A new species of Paracomesoma (Comesomatidae) from Maldives (Indian Ocean) with an emended diagnosis and an updated key of the genus

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1 Journal of the Marine Biological Association of the United Kingdom, 2015, 95(2), # Marine Biological Association of the United Kingdom, 2014 doi: /s A new species of Paracomesoma (Comesomatidae) from Maldives (Indian Ocean) with an emended diagnosis and an updated key of the genus federica semprucci Dipartimento di Scienze della Terra, della Vita e dell Ambiente (DiSTeVA), Università di Urbino, loc. Crocicchia, Urbino, Italy A new species from the subfamily Comesomatinae is described from the back-reef platforms of the central part of the Maldivian archipelago. Paracomesoma susannae sp. nov. is characterized by a large-sized body, very long cephalic sensilla (72 91 mm long), lateral differentiation of punctuations, and, in the males, minute precloacal supplements, relatively short spicules ( anal body diameter) and a hook-like structure in the distal end of the gubernaculum. Paracomesoma susannae sp. nov. is the only species so far described of the genus which appears to have such a low ratio of the outer labial and cephalic sensilla (about 0.02). An emended diagnosis of P. paralongispiculum is proposed, along with an updated and modified key to all the valid species of the genus Paracomesoma. Keywords: Comesomatinae, Paracomesoma, identification key, back-reef platforms, coral sediments, Maldives Submitted 2 February 2014; accepted 12 July 2014; first published online 4 September 2014 INTRODUCTION The family Comesomatidae is represented by more than 150 species (Fonseca & Bezerra, 2014). It is documented worldwide and is among the most common and abundant components of muddy or silty sediments (Heip et al., 1985). The phylogenetic position of Comesomatidae has long been debated (see Fonseca & Bezerra, 2014 for details). However, current molecular data support the family Comesomatidae as a member of the order Monhysterida (Meldal et al., 2007). Comesomatidae are currently divided into three subfamilies: Comesomatinae, Dorylaimopsinae and Sabatieriinae. Comesomatinae are characterized by elongate spicules and buccal cavities cylindrical, dilated or collapsed, provided with projections at the border to the anterior portion. Dorylaimopsinae are characterized by the posterior part of the buccal cavity structurally expanded, with tooth-like structures present, while Sabatieriinae are characterized by the lack of these two features (Platt, 1985). The Comesomatinae sub-family consists of four genera: Comesoma, Paracomesoma, Metacomesoma and Comesomoides, for a total of 28 species. The Paracomesoma genus is the most species-rich genus of Comesomatinae, comprising itself 14 species (Tu et al., 2013). The genus Paracomesoma was established by Stekhoven (1950) for systematizing the new species Paracomesoma coronata. He also transferred Comesoma dubium Filipjev, 1918 to the genus Corresponding author: F. Semprucci federica.semprucci@uniurb.it Paracomesoma because of the structure of the buccal cavity. Subsequently, Wieser (1954) synonimized P. coronata with Paracomesoma dubium. The genus Paracomesoma was considered invalid by Hopper (1967), because no type species had been designated. However, Hopper reinstated the genus in order to accommodate two species of the genus Laimella: Laimella hexasetosa Chitwood, 1937 and L. quadrisetosa Chitwood, 1937, since the characteristic structure of their male apparatus did not fit that of the genus Laimella. Hopper also moved Vasostoma longispiculum Timm, 1961 in the Paracomesoma genus for the small buccal cavity, the presence of elongated spicules and the absence of caudally directed apophyses on gubernaculum. Later, Hope & Murphy (1972) designated Comesoma dubium (Filipjev, 1918) as the type species of the genus Paracomesoma. Jensen & Gerlach (1977) described P. inaequale and assigned Comesa sipho Gerlach, 1956 to this genus, on the basis of the structure of the buccal cavity and the copulatory apparatus. For the same reason Jensen (1979) also transferred Sabatieria curvispiculum Allgén, 1959 to the genus. The last species included in the genus were: P. curvatum Gagarin & Thanh, 2006; P. elegans Gagarin & Thanh, 2009; P. heterosetosum Zhang, 1991; P. lissum Gagarin & Thanh, 2009; P. paralongispiculum Tu et al., 2013; P. sigmoidalis Riera et al., 2006; and P. xiamenense Zou, In samples recently collected from back-reef platforms of the Maldivian archipelago, some specimens belonging to the Paracomesoma genus were found. In this type of habitat, Comesomatidae represented less than 1% of the total community (Semprucci et al., 2010, 2011), but their importance appeared to increase in coral sediments of the deeper subtidal habitats in relation to the greater mud fraction (Semprucci 339

