Re-description of Parasphaerosyllisindica Monro, 1937 (Annelida, Syllidae), with the establishment of a new species from western Mexico

Abstract Background Parasphaerosyllis Monro, 1937 is a syllid genus, currently composed of four species: P.indica Monro, 1937 from the Arabian Sea, P.uschakovi (Chlebovitsch, 1959) from the Kurile Islands, P.ezoensis Imajima & Hartman, 1964 from Japan and P.malimalii Capa, San Martín & López, 2001 from the Pacific coast of Panama. The distribution of P.indica is circum-tropical to temperate waters, but the presence of species complexes has been suggested. In order to clarify the distribution of P.indica in many areas of the world, a re-description, based on examination of the type material, is required as a first step to a better understanding of its diagnostic features. New information Parasphaerosyllisindica is re-described, based on holotype examination, a new species is established from the Gulf of California and Parasphaerosyllismalimalii is reported for the first time since its description in 2001. Parasphaerosyllisirregulata sp. nov. is distinguished from its congeners by the following features: 1) Palps are free at their base; 2) Two types of dorsal cirri are present: spherical to bulbous and moniliform cirri; 3) Both types of cirri are distributed irregularly. A spherical/bulbous and moniliform cirrus may appear together within the same segment (asymmetrical segment) or only a spherical/bulbous cirrus may appear in several consecutive segments (not alternating as occurs in congeners); 4) The spherical/bulbous cirri may have distal knobs with 1–3 terminal articles; and 5) Bidentate falcigers with short, sub-triangular blades with a proximal tooth slightly larger that the distal one. A taxonomic key to species of Parasphaerosyllis species is included.


Fieldwork
Specimens of the new species described in the present study were collected in artificial reefs from La Paz Bay in the Gulf of California, Mexico.Methods are documented in de León-González and Balart (2016).An area of 0.20 × 0.20 m on a lateral wall of artificialreef structures was sampled (0.04 m ; total sampled area by survey 0.4 m ).This area was fragmented with chisel and hammer and the fragments transferred to poly-ethylene bags in situ.Sorting and taxonomic analysis of formalin-fixed worm material was performed in the Laboratory of Biosystematics (UANL).Specimens of Parasphaerosyllis malimalii were collected by scraping rocks covered by coralline algae from the intertidal area of Nayarit and Jalisco (Central West of Mexico).

Identification
Observations and body measurements were taken using an Olympus BX51 microscope with differential interference contrast (DIC).Photographs were taken with an attached Nikon D610 digital camera.Drawings were made with a camera lucida.A specimen was dehydrated in a series of progressive concentrations of hexamethyldisilazane (HMDS).Once air-dried, the specimen was mounted on aluminium stubs and gold-coated for observation in a JEOL JSM-6010Plus-LA scanning electron microscope at the Scanning Electron Microscopy Laboratory (LMEB), ECOSUR-Chetumal, Mexico.

