Namalycastis solenotognatha, Pradhan & Villalobos-Guerrero & Mohapatra, 2025

Pradhan, Jyoshna, Villalobos-Guerrero, Tulio F. & Mohapatra, Anil, 2025, Description of two new species of nereidids (Annelida: Nereididae) from West Bengal, India, Bay of Bengal, Zootaxa 5729 (2), pp. 335-348 : 338-341

Namalycastis solenotognatha sp. nov.

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Fig. 2

Type material. India, Bay of Bengal. Holotype: EBRC /ZSI/An-18595, Bankiput, Purba Medinipur ( 21°44’34.6”N 87°50’29.3”E), West Bengal, 03 May 2025, mudflat, coll. J. Pradhan. Paratype: One specimen ( EBRC /ZSI/An- 18596), same collection data as for holotype .

Additional material. India, Bay of Bengal. Three specimens ( EBRC /ZSI/An-18597), 13 June 2025, same collection data as for holotype .

Diagnosis. Epidermal pigmentation present. Prostomium anteriorly shallowly cleft. Eyes subequal; anterior pair sub-rounded, posterior pair oval. Antennae extending to tip of palpophore. Posterodorsal tentacular cirri extending up to chaetiger 2. Jaws with many inner canals (more than 20). Notochaetae absent. Supra-preacicular neurochaetae with heterogomph spinigers anteriorly. Subacicular neurochaetae with heterogomph falcigers smooth-bladed (very few teeth proximally). Sesquigomph and heterogomph spinigers with fine serrations proximally. Pygidium multi-incised, ring-shaped.

Description. Holotype complete, in good condition, 108.8 (18.8–79.2) mm TL, 15.9 (6.0–8.8) mm L15, 2.4 (2.3–3.7) mm W15, and 206 (170–191) chaetigers. Body widest mid-anteriorly, gradually tapering towards posterior end. General body colour light brown throughout, with lighter brown epidermal pigmentation antero-dorsally.

Prostomium campanulate; anterior region distally indented, trapezoid-shaped, twice longer than posterior region ( Fig. 2A ); longitudinal groove shallow, extending from tip to mid-posterior prostomium; anterolateral gap between antenna and palpophore narrow, as wide as basal diameter of antennae. Nuchal organs deeply embedded.

Palpophores barrel-shaped, short ( Fig. 2A ), 1.1 times as long as wide, three-quarters as long as prostomium; sub-distal transverse groove indistinct. Palpostyles spherical, one-third as long as palpophore.

Antennae tapered, conical, as long as prostomial posterior region, nearly extending to tip of the palpophores, aligned over inner edge of palps; antennae separated by gap 5 times as wide as their basal diameter.

Paired eyes in oblique arrangement, coalesced, black ( Fig. 2A ). Anterior pair sub-rounded, eye diameter 1.8 times wider than basal diameter of antennae; lenses oval, greyish, placed mid-laterally. Posterior pair of eyes oval, with diameter 1.5 times wider than antennae; lenses indistinct, placed posterolaterally.

Tentacular belt as long as chaetiger 1 ( Fig. 2A ), with straight anterior margin. Tentacular cirrostyles smooth; anterior cirrostyles anterolateral and posterior cirrostyles lateral to tentacular belt ( Fig. 2B ). Anterodorsal cirrostyles extending backwards to border between chaetigers 1 and 2; antero-ventral cirrostyles extending upwards to tip of palpophore. Posterodorsal cirrostyles extending backwards to chaetiger 2; posteroventral cirrostyles extending sideward to proximal lateral base of prostomial posterior region. Dorsal and ventral cirrophores distinct, cylindrical.

Proboscis everted, with maxillary and oral rings cylindrical, wider than long. Jaws mostly dark amber; 9 (9−12) teeth: 5 (5–7) subterminal teeth, 4 (4–5) ensheathed proximally ( Fig. 2C ); more than 20 canals emerging from pulp cavity ( Fig. 2D ).

Dorsal cirri composed of barely-distinct cirrostyles and enlarged cirrophores ( Fig. 2E–I ), slightly longer than neuroacicular ligule in anterior chaetigers ( Fig. 2 E−G), twice as long as ligule in following chaetigers ( Fig. 2H, I ). Dorsal cirrostyles cirriform, attached distally to dorsal cirrophore throughout body. Dorsal cirrophore increasing in length posteriorly, expanding from about chaetiger 8 or 9 ( Fig. 2 E−G); markedly enlarged and pennant-like in middle chaetigers ( Fig. 2H ), elongated and ribbon-shaped in posterior chaetigers ( Fig. 2I ).