2 340 federica semprucci b: total body length divided by pharyngeal length c: total body length divided by tail length cbd: corresponding body diameter hd: head diameter L: body length Mbd: maximum body diameter s : spicule length divided by abd spic: spicule PL: pharynx length TL: tail length. RESULTS Fig. 1. Map of the Maldivian archipelago showing the type localities. et al., 2013, 2014). No Comesomatidae species had been documented so far for the Maldivian archipelago. Here, a new species of Paracomesoma is described and its systematic position is discussed. This is also an occasion to emend the diagnosis of a species of the genus recently described and to propose a modified, updated identification key to the species of Paracomesoma. MATERIALS AND METHODS Samples of sediment were collected from the atolls of South Malé and North Felidu in May 2005 and 2007 (Figure 1). The studied habitats were back-reefs platforms entirely characterized by coral sediments (Semprucci et al., 2010, 2011). The samples were collected by a diver using a Plexiglass corer tube (diameter 2 cm) which was pushed 5 cm into the sediment. The sediment was immediately treated with 7% MgCl 2 to relax the fauna, fixed with a 4% formaldehyde solution (in buffered seawater), meiofauna were obtained by sieving the samples through a 42 mm mesh net and animal extraction was performed by flotation and multiple decantation. When a high amount of fine fraction was present, samples were centrifuged using a silica gel gradient (Ludox HS 30, density 1.18 g cm 23 ) (Pfannkuche & Thiel, 1988). Nematode specimens were isolated under a stereomicroscope, transferred in glycerine and mounted as permanent slides (Seinhorst, 1959). The specimens were identified under a 100 oil immersion objective with DIC Nomarski illumination (Optiphot-2 Nikon). Drawings were made using a camera lucida mounted on a Zeiss Universal microscope. All measurements are in micrometres and curved structures were measured along the arc. Abbreviations a: total body length divided by maximum body diameter abd: anal body diameter systematics Order MONHYSTERIDA Filipjev, 1929 Superfamily AXONOLAIMOIDEA Filipjev, 1918 sensu Chitwood & Chitwood, 1950 Family COMESOMATIDAE Filipjev, 1918 Subfamily COMESOMATINAE Filipjev, 1918 Genus Paracomesoma Hope & Murphy, 1972 Genus Paracomesoma Hope & Murphy, 1972 (emended from Jensen, 1979; Platt, 1985) diagnosis Cuticle with transverse annules or puntuactions, sometimes difficult to discern. Lateral differentiation present or absent. Anterior sensilla in three distinctly separated crowns. Posterior portion of the buccal cavity cylindrical, with strongly sclerotized walls and provided with three or six thorn-like projections at the border of the anterior portion. Spicules long and slender. Gubernaculum plate-like without dorsal apophysis. Number of species: 14 type species P. dubium (Filipjev, 1918). list of valid species The present list of valid species is accord with Tu et al. (2013). For each species taxonomic notes and geographical distribution are specified. Paracomesoma curvispiculum (Allgén, 1959); Allgén, 1959: 154, fig. 155a, b [Sabatieria curvispiculum]; Jensen, 1979: 93 (Paracomesoma curvispiculum comb. nov.); South Georgia. Paracomesoma curvatum (Gagarin & Thanh, 2006); Gagarin & Thanh, 2006: , figures 16 22; Tu et al., 2013: 146 (erroneously reported as P. curvitatus); Vietnam. Paracomesoma dubium (Filipjev, 1918); Filipjev, 1918: , figure 77a c [Comesoma dubium]; Kreis, 1929: 82 83, figure 36a f (Comesoma dubia); Stekhoven, 1950: , figure 89a f (syn. Paracomesoma coronata) op Wieser (1954): 140; Gerlach, 1964: 20 (Laimella dubia); Zhou & Zhang, 2003: , figure 3; Black Sea, English Channel, Mediterranean Sea, Red Sea, Hong Kong. Paracomesoma elegans (Gagarin & Thanh, 2009); Gagarin & Thanh, 2009: 7 10, figure 1; Vietnam. Paracomesoma heterosetosum Zhang, 1991; Zhang, 1991: 54 56, figures 5 10; Bohai Sea.