Description
Holotype incomplete posteriorly, 5 mm long, 0.4 mm wide on proventricle, 68 chaetigers.Body subcylindrical, ventrally flattened (segments 15 and 16 from anterior end remarkably wider than rest of body, perhaps due to manipulation caused by strong pressure on slide cover, because proventricle is broken and pharynx flattened).Body brown-yellowish, without pigmentation pattern.All cirriform annulated appendages deeply coiled (Fig. 1A).Prostomium pentagonal, wider than long.Four lensed eyes in trapezoidal arrangement, eyes from the anterior pair larger and more separate than posterior pair of eyes (Fig. 1A).Right anterior eye divided into two lobes, appearing to have two fused eyes.Eyespots absent.Palps stout, triangular, slightly directed towards the ventral side, similar in length to prostomium, only fused in a small part of base.Median and right antennae lost.The median antenna preserves the cirrophore and the first annulation only, which arises from posterior end of prostomium, between posterior pair of eyes (Fig. 1A).Left lateral antenna inserted on anterior margin of prostomium, longer than prostomium with 7 articles of different sizes in irregular arrangement (Fig. 1 A).Peristomium shorter than subsequent segments, folding on posterior part of prostomium (Fig. 1A).Peristomium with two pairs of tentacular cirri: dorsal ones with 24 articles each, right ventral cirrus with 14 articles, left ventral cirrus incomplete, with 7 articles.First pair of dorsal cirri with 24 articles each.Dorsal cirri from chaetigers 2 to 17 with 20-24 articles, not alternating in length.Mid-body dorsal cirri with 20-22 articles and posterior cirri with 15-18 articles.The first bulbous cirrus appears on chaetiger 15 on left side, whereas on the right side appears on chaetiger 17.From chaetiger 17 backwards, dorsal cirri alternate regularly, one by one: an annulated cirri and a bulbous one.Bulbous dorsal cirri elongate, cirrophore not visible (Fig. 1B).Base of bulbous cirri thin, enlarged medium part and a small unarticulated knob at the end (Fig. 1B-E).Bulbous cirri with curved diagonal fibrous lines, being more evident on some cirri than others.Some annulated cirri broken (incomplete) or fully removed (only scars are evident).Parapodial lobes slightly wide on base, with one or two notorious acicular papillae.Ventral cirri digitiform, shorter or similar in length than parapodial lobe.Anterior parapodia with about 10 compound heterogomph chaetae (6 on chaetiger 1), number diminishes gradually through the body to 6 on posterior segments.Falcigers dorso-ventrally decreasing in length, bidentate blades with thin spines on its internal margin, shafts with small and fine distal spines.Falcigers from anterior chaetigers with blades longer and thinner than posterior ones (Fig. 1F-G).Size proportion between dorsal-most versus ventral-most blades: anterior one 2.0 to 2.1, posterior one 1.5 to 1.6.Simple acicular chaetae, dorsal or ventral, not observed.
Anterior parapodia each with two slender aciculae: one straight, pointed and other distally curved, acute.Mid-body and posterior segments with one acicula per parapodium, larger and thicker than anterior ones, distally curved.Pharynx occupying the space of about seven segments, pharyngeal tooth located anteriorly, pointed, acute, yellowish.Proventricle broken, longer than pharynx, extending through 8-9 segments, with about 22 muscle cell rings, with distinct mid-dorsal line.From chaetiger 62 backwards, forming a male stolon (damaged).

Diagnosis
Palps fused at their bases.Peristomium shorter than following segments.Dorsal cirri from mid-body bulbous with a long distal end and terminal knob, alternating with long and articulate cirri in a regular pattern (one by one).Bidentate falcigers with long blades, proximal tooth shorter than distal one.

Distribution
Parasphaerosyllis indica was described from the coast of Oman to 13.5 m depth.It has been reported in many localities around the world.Unfortunately, many of these reports include only a brief mention or just the name within a list of species or tables of ecological analyses and compendia, making its status unverifiable: Hartman (1954) (Eniwetok Atoll); Reish (1968) Marshall Islands); Amoreux et al. (1978) Aguado et al. (2015) already suggested that the presence of P. indica may represent a complex of species at least in Australia (Western Australia, Queensland, New South Wales and Victoria), but also it may be the same case in other disjunct localities.On the other hand, several authors have reported P. indica through the decades, providing brief diagnoses/descriptions and illustrations that allow comparison with the re-description provided here (Table 1).The characters listed in Table 1 show great variability amongst all these records, demanding a detailed examination of voucher specimens.In addition, a study of ontogenetic variability is desirable, with special emphasis on the analysis of the following features that might be informative and consequently used in the recognition of species in Parasphaerosyllis: Some specimens with a male stolon, with proventricle as long as 3 segments (in segments 7-9, 9-11 or 12-14, respectively).

