella, which we identified as Lepechinella sp. (NHMW-CR-29750, GenBank number OR839893) was collected at the same station as L. naces sp. nov. This specimen morphologically resembles L. skarphedini, which has not been genetically sequenced to date. It differed from L. naces sp. nov. by comparison of the COI segment by more than 20%.

Composition: One valid species, which is described herein; Cuniculomaera grata Tandberg & Jażdżewska, sp. nov.

Small round eyes. Accessory flagellum 8-articulate. Pereopod 2 propodus suboval, palmar corner not sharply defined, dactylus smooth and sharp. Epimeral plates smooth, epimeral plate 3 with sharp tooth. Uropod 3 elongate, rami of similar length, covered by bushy setae. Telson deeply and widely cleft.

Cuniculomaera is a compound noun formed from the Latin second-declension noun cuniculus (burrow) and the suffix -maera from Maera, the type genus of the family Maeridae. Gender: feminine.

The decision to erect a new genus for Cuniculomaera grata Tandberg & Jażdżewska, sp. nov. (described below) comes from it differing in diagnostic characters from all initially eligible genera within the family Maeridae Krapp-Schickel, 2008. The placement of the genus into Maeridae follows the discussion in Krapp-Schickel (2008), where she separates the Ceradocus-Elasmopus-Maera-group from Melitidae Bousfield, 1973, based on the equiramous uropod 3 in this group compared with the parviramous uropod 3 in Melitidae. The use of the defining morphological characters of uropod 3 is kept by Lowry and Myers (2013), who also keeps Maeridae separate from the morphologically quite similar Hadziidae S. Karaman, 1943 due to the morphology of the gills. It should also be noted that Hadziidae are exclusively freshwater species. The gills of Cuniculomaera grata sp. nov. are not stalked (rather “normal” for marine species), again placing the new genus within Maeridae.

The equiramous uropod 3 of Cuniculomaera gen. nov. can be observed in Fig. 14. Sadly, uropod 3 was lost in the specimen that was sampled. Placing it in the Maera Leach, 1814 s. l. group (sensu Krapp-Schickel 2008) comes from it differing from Ceradocus A. Costa, 1853 in its epimeral plate 3 not being serrated (it is smooth, with a clear tooth), the shape of the telson (the lobes being slender and with two small teeth compared to the one tip on each lobe “Ceradocus-telson”) and the dorsal shape of the urosome which is smooth compared to the “can have teeth” of Ceradocus. It differs from Elasmopus A. Costa, 1853 by having a long accessory flagellum (not short as for Elasmopus) and in the shape of the mandibular palp article 3 (the Elasmopus article is falcate, Cuniculomaera has this palp straight) and epimeral plate 3 posterior corner being a sharp tooth compared to the Elasmopus blunt corner.

Figure 14.  

Burrows where Cuniculomaera grata Tandberg & Jażdżewska, sp. nov. is suggested to live. Photos from AleutBio expedition. A. Amphipod in last of burrow openings; B. Zoom in of amphipod from A.

Maera s. l. was split into several genera by Krapp-Schickel (2008); the present new genus can be separated from these by the combination of the accessory flagellum, eye-shape, pereopods 1 and 2 shapes, epimeral plate 3 posterior corner and telson-shapes. It also differs in its depth range, albeit this is not a diagnostic character.

The obtained sequence was positively checked as belonging to Amphipoda against the Barcode of Life Data System (BOLD) and GenBank databases; however, with only ca. 80% similarity to published sequences. The closest relative in GenBank was Uristes gigas Dana, 1852 (78.97% similarity, acc. No. MH825809.1) while in BOLD: Wimvadocus torelli (Goës, 1866) (79.97%, sample ID: BSM08T16-01, record not available in GenBank). The number of publicly available sequences of Maeridae is relatively low (164 sequences of which 62 belong to only two species), while the family is represented by 423 species grouped in 48 genera (Horton et al. 2023). A phylogenetic analysis was not conducted; only the barcode of the new species is provided for future use.

Maeridae: Brandt et al. (2022): 107, Table 5.18; p 109, fig. 5.60M.

“maerid amphipod”: Brandt et al. (2022): 131, text.

Maera sp.: Brandt et al. (2023): 4, text.

“maerid amphipod”: Brandt et al. (2023): 4, fig. 2.

Body dorsally smooth (Fig. 15), elongate with short coxae. Length 24 mm.

Figure 15.  

Cuniculomaera grata Tandberg & Jażdżewska, sp. nov., male holotype (SMF-61334). Habitus photography. Scale bar: 5 mm.