3 paracomesoma susannae from maldivian archipelago 341 Fig. 2. Paracomesoma susannae sp. nov.: (A) detail of the cephalic region of a male paratype; (B) pharyngeal region of the holotype; (C) pharyngeal region of the allotype; (D) female paratype habitus; (E) tail view of holotype; (F) holotype habitus. Scale bars: A, 10 mm; B, C, 50 mm; D, F, 200 mm; E, 40 mm. Paracomesoma hexasetosum (Chitwood, 1937); Chitwood, 1937: 59, figure 21f h [Laimella hexasetosa]; Hopper, 1967: 140 (Paracomesoma hexasetosum comb. nov.); Pearse et al., 1942: 182; North Carolina. Paracomesoma inaequale (Jensen & Gerlach, 1977); Jensen & Gerlach, 1977: 61 63, figures 1, 2; Bermuda. Paracomesoma lissum (Gagarin & Thanh, 2009); Gagarin & Thanh, 2009: 10 11, figure 2; Vietnam. Paracomesoma longispiculum (Timm, 1961); Timm, 1961: 53 54, figure 38a c [Vasostoma longispiculum]; Hopper, 1967: 140 (Paracomesoma longispiculum comb. nov.); Bay of Bengal. Paracomesoma quadrisetosum (Chitwood, 1937); Chitwood, 1937: 58 59, figure21d, e[laimella quadrisetosum]; Chitwood & Chitwood, 1937 (1938): figure 60y; Pearse et al., 1942: 182; Wieser, 1960:126;Hopper,1967:140(Paracomesoma quadrisetosa comb.nov.);northcarolina,massachusetts,usa. Paracomesoma paralongispiculum (Tu et al., 2013); Tu et al., 2013: , figures 1, 2; Vietnam. Paracomesoma sigmoidalis (Riera et al., 2006); Riera et al., 2006: 55 58, figures 1, 2, Canary Islands, North Atlantic Ocean. Paracomesoma sipho (Gerlach, 1956); Gerlach, 1956: , figure 27c e [Comesoma sipho]; Jensen & Gerlach, 1977: 62(Paracomesoma sipho comb. nov.); Tu et al., 2013: 146 (erroneously reported as P. siphon); Pernambuco, Brazil. Paracomesoma xiamenense (Zou, 2001); Zou, 2001: 50 52, figures 1, 9 13; Tu et al., 2013: 146 (erroneously reported as P. xiamenese); Xiamen Islands, China (Figures 2, 3 and Table 1). Paracomesoma susannae sp. nov.

4 342 federica semprucci Fig. 3. Paracomesoma susannae sp. nov.: (A) lateral view of amphid; (B) buccal cavity of holotype; (C) lateral differentiation in the pharyngeal region; (D) detail of the hook-like structure in the distal part of the gubernaculum; (E) detail of the precloacal supplements; (F) ejaculatory glands in the precloacal region of the holotype; (G) detail of the spinneret in the holotype; (H) mid-body region showing vulva of a paratype female. Scale bars: A E, G, H, 10 mm; F, 50 mm. specimens Four males; five females; three juveniles. type material The holotype, allotype and paratypes (3F and 4C) are deposited at the Department of Earth, Life and Environmental Sciences (DiSTeVA), University of Urbino, Italy. The material was collected by Maria Balsamo, Paolo Colantoni and Giuseppe Baldelli. type locality The new species has been found in back-reef platforms characterized by coral sediments (Maldive Islands, Indian Ocean).

5 paracomesoma susannae from maldivian archipelago 343 Table 1. Morphometric measurements for Paracomesoma susannae sp. nov. (all measurements in mm, except ratios values; for paratypes minimum and maximum values are provided). Holotype Male paratypes (N 5 3) (minimum maximum) Allotype Female paratypes (N 5 4) (minimum maximum) Juveniles (N 5 3) (minimum maximum) Total length 3915 ( ) 3570 ( ) ( ) Head diameter 18 (19 20) 18 (18 19) (13 15) Inner labial sensilla 1 (1 2) 1 (1 2) 1 Outer labial sensilla 2 (2) 2 (1 2) n/v Cephalic sensilla 70 (72 91) 74 (74 91) (40 51) Subcephalic setae 34 (22 37) 34 (34 42) (16 21) Cervical setae 26 (25 28) 28 (25 29) Distance from anterior to anterior edge of amphid 8 (9) 8 (8 10) (6 10) Amphid turns 2.5 ( ) 2 (2 2.5) (2.25) Amphid diameter 14 (13 15) 13 (11 14) (8 10) Amphid cbd 23 (24 24) 21 (21 24) ( ) Distance from anterior edge to nerve ring 126 (122) 124 ( ) n/v Nerve ring cbd 43 (46) 43 (37 45) Distance from anterior edge to excretory pore 149 ( ) 142 ( ) ( ) Pharynx Lenght 233 ( ) 224 ( ) ( ) Pharynx cbd 49 (51 53) 48 (41 54) (24 28) Maximum body diameter 55 (60 64) 53 (52 60) (25 33) Distance from anterior edge to vulva 1844 ( ) cbd at vulva 53 (52 60) Length of anterior ovary, measured from vulva 484 ( ) Length of posterior ovary, measured from vulva 477 ( ) Spicules 119 ( ) Distance from anterior to anus 3678 ( ) 3319 ( ) ( ) Anal body diameters (abd) 41 (43 53) 37 (36 50) (20 25) Gubernaculum 47 (43 45) Number of supplements 20 (19 22) Distance from anus to most posterior supplement 10 (9) Distance from anus to most anterior supplement 352 ( ) Tail length (TL) 275 ( ) 251 ( ) ( ) Number of terminal setae 1 (1) Length