Taxon discussion
Regarding the generic features of Parasphaerosyllis, the genus was established by Monro (1937) as having fused palps, except at the extreme tip in the type species (P.indica); and dorsal cirri from the mid-region including two types: moniliform (articulated or annulated) and bulbous, both being alternating (one by one).In recent generic diagnoses provided to Parasphaerosyllis by San Martín et al. (2008) and San Martín and Aguado (2019), it is stated that the genus has palps fused only basally and dorsal cirri from mid-body being short, unarticled, lemon-like alternated with articulate cirri.Additionally, the holotype of P. indica here examined has palps fused only basally, contrary to the original description by Monro (1937).Regarding the term dorsal cirri being "lemon-like"; in our opinion, this is subjective because it does not reflect the shape of these structures in all of the four species currently valid in the genus.Lemonshaped can be spherical (as green lemon or lime) or ovoid (as yellow lemon) or pyriform and corrugated (as other lemon varieties).For instance, the dorsal cirri, originally described and illustrated by Monro (1937) (text fig.8b), are bulbous with a terminal knob, which agree with the re-examination of the holotype (this study, Fig. 1B-E).In P. malimalii, dorsal cirri from the mid-region are ovoid or bulbous with a terminal knob (Capa et al. 2001, figs. 1B and D; this study, Fig. 6A), in P. ezoensis, these cirri are bulbous with knobs composed of two terminal articles (Imajima and Hartman 1964, plate 28, fig.b), in P. uschakovi, the cirri are bulbous with knobs composed of 2-3 terminal articles (Chlebovitsch 1959, fig.1b and r) and, in the new species described below (P.irregulata sp.nov.), these cirri are spherical to bulbous and knobs have 1-3 terminal articles (Fig. 2B-C and Fig. 4C-E).Besides, the report of "P.indica" in Western Australia and Tasman Sea by San Martín et al. ( 2008) described the cirri as lemon-shaped, but it seem more like bulbous in the sense of this contribution.
Moreover, there is variation in the holotype of Parasphaerosyllis indica here examined versus the description by Monro (1937) (p.274).He described the body as "slender and thread-like", but we find that it is sub-cylindrical, widened in the first 15-16 segments to the posterior part of proventricle.The holotype is posteriorly incomplete, most of the stolon described by Monro having disappeared, perhaps due to overhandling of the specimen since other damage can be observed, such as the loss of the median and right lateral antennae.
According to the image provided by Monro (1937): fig.8a, the insertion of the lateral antennae is located between the superior and the inferior pair of eyes, but in the holotype, lateral antennae are inserted on the distal margin of prostomium and the only visible antenna (left one) is incomplete, having only seven articles.The number of articles in the dorsal tentacular cirri varies; Monro illustrates tentacular cirri in his figure 8a with 20 articles on the left side and 21 on the right; but, the dorsal tentacular cirri in the holotype have 24 articles on both sides.Finally, Monro's figure 8b shows the bulbous cirri attached to the parapodium by a prominent cirrophore.When observing the holotype, we saw that parapodia do not have cirrophores and some cirri show different degrees of basal thinning (Fig. 1C-D).

Description
Holotype complete, 35 mm long, 0.9 mm wide, 310 chaetigers.Body pale yellowish, without colour pattern, subcylindrical, ventrally flattened.Prostomium oval, wider than long.Two pairs of eyes in trapezoidal arrangement.Eyes of anterior pair longer than inferior pair, closer to external border of prostomium.Eyespots absent (Fig. 2A).Three annulate antennae.Median one with 26 articles, located in middle prostomium, between posterior eyes.Lateral antennae inserted in the anterior border of prostomium, with 16 articles each.All antennae longer than prostomium and palps.Palps subtriangular, slightly shorter than prostomium, free at their base (Fig. 2A).Peristomium as long as first chaetiger (Fig. 2A, Fig. 4A-B), with two pairs of tentacular cirri, dorsal ones with 24-25 moniliform articles, ventral ones with 13 articles each (Fig. 2A, Fig. 4A-B).Buccal hole with two large lateral edges and a central fissure formed by three irregular pleats.Dorsal cirri long, articulated.Articles near to cirrophore subrectangular, wider than long, following ones moniliform; distal article and, on occasions, subdistal ones longer than wide.First pair of dorsal cirri long, with 18 articles each.Cirri from second to sixth parapodia with 16-18 articles.After proventricle end, dorsal cirri alternating one by one (short and long), with 14-18 and 20-22 articles, respectively.In chaetiger 44 appear the first bulbous dorsal cirrus on right side only, with moniliform cirri on left side.From that region to the end of body, articulated cirri with 12-22 articles, with the exception of the last segments where it is growing and has few articles.Nearly spherical dorsal cirri in certain segments (Fig. 4C and E), while, in others, they are bulbous with distal part lengthened (Fig. 2B and Fig. 4D).The presence of spherical/bulbous cirri is irregular, not alternating one by one with moniliform cirri in all segments, but a series of up to 10 bulbous cirri can be present or 3 moniliform cirri in a row, although, sometimes, bulbous and moniliform cirri appear in the same segment forming asymmetric segments (Fig. 5A-B).Distal end of bulbous cirri with an unarticulated knob, smooth (Fig. 4C and E), although, in some cases, three or four terminal articles are present on posterior segments (Fig. 2C and Fig. 4D).

Diagnosis
Palps free at their bases.Peristomium as long as first chaetiger.Dorsal cirri from midbody spherical to bulbous with a long distal end, alternate with long and articulated cirri in an irregular pattern (they are not alternating one by one, both kinds of dorsal cirri may appear on the same segment).Bulbous and spherical dorsal cirri mostly with an unarticulated knob, but those from posterior segments can have two to four distal articles.Bidentate falcigers with short, subtriangular blade, proximal tooth slightly larger than distal one.