Head (Fig. 16C) shorter than deep, cephalic lobes rounded, eye small (0.5x height of A1 insert) and roundish. A1 (Figs 15, 16A) as long as body; art2 longer than art1 which is longer than art3; acc flag 8-articulate and ¼ of flagellum length, all art with 2 short setae; flagellum with approximately 40 art, short thin setae on each. A2 (Fig. 16B) half the length of A1, art4 and 5 subequal in length, both with several thin setae; flagellum 15-articulate, all art with several short setae. Lbr (Fig. 16D) symmetric. Md (Fig. 16E, F) molar triturative; palp 3-articulate, art2 longer than art3 which is longer than art1, art3 is straight, art2–art3 setose; incisor smooth and bifurcate; 11 raker setae decreasing in thickness from incisor towards molar; lacinia mobilis on right Md. Mx1 (Fig. 16G, H) inner plate subtriangulate, bushy setae distally; outer plate elongate and blunt with 7 cusped setae distally, palp 2-articulate with 6 long and 5 short straight setae distally on art2. Mx2 (Fig. 16I) inner and outer lobe subequal, inner lobe strongly setose along inner margin. Lbi (Fig. 16J) slightly notched, symmetrical. Mxp (Fig. 16K) inner plate totally separate, distal margin concave and heavily setose; outer plate reaching ⅔ of palp art2 sensory setae along distal and inner margin; palp art3 4x as long as art2, heavily setose inner margin; dactylus ½ art3 length.

Figure 16.  

Cuniculomaera grata Tandberg & Jażdżewska, sp. nov., male holotype (SMF-61334). A. Antenna 1; B. Antenna 2; C. Head; D. Labrum; E. L mandible; F. R mandible; G. R Maxilla 1; H. L maxilla 1; I. Maxilla 2; J. Labium; K. Maxilliped. Scale bars: 1 mm (A–C), 0.5 mm (D–K).

Pereon: All coxae shown on Fig. 15 (habitus photo). P1 (Fig. 17A and C) C1 (Fig. 16C) with small rounded extension on distal anterior corner; basis straight, anterior margin with long setae; ischium and merus short with distal margins setose; carpus suboval, sensory setae (Fig. 17C) along posterior margin; propodus suboval, palmar corner weakly defined by strong setae, palm and hind margin strongly setose, palm oblique; dactylus strong and sharp. P2 (Fig. 17B and C) slightly larger than P1; C2 (Fig. 16C) rounded with anterior margin bulging, smooth distal margin; basis straight; ischium and merus short; carpus subtriangulate heavily setose with sensory setae (Fig. 17C) along posterior margin; propodus suboval, palm oblique and weakly serrate with palmar corner defined by 3 large setae, hind margin and palm with sensory setae, along hind margin in tufts; dactylus sharp, inner margin with 6 short setae. P3 (Fig. 17D) and P4 (Fig. 17E) straight long and thin, longer than P1 and P2, dactyli with sensory setae. P5–P7 only known from in situ photo (Fig. 14) and video, where they are clearly longer than P1–P4, straight and slim.

Figure 17.  

Cuniculomaera grata Tandberg & Jażdżewska, sp. nov., male holotype (SMF-61334). A. Pereopod 1; B. Pereopod 2; C. Seta on posterior margin of carpus, P1 and P2; D. Pereopod 3; E. Pereopod 4; F. Epimeral plates 1–3; G. Telson; H. Uropod 1; I. close-up of U1 peduncle distal portion. Scale bars: 0.5 mm.

Pleon: Ep1–Ep3 (Fig. 17F) all smooth, Ep1 posterodistal corner with rounded extension, Ep2 posterodistal corner with small rounded tooth, Ep3 posterodistal corner medium-sized sharp tooth.

Urosome: Smooth (Fig. 15), U1 (Fig. 17H) peduncle with spur 1/6 length of rami, rami of equal length, slim, short setae along outer margins. U2 (Fig. 15) peduncle half length of U1 peduncle, rami similar length to U1 rami. U3 (Fig. 14) longer than U1 and U2, rami similar length, wide and setose. T (Fig. 17G) deeply (80%) cleft, gaping, lobes thin with slightly concave inner margin, two short teeth at tip, one strong seta at each tip.

Colour in vivo (Fig. 14): light pink.

As for the genus.

The Latin feminine noun grata, meaning "favourite", alludes to the term "favourite burrows" given originally to the strange sediment constructions recorded on the sea bottom by the members of AleutBio expedition while watching and analysing the video footages from the Bering Sea. Now we know they were constructed by the presently-described species, so we call it favourite as well.