of terminal setae 11 (10 13) a 71.7 ( ) 66.9 ( ) ( ) b 16.8 ( ) 16.0 ( ) ( ) c 14.2 ( ) 14.2 ( ) ( ) s 2.9 ( ) The holotype was found in Gulhi Island (South Malé Atoll) at 0.60 m (Figure 1). additional localities Male paratypes were found in Kudadhiggaru Falhu (Felidu Atoll) and Gulhi Island from 0.60 to 1.10 m (Figure 1). Female paratypes were found in Gulhi Island, Kudadhiggaru Falhu from 0.30 to 1.10 m. Juveniles were found in the same localities at a depth of 1.10 m. type habitat The holotype was collected by poorly sorted medium sands at a depth of 0.60 m. The sediments were composed of 7.6% of gravel, 90% of sand and 2.6% of clay with a sorting of Overall, the new species has been recorded at depths between 0.30 and 1.10 m. The coral sediments were characterized from poorly sorted medium to very coarse sands (gravel: %, sand: 81 90%, clay: %). etymology The species is named in honour of Professor Susanna De Zio-Grimaldi (University of Bari, Italy), in recognition of her contribution to the field of marine meiobenthology. description Male Body slender with a conical cylindrical tail. Small and regular punctuations at ventral and dorsal body sides. Lateral body fields with large dots in few transversal rows and irregularly arranged from the first third of the pharynx. Size of larger dots increasing gradually up to the end of the pharynx. Buccal cavity small, armed at the base with three teeth. Multispiral amphideal fovea with 2.5 turns, located closely behind the sub-cephalic setae. Anterior border of fovea at 7.8 mm from anterior body end. Diameter of amphidial fovea 0.6 of the c.b.d.. Inner and outer labial sensilla in form of setiform papillae. Cephalic sensilla very long (3.88 hd long) located 0.52 hd from the anterior body end. Sub-cephalic setae (1.90 hd long) very close to cephalic sensilla, at 0.66 hd from anterior extremity. A ring of cervical setae (26 mm long) immediately behind the amphid. Somatic setae (about 0.28 cbd long) scattered and numerous. Pharynx cylindrical that anteriorly surrounds the entire buccal cavity and posteriorly gradually enlarges into a bulb (26% of the PL). Pharynx with evident granulations for most of its length and striations in the bulb region. Nerve ring at about 54% of the PL. Secretory excretory pore just

6 344 federica semprucci Table 2. Morphometrics of males of valid species of the genus Paracomesoma. Body lenght (mm) Presence a b c s Presence and of inaequal number of precloacal outer setae supplements P. curvispiculum (Allgén, 1959) Jensen, NO YES, but number na P. curvatum Gagarin & Thanh, NO P. dubium (Filipjev, 1918) Stekhoven, 1950 a NO P. elegans Gagarin & Thanh, NO P. heterosetosum Zhang, YES P. hexasetosum (Chitwood, 1937) Hopper, YES P. inaequale Jensen & Gerlach, YES P. lissum Gagarin & Thanh, NO P. longispiculum (Timm, 1961) Hopper, NO or more P. paralongispiculum Tu et al., NO b P. quadrisetosum (Chitwood, 1937) Hopper, NO or more P. susannae sp. nov NO P. sigmoidalis Riera et al., NO P. sipho (Gerlach, 1956) Jensen & Gerlach, YES P. xiamenense Zou, NO in 2 lines na, not available; a, the measurements of the original description have been integrated with Zhou & Zhang (2003); b, the ratio is refered to the new measurements taken by the author. anterior to pharyngeal bulb (64% of PL) with a prominent excretory cell just posterior to the bulb. Cardia cells not visible. Reproductive system diorchic. Testes opposite and outstretched with visible spermatozoa irregularly oviform. Male spicules paired and elongate (118.5 mm, 2.9 abd) with a cephalate capitulum. Tubular gubernaculum covering almost one-third of the spicule length (46.6 mm). Presence of a hook-like structure in the distal part of the gubernaculum. Numerous ejaculatory lateral glands situated anteriorly to cloaca, 8 left, 10 right. Minute pre-cloacal supplements (20 in the holotype and in the paratypes). Caudal glands not observed. Tail is conical cylindrical, 275 mm long, without an evident spinneret; a single terminal seta, 11.1 mm long. Female General appearance similar to the male s one. Cuticle with irregular punctations and lateral differentiation. Buccal cavity small, armed at the base with three teeth. Multispiral amphideal fovea with two turns (diameter 0.6 cbd) close behind sub-cephalic setae (8 mm from anterior body end). Inner and outer labial sensilla in form of setiform papillae. Cephalic sensilla very long (4 hd long) located 0.5 hd from anterior body end. Sub-cephalic setae (2 hd long) very