Etymology
The specific name refers to the irregular presence of bulbous and moniliform dorsal cirri.

Distribution
Only known from the type locality.

Ecology
The specimens were captured among biofoulers such as coralline algae, bryozoans, hydrozoans and tubes of polychaetes Spirobranchus spp., attached to pyramidal cement structures commonly used to fix coral Pocillopora spp.fragments.

Taxon discussion
Parasphaerosyllis irregulata sp.nov., differs from other species in the genus by having palps free at their base (P.ezoensis, P. indica, P. malimalii and P. uschakovi have palps fused basally) and the presence of an irregular alternation of bulbous and articulated dorsal cirri as follows: spherical to bulbous cirri with 1-3 terminal articulated knobs and moniliform ones, both distributed irregularly, sometimes a spherical/bulbous and moniliform cirrus may appear together within the same segment or only a spherical/ bulbous cirrus may appear in several consecutive segments (not alternating one by one as occurs in the other species of the genus).Besides, its is important to emphasise the lost of bilateral symmetry of dorsal cirri in some segments: shape of dorsal cirrus from the right side of a particular segment is not always replicated in the left side as occurs in other species.Furthermore, the size and shape of falciger blades (short and subtriangular) with subequal teeth (proximal tooth slightly larger than the terminal one) is a unique feature (all other four species have falcigers with longer blades than in P. irregulata sp.nov.and proximal tooth being shorter than the terminal one).
The spherical or bulbous dorsal cirri of P. irregulata sp.nov.presumably have glands over its dorsal surface, aligned in several straight rows (Fig. 4E-F), some empty pores are visible, whereas other pores show short filaments or cilia arising from the holes.Their function is unknown, as well as their presence in P. ezoensis and P.

Description
The three specimens studied are incomplete posteriorly, the largest being 9.2 mm long and 0.60 mm wide.Body subcylindrical, flattened ventrally, pale yellowish, without pigmentation pattern, with 82 chaetigers.Prostomium oval, wider than long.Four eyes in a trapezoidal arrangement, the anterior pair larger than posterior one.Three articulated antennae, the middle one with approximately 50 articles, inserted in the posterior part of the prostomium between the basal pair of small eyes.Lateral antennae with 21 articles, inserted very close to the anterior edge of the prostomium.Palps short, sub-triangular, directed slightly towards ventral side, equal to or slightly smaller than the prostomium length, fused basally.No nuchal organs are observed.Peristomium slightly shorter than the first chaetiger, covering a small area of the prostomium.Two pairs of articulated tentacular cirri, the dorsal ones with some 40 articles and the ventral ones with 20.Dorsal cirri of the first chaetiger with 45-50 articles, chaetiger 2 (20-21 articles), chaetiger 3 (28-33 articles), chaetiger 4 (30-31 articles), chaetiger 5 (20-21 articles) and chaetiger 6 (37-39 articles).Alternating long and short anterior dorsal cirri with 38-40 and 23-25 articles, respectively.First bulbous cirrus appears at chaetiger 29, regularly alternating one by one with moniliform cirri (Fig. 6A).Elongated bulbous cirri with a smooth, non-articulated terminal knob.In the smallest specimen, the first bulbous dorsal cirrus appears on chaetiger 21.Moniliform dorsal cirri of the median region of the body with 20-22 articles.Parapodial lobe subconical, truncated, with two ligules, one anterior and one posterior.Ventral cirrus subtriangular, inserted at the base, approximately half the length of the parapodial lobe.
Anterior parapodia with 9-10 bidentate falcigers per bundle (Fig. 6B).Falcigers with dorso-ventral gradation approximately 2:1.With 5-6 chaetae per fascicle on middle parapodia.One or two pseudosimple chaetae formed by the thickening of the handle and loss of the blade in the dorsal position.Four to five bidentate falcigers with shorter and thicker blades than those of anterior parapodia (Fig. 6C).Posteriorly, the number of pseudosimple chaetae increases (3-4) (Fig. 6D) and that of falcigers decreases (1-2).With three aciculae on anterior segments, one of them with a straight tip and the other two with a slightly bent tip.Mid-body parapodia with two aciculae, both with the tip slightly bent and remaining so until the end of the incomplete specimen.Pharynx through 7-8 segments, with anterior medio-dorsal tooth.Approximately the same length as the proventricle, the latter being 32 muscle cell rings.