See discussion for the genus.

"undescribed Pseudionella sp.": Landschoff et al. (2018): 2, 12: figs. 6D, 14.

Female holotype (Figs 18, 19) body length 3.4 mm, maximum width 1.8 mm, head length 0.5 mm, head width 0.7 mm, pleon length 1.1 mm. Body tear-drop-shaped (Fig. 18B and C, Fig. 19A and B), approximately symmetrical, head slightly sinistrally rotated (< 5°). Very small patches of pigment present on some Prn (Fig. 19A).

Figure 18.  

Live image of Pagurus fraserorum Landschoff & Komai in Landschoff et al., 2018 and Pseudionella pumulaensis Williams & Landschoff, sp. nov. A. Dorsal view of P. fraserorum with inflated left branchial chamber; B. Left lateral view with branchial chamber showing P. pumulaensis sp. nov.; C. Close-up view of B. Scale bars: 2 mm (A, B), 1 mm (C).

Figure 19.  

Pseudionella pumulaensis Williams & Landschoff, sp. nov., adult female holotype (SAMC A096401). A. Habitus, dorsal view; B. Habitus, some eggs shown in dashed lines, ventral view; C. Right barbula; D. Pleon, right lateral view; E. Right antennule, antenna and mouthparts, ventral view; F. Right oostegite 1, internal view; G. Right oostegite 1, external view; H. Right maxilliped, external view; I. Left pereopod 1; J. Left pereopod 7. Abbreviations: A1 = antennula, A2 = antenna, Mo = mouthparts, Pl1–Pl5 = pleomeres 1–5, U = uropod. Scale bars: 500 µm (A, B), 250 µm (C, D, F, G), 50 µm (E, H–J).

Head subquadrate (Fig. 19A) with slight medial indentation at anterior end, narrow frontal lamina extending slightly beyond lateral margins of head. Small eyes near posterolateral corners of raised lamina edge. Barbula with two pairs of small, smooth rounded lobes (Fig. 19C). A1 (Fig. 19E) of three art each, extending beyond anterior margin of head; A2 (Fig. 19E) of three art each, but basal art broadly rounded and fused with head (see Remarks); all art of A1 and A2 with spinous scales and distal setae. Mxp (Fig. 19H) anterior lobe broad, rounded, with unarticulated palp with few large setae and many fine setae, lateral edge of lobe setose; posterior lobe with small rounded spur.

Prn (Fig. 19A) of seven Prn, broadest across Prn3, tapering anteriorly and posteriorly. Small coxal plates on sides of pereomeres all similar, but larger on left side of body; dorsolateral bosses on Prn1–Prn4. First oostegite anterior lobe ovate, posterior lobe subtriangular, internal ridge smooth (Fig. 19F and G). Oostegites 3–5 with some minute circular tubercles; oostegite 5 with fringe of setae on posterior margin (Fig. 19B). P1–7 (Fig. 19I, J) slightly increasing in size posteriorly and of similar morphology, small curved dactylus, ovate propodus indistinctly separated from triangular carpus, small triangular merus, elongate ischium and subquadrate basis; all art with spinous scales, propodus with few small setae on anterolateral margin, carpus with stout setae at anterior tip (Fig. 19I and J).

Pleon (Fig. 19B and D) of six Pl. Pl1–Pl5 with uniramous, digitiform Plp (Fig. 19B and D), first two Plp with indentation giving appearance of biramous morphology, but each a single lobe (possible fusion of endopod and exopod); uniramous rounded lateral plates (Fig. 19B and D); lateral plates and Plp reduced in size from anterior to posterior. Plt (Fig. 19B and D) with sixth pair of lateral plates projecting laterally and pair of large broad, distally rounded uniramous uropods.

Eggs (Fig. 19B) approximately 195 in number, a few potentially lost in transfer, 150.3 ± 9.9 µm in diameter (n = 30).

Male paratype (allotype) (Fig. 20) body length 1.3 mm, maximum width 0.7 mm, head length 0.2 mm (not including Prn1), head width 0.4 mm, pleon length 0.3 mm. Body suboval-shaped, squat. Small, irregular patches of dark pigmentation on nearly all Prn.

Figure 20.  

Pseudionella pumulaensis Williams & Landschoff, sp. nov., adult male paratype (allotype) (SAMC A096402). A. Habitus, dorsal view; B. Habitus, ventral view; C. Left antennula, antenna, mouthparts and pereopod 1, ventral view; D. Left pereopod 7 and pleon, ventral view. Abbreviations: A1 = antennule, A2 = antenna, Mo = mouthparts, P1 = pereopod 1, P7 = pereopod 7, Pl1–Pl5 = pleomeres 1–5. Scale bars: 250 µm (A, B), 50 µm (C, D).