Neuroacicular ligule sub-conical, distally blunt, bilobed ( Fig. 2E–I ). Neuropodial superior lobe very short, papilliform. Neuropodial inferior lobe globular.

Ventral cirri short ( Fig. 2E–I ), one-half length of neuroacicular ligule at anterior chaetigers, one-third length in following chaetigers.

Aciculae mostly black throughout body. Notochaetae absent throughout body. Supracicular neurochaetae consisting of post-acicular sesquigomph spinigers ( Fig. 2J ), pre-acicular heterogomph spinigers ( Fig. 2K ), and pre-acicular heterogomph falcigers; few sesquigomph spinigers and up to 6 heterogomph falcigers present throughout, single heterogomph spiniger present in anterior chaetigers only. Subacicular neurochaetae consisting of post-acicular heterogomph spinigers and pre-acicular heterogomph falcigers ( Fig. 2L, M ), both present throughout.

Blade of sesquigomph spinigers finely serrated throughout body, proximal serrations of even length but slightly thicker. Blade of heterogomph spinigers coarsely serrated proximally. Blade of heterogomph falcigers long (b/a ratio: 1.3–1.9); supracicular finely serrated, with 4 well-developed proximal teeth anteriorly, increasing to 7–8 teeth posteriorly; subacicular nearly smooth bladed, with 2 barely-developed proximal teeth anteriorly ( Fig. 2L ), increasing to 6 proximal teeth posteriorly ( Fig. 2M ). Shaft of heterogomph falcigers camerated, with cavity divided sub-distally into four distinct longitudinal partitions; boss of regular size.

Pygidium multi-incised, ring-shaped, reddish-brown ( Fig. 2N ); anal cirri ventrolateral, as long as last 4 (2−4) chaetigers.

Variations. Total body length: 18.8–79.2 mm. Length to chaetiger 15: 6.1–8.8 mm. Body width at chaetiger 15: 2.3–3.7 mm. Number of total chaetigers: 49–191. Longest tentacular cirri extending to chaetiger 1–2. Jaws with 4–5 teeth. Anal cirri as long as last 2–4 chaetigers.

Anatomical anomalies. One specimen ( 18.8 mm long, 2.3 mm wide, 49 chaetigers) with pygidium showing four ventral anal cirri with distinct cirrophore, one located on the right side and the other three on the left side ( Fig. 2O, P ).

Etymology. The species’ name solenotognatha is a combination of the Greek words solenotos (channelled) and gnatha (jaw), indicating that members of the species have jaws with numerous canals emerging from the pulp cavity. Declination is feminine.

Type locality. Bankiput ( 21°44’34.6’’N 87°50’29.3’’E), West Bengal, India ( Fig. 1 ) .

Habitat. Mudflat with an abundance of hard substratum, particularly bricks ( Fig. 1A, B ). Individuals dwelled inside the bricks and were associated with other lower invertebrates, such as sea slugs, small molluscs, crabs, and isopods.

Distribution. This species is only known from the type locality.

Remarks. Six species of Namalycastis have been reported from Indian waters, plus the addition of the new one described in the present study: Namalycastis abiuma (Grube, 1871) from Brazil, N. solenotognatha sp. nov. from Eastern India, N. fauveli Nageswara Rao, 1981 from Eastern India, N. glasbyi Fernando & Rajasekaran, 2007 from Western India, N. indica ( Southern, 1921) from Eastern India, N. jaya Magesh, Kvist & Glasby, 2012 from Western India, and N. meraukensis (Horst, 1918) from Papua New Guinea. Nevertheless, the latter species is considered very similar to N. abiuma and thus treated as part of the nominal species group ( Glasby 1999).