close the cephalic setae, located on 0.7 hd from anterior extremity. A ring of cervical setae 28 mm long. Somatic setae numerous and 0.2 cbd long. Pharynx gradually enlarging posteriorly into a bulb (25% of the PL). Nerve ring at 55% PL from anterior, while the secretory excretory pore at 63% of PL. Genital system didelphic, amphidelphic with outstretched ovaries (anterior branch: 484 mm; posterior branch: 477 mm). Eggs observed in the uterus with a spermatheca for each branch containing oval sperm cells. Vulva located at 52% of the body length. Vagina surrounded by constrictor muscles, granular vaginal glands present. Tail 251 mm long, no terminal setae observed. Juveniles Similar to adults in most morphological aspects. diagnosis Paracomesoma susannae sp. nov. is characterized by a comparatively slender and large-sized body (L ¼ mm, a ¼ 59 71), very long cephalic setae (72 91 mm long), lateral differentiation of punctuations, and in the males minute precloacal supplements, relatively short spicules ( mm corresponding to abd) and a hook-like structure in the distal part of the gubernaculum. Furthermore, P. susannae sp. nov. is unique within this genus, for the especially low ratio between the length of the outer labial and the cephalic sensilla, respectively (about 0.02). differential diagnosis Paracomesoma susannae sp. nov. is especially similar to P. dubium, P. quadrisetosum, P. hexasetosum and P. lissum for the low s value. However, the new species differs in the largest de Man s ratios a and b, the presence of a lateral differentiation of the cuticle and the more anterior location of the sub-cephalic setae. The latter character was also described in P. sigmoidalis in which, however, they are 28 mm vs 12 mm far from the anterior end. Furthermore, P. susannae sp. nov. has a larger de Man s ratio (a, b, c) and a shorter spicule ( vs ). In addition, the number of precloacal supplements is lower with respect to all the above cited species (19 22 in P. susannae sp. nov. vs more than 40 in P. hexasetosum, in P. lissum, more than 30 in P. quadrisetosum, 35 in P. sigmoidalis) (Table 2). remarks Tu et al. (2013) stated that P. curvatum and P. longispiculum are the closest species to P. paralongispiculum, and reported the notable length of the spicule apparatus as the main distinctive character of the latter species. Re-examination of the holotype and paratypes of P. paralongispiculum revealed a shorter spicule length compared to that reported in the original description: 9.8 abd and 310 mm of length in the holotype ( mm corresponding to abd in the paratypes). In particular, the comparison of

7 paracomesoma susannae from maldivian archipelago 345 this species with P. curvatum clearly shows that there is no sharp distinction between the respective ranges of the s ratio ( vs abd). However, the two species also differ in the number and distribution of the papillae supplements: restricted to the spicular region in P. paralongispiculum vs (5 8 supplements in the spicular region) in P. curvatum. Furthermore, only the latter species has two distal sclerotized drop-shaped pieces of the gubernaculum. Paracomesoma longispiculum differs from P. paralongispiculum in having longer cephalic setae (8 mm vs 5 mm), shorter spicules (only 225 mm long) and more precloacal supplements (50 cuticular bumps. According to these new observations the diagnosis of P. paralongispiculum is emended as follows. According to these new observations the diagnosis of P. paralongispiculum is emended as follows. Paracomesoma paralongispiculum Tu et al., 2013 Diagnosis (emended from Tu et al., 2013) Male Body 1.8 mm long. Cuticular ornamentation characterized by punctuations at ventral and dorsal sides of the body. Lateral differentiations consisting of larger dots rather than punctuations. Width of lateral fields about 30 35% of the cbd. Labial region with six inner labial papillae; six outer short labial setae 4 mm long. Four slender cephalic setae, 5 mm long (50% of the cbd). Four cervical setae, 6 mm long, at 25 mm fromanterior body end. Somatic setae, 6 mm long, arranged into regularly scattered, sublateral rows. Multispiral amphideal fovea with 2.5 turns, situated at the cephalic setae region (diameter 79%). Buccal cavity composed of two parts, the anterior cupshaped, with three small teeth, the posterior in form of a cuticularized tube 1.5 times as long as the labial region width. Pharynx gradually enlarging towards the posterior end, 179 mm long. Nerve ring