Head fused with Prn1, anterior margin of head broadly rounded (Fig. 20A), irregularly-shaped eyes near posterolateral margin. A1 of three art each; A2 of five art each, extending slightly beyond margin of head; A2 and A1 with few spinous scales and distal setae (Fig. 20C).

Pereon of seven Prn, broadest across pereomere 4, tapering anteriorly and posteriorly. Lateral margins of Prn1–3 directed anteriorly, Prn4–7 directed posteriorly. P1 (Fig. 20C) largest, slightly decreasing in size posteriorly; all art distinct, curved dactylus with minute setae, ovate propodus, subquadrate carpus, elongate merus and ischium, small subquadrate basis; all art with spinous scales, propodus scales and spines adjacent to dactylus plus few setae on anterolateral margin, carpus with stout setae at anterior tip; P7 (Fig. 20D) similar in morphology to P1, except dactylus shorter and carpus more triangular in shape.

Pleon (Fig. 20D) of six Pl, markedly narrower than pereon, Pl tapering posteriorly, all Pl distinctly segmented and bearing lateral plates, Pl1­–4 with pleopods indistinctly separated from lateral plates, Pl5 with broad, rounded lateral plates; no mid-ventral tubercles (Fig. 20D). Plt (Fig. 20D) notched medially with anal cone, produced distolaterally into rounded lobes, with scales and setae; Urp absent.

Female body nearly straight, barbula with two small, smooth lobes on each side, all pleopods uniramous. Male head fused with pereomere 1, antennulae and antennae of 3 and 5 articles, respectively.

The specific epithet pumulaensis refers to the locality of Pumula in KwaZulu-Natal, South Africa, where the species was first discovered. The word Pumula is Zulu and means "a place of rest".

KwaZulu-Natal, east coast of South Africa (Indian Ocean); rocky subtidal reef.

Host: Pagurus fraserorum Landschoff & Komai in Landschoff et al. (2018) (Crustacea, Decapoda, Anomura, Paguridae Latreille, 1802), a hermit crab described from KwaZulu-Natal, South Africa. Parasite location on host: Branchial chamber (gill-parasitic). See Fig. 18 and Landschoff et al. (2018), page 14.

Only one out of nine specimens of Pagurus fraserorum Landschoff & Komai in Landschoff et al. (2018) was found parasitised by P. pumulaensis sp. nov. (11% overall prevalence). An additional specimen of P. fraserorum was reported by Landschoff et al. (2018) to have another branchial parasitic isopod (provisionally identified as Pseudionella sp.); unfortunately, that specimen no longer exists.

Formerly, Pseudionella was known to contain five species, which parasitise diogenid (1 species) and pagurid (4 species) hermit crabs from the South Pacific Ocean, North Pacific Ocean, North Atlantic Ocean, Caribbean Sea and South China Sea (Shiino 1949, Adkison and Heard 1978, Bourdon 1979, Boyko and Williams 2001, An et al. 2013). The new species of Pseudionella described herein parasitising Pagurus fraserorum Landschoff & Komai in Landschoff et al. (2018) is the first reported from the genus on hermit crabs from the Indian Ocean.

Pseudionella pumulaensis Williams & Landschoff, sp. nov. can be distinguished from the previously described species (P. akuaku Boyko & Williams, 2001, P. attenuata Shiino, 1949, P. deflexa Bourdon, 1979, P. markhami (Adkison & Heard, 1978) and P. spiropaguri An, Li & Markham, 2013), based on several characters. In contrast to females of P. akuaku, P. attenuata, P. deflexa and P. markhami, which are highly asymmetrical (dextral or sinistral deflexion of the head), P. pumulaensis and P. spiropaguri are nearly straight. In overall body form of females and males, P. pumulaensis and P. spiropaguri appear most similar, but can be distinguished, based on the following characters: barbula morphology (two small, smooth lobes on each side in P. pumulaensis vs. three lobes with digitate tips on each side in P. spiropaguri), female pleopod morphology (all uniramous in P. pumulaensis vs. first three biramous in P. spiropaguri), male antennae morphology (antennules and antennae of 3 and 5 articles, respectively in Pseudionella pumulaensis vs. 3 and 4 articles in P. spiropaguri) and male head fusion (fused with pereomere 1 in P. pumulaensis vs. separated in P. spiropaguri).