Diagnosis
Palps fused basally.Peristomium slightly shorter than the first chaetiger, covering a small area of the prostomium.Dorsal cirri from mid-body bulbous with a long distal end, alternating with long and articulate cirri in an irregular pattern (alternated one by one).
Falcigerous bidentate with the secondary tooth very small, with pseudosimple setae formed by the thickening of the handle and the loss of the joint in the middle and posterior chaetigers.Pharynx and proventricle nearly the same size.

Distribution
Eastern Tropical Pacific, from Nayarit and Jalisco (Mexico) to Panama.

Ecology
Intertidal, associated with mats of coralline algae fixed to rocks at 2 m depth.

Biology
One of the specimens has a female dicerous stolon in poor condition of which the characteristic features cannot be seen.

Taxon discussion
This constitutes the first record of Parasphaerosyllis malimalii since its establishment.It is now reported from Nayarit and Jalisco (Central Mexican Pacific).Parasphaerosyllis malimalii is the only species within the genus to have pseudosimple chaetae formed by the thickening of the handle and loss of the blade.The specimens studied here have some differences from those originally reported to the Pacific of Panama.The median antenna is larger than original description (approx.50 articles), the alternating anterior dorsal cirri are also larger than those reported by Capa et al. (2001) (with 38-40 and short with 23-25 articles) and the number of chaetae per bundle in anterior chaetigers is also larger (9-10) than the holotype.These differences are probably due to ontogeny.

Identification keys
Taxonomic key to species of Parasphaerosyllis Monro, 1937za

Figure 4 .
Figure 4. Scanning electronic micrographs of Parasphaerosyllis irregulata sp.nov.(paratype UANL 8160).A Anterior end, dorsal view, arrows point to insertion scars of dorsal cirri; B Prostomium and first anterior segments, dorsal view; C Alternated bulbous and moniliform dorsal cirri from mid-body region; D Posterior segments showing different development stages of bulbous dorsal cirri; E Bulbous dorsal cirrus showing dorsal band of several lines of pores; F Detail of ciliate pores on bulbous dorsal cirrus.Scale bars: A, B = 0.5 mm; C, D = 50 µm; F = 5 µm.

Figure 5 .
Figure 5. Scanning electronic micrographs micrographs of Parasphaerosyllis irregulata sp.nov.(paratype UANL 8160).A Middle section of the body, dorsal view, square showing an enlargement of a spherical cirrus with two terminal articles; B Posterior section of the body, dorsal view, where "b" means bulbous cirrus and "m" moliniform cirrus; C Terminal end, lateral view; D Anterior parapodium with falcigers; E Falcigers from middle body; F Falcigers from posterior parapodia.Scale bars: A, B = 0.5 mm; C = 0.1 mm; D, F = 10 µm, E = 5 µm.

Table 1 .
Reports of Parasphaerosyllis indicaMonro, 1937around the globe presented in chronological order.Only records that include diagnosis, drawings or some information were here considered.Antennae longer than those described by San Martín et al. (2008)", it could be interpreted as having more than 24 articles; anal papilla inflated, similar to spherical dorsal cirri (it suggesting that dorsal cirri are spherical).
first pair of dorsal cirri with 60 articles; bulbous dorsal cirri starting at chaetiger 26, with a terminal knob; alternation one by one; proventricle with 20 rows of muscle cells.Cantone 1976: 230 SomaliaProventricle as long as 5 segments; bulbous cirri appear at chaetiger 16; bulbous cirri with terminal articles.

Parasphaerosyllis malimalii Capa, San Martín & López, 2001 Nomenclature Parasphaerosyllis
Capa et al. (2001)8)e record of SanMartín et al. (2008): figs.19E-F,SEM, as "P.indica" from the Tasman Sea (specimen AM W30153), some pores are visible on the surface of bulbous dorsal cirri, but in the figure, it cannot be seen if the pores are aligned in rows as in P. irregulata or in a scattered pattern.Besides, the specimens from Tasman Sea and Western Australia reported by SanMartín et al. (2008): fig.22A, have bulbous dorsal cirri with dark, fibrillar inclusions forming nearly diagonal lines, as well as those illustrated byCapa et al. (2001): fig.1DtoP.malimalliand those here described in the holotype of P. indica.It is unknown if that pattern is distinctive of these three taxa or not or if these are related to pores or glands.malimaliiCapa,SanMartín and López, 2001: 281, figs.1-2.Re-description of Parasphaerosyllis indica Monro, 1937 (Annelida, Syllidae), ...