at 102 mm fromtheanterior end (57% of the PL). Secretory excretory system consisting of unicellular gland located at anterior intestine; duct with distinct ampulla and pore at 110 mm from anterior end. Reproductive system diorchic, testes opposite and outstretched. Male spicules 310 mm long, thin and bent (9.8 abd); proximal part open, weakly developed. Gubernaculum small, 5 mm long. Precloacal ventromedian supplements, 11 in number; small, indistinct papillae in the spicular region. Tail short (157 mm long), with conical anterior portion and narrow cylindrical posterior portion. Caudal setae short and numerous. Tail tip with three terminal setae 7 mm long. Caudal glands present within the tail region; spinneret short, conical. Female Similar to the male in general morphology. Body 1.9 mm long. Cuticle striated and marked by fine irregular punctuations, larger at lateral body sides than at ventral and dorsal ones. Somatic setae short, 6 mm long, and numerous. Cephalic end set off from the rest of body by a slight narrowing. Internal labial papillae small. Outer labial setae 4 mm long, and four cephalic setae, 5 mm long. Multispiral amphideal fovea with 2.5 turns, situated at the posterior cephalic setae region (diameter 71 % of cbd). Pharynx swollen posteriorly, 185 mm long. Cardia small, embedded within the intestine. Length of rectum approximately equal to 1/3 of abd. Ventral gland compact, situated at cardia level; secretory excretory pore at distance 117 mm from anterior body end. Reproductive system didelphic, amphidelphic with ovaries outstretched. Uterus filled with mass of round spermatozoa. Vagina short, with muscular walls, opening into a vulva at middle body, at 44% of body length. Tail with conical anterior portion, and cylindrical posterior portion, the former 0.7 times as long as the latter. Tail provided with short caudal setae. Tail tip enlarged, with three terminal setae 6 7 mm long, spinneret short, conical. KEY OF THE GENUS PARACOMESOMA Previous keys of the genus have been proposed by Jensen (1979), Zhang (1991), Zou (2001) and finally Tu et al. (2013). With the addition of the new Maldivian species, the present list of Paracomesoma species includes 15 valid species. A modified, updated key for identification of the species of the genus is reported. 1. All the six setae of outer labial setae ring similar... 2 Lateral setae of outer labial setae ring longer than the others Spicules.7.0 times abd... 3 Spicules,7.0 times abd Spicules times abd with distal sclerotized dropshaped pieces; 5 8 supplements restricted to the spicular region... P. curvatum Spicules times abd; distal sclerotized dropshaped pieces absent; supplements restricted to the spicular region.... P. paralongispiculum 4. Spicules long 6.0 times abd;.50 supplements; male body length 1.5 mm... P. longispiculum Spicules,6.0 times abd;,50 supplements Spicules unequal in length; on average 5.8 times abd; supplements in 2 rows; male body length mm... P. xiamenense Spicules equal in length,5.8 times abd Body length,1.9 mm... 7 Body length.1.9 mm Spicules 2.0 times abd; male body length mm... P. quadrisetosum Spicules.2.0 times abd Spicules 4.6 times abd; 8 12 supplements; cuticle with laterally differentiated punctuations; male body length mm... P. elegans Spicules 3.2 times abd; supplements; cuticle smooth; male body length mm... P. lissum 9. Spicules 3.9 times abd; male body length 2.1 mm... P. curvispiculum Male body length.2.3 mm Spicules times abd; a hook-like structure in gubernaculum distal part; supplements; male body length mm... Paracomesoma susannae sp. nov. Spicule.2.9 times abd; hook-like structure in gubernaculum distal part absent Spicules times abd; 40 supplements; amphideal fovea with turns, male body length mm... P. dubium Spicules times abd; 35 supplements; amphideal fovea with 3.5 turns; male body length mm P. sigmoidalis