Among those species, N. solenotognatha sp. nov. differs from its congeners by the absence of notochaetae (except N. abiuma and N. jaya ) and the presence of heterogomph spinigers in supra-preacicular neurochaeta in anterior chaetigers. Additionally, N. solenotognatha sp. nov. can be distinguished from N. fauveli by the boss of regular size in heterogomph falcigers, in contrast to that markedly elongated in N. fauveli . Also, N. solenotognatha sp. nov. has longer antennae (extending over the tip of palps) than N. fauveli (extending over the mid-palps). Moreover, in N. solenotognatha sp. nov. the postero-dorsal tentacular cirri are shorter (extending to chaetigers 2−3) than N. glasbyi (extending to chaetigers 4−5) and N. indica (extending to chaetigers 5−6). Also, the anterior and posterior eyes of N. solenotognatha sp. nov. are subequal, whereas the posterior eyes are much smaller than the anterior ones in N. glasby . Finally, N. solenotognatha sp. nov. has a multi-incised pygidium, unlike that tripartite in N. indica .

Namalycastis solenotognatha sp. nov. mostly resembles N. abiuma and N. jaya , although it can differ in several features. In N. solenotognatha sp. nov., the anterior and posterior eyes are similar; whereas in N. jaya , the posterior pair is much smaller than the anterior pair. The jaws of N. solenotognatha sp. nov. comprise 20 or more inner canals; in contrast, there are up to 12 canals in N. jaya . In N. solenotognatha sp. nov., the blades of heterogomph spinigers are finely serrated, whereas in N. jaya , they are coarsely serrated proximally. In N. solenotognatha sp. nov. the neuropodial superior lobe is smaller than the neuropodial inferior lobe, unlike the superior lobe of N. jaya , which is longer than the inferior lobe. Finally, the pygidium is reddish-brown in N. solenotognatha sp. nov., whereas it is black in N. jaya .

Furthermore, N. solenotognatha sp. nov. can be distinguished from N. abiuma s. str. (fide Alves et al. 2024, also Glasby et al. 1999) by the smooth-bladed subacicular heterogomph falcigers of neurochaetae in the anterior parapodia, in contrast to those of N. abiuma s. str., which are finely serrated. Likewise, the neuropodial superior lobe is papilliform throughout the body in N. solenotognatha sp. nov., whereas it is bluntly conical at least in chaetiger 10 of N. abiuma s. str. Also, the posterodorsal tentacular cirri of N. solenotognatha sp. nov. are shorter (extending up to chaetiger 2) than those in N. abiuma s. str. (extending to chaetigers 3−5). In N. solenotognatha sp. nov., the pygidium is ring-shaped, whereas it is button-shaped in N. abiuma s. str. Finally, N. solenotognatha sp. nov. is a much longer species (up to 110 mm with up to 206 chaetigers) than N. abiuma s. str. (usually up to 50 mm with 150 chaetigers). Likely, N. abiuma s. str. is not distributed in Indian waters.

Figures

FIGURE 1. Collection localities and habitats of the new species described in the study from the coastal region of West Bengal in the Bay of Bengal, Eastern India. A. Active sampling of specimens collected by hand shovel during peak low tide time. B. Habitat of Namalycastis solenotognatha sp. nov., with soft sediments and clay bricks. C. Habitat of Nereis dhritiae sp. nov., with heavily biofouled wooden dock piles.

FIGURE 2. Namalycastis solenotognatha sp. nov. from Bankiput, Purba Medinipur, West Bengal, India. A–N. Holotype (EBRC/ZSI/An-18595). O–P. Paratype (EBRC/ZSI/An-18596). A. Anterior end and everted proboscis in dorsal view. B. Anterior end and everted proboscis in ventral view. C. Right jaw in ventral view, arrow points to inner canal. D. Right jaw in ventral view, arrow points to canals emerging from pulp cavity. E–I. Parapodia in anterior view. J. sesquigomph spinigers from supracicular neurochaetae (parapodia 2). K. Heterogomph spinigers from supracicular neurochaetae (parapodium 2). L. Pre-acicular heterogomph falcigers from subacicular neurochaetae (parapodium 50). M. Pre-acicular heterogomph falcigers from subacicular neurochaetae (parapodium 130). N. Pygidium in ventral view. O–P. Pygidium showing anal cirri with distinct cirrophores (grey arrow) and cirrostyles (white arrow) in ventral and dorsal views, respectively. Scale bars: A, B= 1 mm; C= 0.15 mm; D= 0.02 mm; E= 0.1 mm; F–I= 0.15 mm; J–K= 0.025 mm; L–M= 0.02 mm; N= 1 mm; O–P= 0.5 mm.