8 346 federica semprucci 12. Lateral outer labial setae 2 times as long as the other four cephalic setae; spicules equal or.5 times abd Lateral outer labial setae.2 times as long as other four setae Spicules 5 times abd; male body length 2.3 mm... P. sipho Spicules times abd; paired cervical setae just posterior to the amphideal fovea; gubernaculum with a small directly dorsally projection; male body length mm... P. heterosetosum 14. Lateral setae of outer labial sensilla 5 times as long as other four setae; spicules 2 times abd;.40 supplements; male body length 2.2 mm... P. hexasetosum Lateral setae of outer labial sensilla 4 times as long as four setae; 6 sclerotized, double-hooked projections in anterior buccal cavity; spicules times abd; supplements; male body length mm... P. inaequale DISCUSSION The key characters most useful in differentiating the species of this genus are the body size, relative lengths of the outer labial setae, the relative size of the male spicules and the number and arrangement of the precloacal supplements. Although the differences in the number of supplements may be important to distinguish species in this genus and in other genera of the Comesomatidae family, they are often minute and difficult to observe. Accordingly, Barnes et al. (2012) suggested the use of a scanning electrom microscope (SEM) to determine the exact number of supplements in some representatives of this family. However, the opening of these supplements is so minute that sometimes is difficult to detect even by SEM (personal observations) and thus their use as one of the main characters for a diagnostic key becomes problematic. This issue and the problems concerned with the spicule length of P. paralongispiculum, highlight the need to increase the number of characters usable for the identification key of the genus. Additional informative characters may be the number of turns and relative diameters of the amphid, the number and shape of teeth, and the shape and relative size of the gubernaculum. The cuticle arrangement is very variable from unornamented to striated cuticle or with transverse punctuation. Also lateral differentiation may occur with larger regular or irregular punctuations. Noteworthy is that the new species of Paracomesoma has pre-cloacal ejaculatory glands. They had been previously recorded in other Comesomatidae such as Cervonema, Hopperia, Laimella (Hope & Zhang, 1995; Barnes et al., 2012), but this is the first report in a species of Paracomesoma. As also suggested by Barnes et al. (2012), it is possible that their presence is rather frequent in the family, but overlooked. ACKNOWLEDGEMENTS The author is greatly thankful to both anonymous referees who improved considerably the manuscript with their valuable comments. A special thank you is due to Professor Aldo Zullini (University of Milano-Bicocca, Italy) and Professor Maria Balsamo (University of Urbino, Italy) for their support in these years. Furthermore, I warmly thank Professor Ann Vanreusel for providing the type material deposited at the Museum of Zoology, University of Ghent, Belgium and Professor Nguyen Vu Thanh for fruitful discussion. REFERENCES Allgén C.(1959) Free-living marine nematodes. Further zoological results of the Swedish Antarctic expedition, under the direction of Dr. Otto Nordenskjold. V(2) P.A. Stockholm: Norstedt & Söner, 293 pp. Barnes N., Kim H.G. and Lee W. (2012) New species of free-living marine Sabatieriinae (Nematoda: Monhysterida: Comesomatidae) from around South Korea. Zootaxa 3368, Chitwood B.G. (1937) A new genus and ten new species of marine nematodes from North Carolina. Proceedings of the Helminthological Society of Washington 4, Chitwood B.G. and Chitwood M.B. (1950) An introduction to nematology, 2nd edition. Baltimore, MD: Monumental Printing Company, 372 pp. Filipjev I. (1918) Nématodes libres marins des environds de Sébastopol, Partie I. Trudy Osoboi Zoologicheskoi Laboratorii l Sevastopol skoi Biologicheski Stantsii, 4, 362 pp. [English translation by Raveh, M. (1968), Israel Program for Scientific Translations, Jerusalem, 255 pp.]. Filipjev I. (1929) Les Nématodes libres de l extrémité orientale du golfe de Finlande et de la baie de la Néva. Études de la Neva 5, Fonseca G. and Bezerra T.N. (2014) Order Araeolaimida De Coninck & Schuurmans Stekhoven, In Schmidt-Rhaesa A. (ed.) Handbook of zoology, Gastrotricha, Cycloneuralia and Gnathifera, Berlin: De Gruyter, pp Gagarin V.G. and Thanh N.V. (2006). Three new species of free-living nematodes of the family Comesomatidae from the delta of the Mekong River, Vietnam (Nematoda: Monhysterida). Zoosystematica Rossica 15, Gagarin V.G. and Thanh N.V. (2009) Three new species of free-living nematodes from mangrove of Mekong River, Vietnam. International Journal of Nematology 19, Gerlach S.A. (1956) Die Nematoden besiedlung des tropischen Brandungsstrandes von Pernambuco Brasilianische Meers-nematoden II. Kieler Meeresforschungen 12, Gerlach S.A. (1964) Freilebende Nematoden aus dem Roten Meer. Kieler Meeresforschungen 20, Heip C., Vincx M. and Vranken G. (1985) The ecology of marine nematodes. Oceanography and Marine Biology: an Annual Review 23, Hope W.D. and Murphy D.G. (1972) A taxonomic hierarchy and checklist of the genera and higher taxa of marine nematodes. Smithsonian Contributions to Zoology 137, Hope W.D. and Zhang Z. (1995) New nematodes from the Yellow Sea, Hopperia hexadentata n. sp. and Cervonema deltensis n. sp. (Chromadorida: Comesomatidae), with observations on morphology and systematics. Invertebrate Biology 114, Hopper B.E. (1967) Free-living marine nematodes from Biscayne Bay, Florida. I. Comesomatidae: the male of Laimella longicauda Cobb, 1920, and description of Actarjania new genus. Marine Biology 1, Jensen P. (1979) Revision of Comesomatidae (Nematoda). Zoologica Scripta 8, Jensen P. and Gerlach S.A. (1977) Three new Nematoda Comesomatidae from Bermuda. Ophelia 16,

9 paracomesoma susannae from maldivian archipelago 347 Kreis H.A. (1929) Freilebende marine Nematoden von der Nordwestküste Frankreichs (Trébeurden Côtes du Nord). Capita Zoologica 2: Meldal B.H.M., Debenham N.J., De Ley P., De Ley I.T., Vanfleteren J.R., Vierstraete A.R., Bert W., Borgonie G., Moens T., Tyler P.A., Austen M.C., Blaxter M.L., Rogers A.D. and Lambshead P.J.D. (2007) An improved molecular phylogeny of the Nematoda with special emphasis on marine taxa. Molecular Phylogenetics and Evolution 42, Pearse A.S., Humm H.J. and Wharton G.W. (1942) Ecology of sand beaches at Beaufort, North Carolina. Ecological Monographs 12, Pfannkuche O. and Thiel H. (1988) Sample processing. In Higgins R.P. and Thiel H. (eds) Introduction to the study of meiofauna. Washington, DC: Smithsonian Institution Press, pp Platt H. (1985) The free-living marine nematode genus Sabatieria (Nematoda, Comesomatidae) taxonomic revision and pictorial keys. Zoological Journal of the Linnean Society 83, Riera R., Nunez J. and Brito M.D.C. (2006) Two new species of Comesomatidae Filipjev, 1922 (Nematoda: Chromadorida) from sandy bottoms of Tenerife, Canary Islands. Zootaxa 1126, Seinhorst J.W. (1959). A rapid method for the transfer of nematodes from fixative to anhydrous glycerine. Nematologica 4, Semprucci F., Colantoni P., Baldelli G., Rocchi M. and Balsamo M. (2010) The distribution of meiofauna on back-reef sandy platforms in the Maldives (Indian Ocean). Marine Ecology: an Evolutionary Perspective 31, Semprucci F., Colantoni P., Baldelli G., Sbrocca C., Rocchi M. and Balsamo M. (2013) Meiofauna associated with coral sediments in the Maldivian subtidal habitats (Indian Ocean). Marine Biodiversity 43, Semprucci F., Colantoni P., Sbrocca C., Baldelli G. and Balsamo M. (2014). Spatial patterns of distribution of meiofaunal and nematode assemblages in the Huvadhoo lagoon (Maldives, Indian Ocean). Journal of Marine Biological Association of the United Kingdom. doi: /s x. Semprucci F., Colantoni P., Sbrocca C., Baldelli G., Rocchi M. and Balsamo M. (2011) Meiofauna in sandy back-reef platforms differently exposed to the monsoons in the Maldives (Indian Ocean). Journal of Marine Systems 87, Stekhoven J.H. (1950) The free-living marine nemas of the Mediterranean. I. The Bay of Villefranche. Mémoires de l Institut Royal des Sciences Naturelles de Belgique 2 série 37, Timm R.W. (1961) Three marine nematodes of the Bay of Bengal. Proceedings of the Pakistan Academy of Science 1, Tu N.D., Vanreusel A., Smol N., Long P.K. and Thanh N.V. (2013) Paracomesoma paralongispiculum sp. n.: a new species of nematode from mangroves of Can Gio (Vietnam) and taxonomy of the genus Paracomesoma Hope et Murphy, 1972 (Nematoda: Araeolaimida). Russian Journal of Marine Biology 39, Wieser W. (1954) Free-living marine nematodes. II. Chromadoroidea. Chile Reports 17. Lunds Universitets Årsskrift. Ny Foljd. Avdelningen 60, Wieser W. (1960) Benthic studies in Buzzards Bay. II. The meiofauna. Limnology and Oceanography 5, Zhang Z.N. (1991) Two new species of marine nematodes from the Bohai Sea, China. Journal of Ocean University of Qingdao 21, Zhou H. and Zhang Z. (2003) New records of freeliving marine nematodes from Hong Kong, China. Journal of Ocean University of Qingdao 2, and Zou C. (2001) Research on free-living marine nematodes near Xiamen Island new and known species of family Comesomatidae (Nematoda). Journal of Oceanography in Taiwan Strait 20, [In Chinese.] Correspondence should be addressed to: F Semprucci Dipartimento di Scienze della Terra, della Vita e dell Ambiente (DiSTeVA), Università di Urbino, loc. Crocicchia, Urbino, Italy federica.semprucci@uniurb.it