Clavisyllis tenjini, Cejp & Jimi & Aguado, 2023

Cejp, Benjamin, Jimi, Naoto & Aguado, M. Teresa, 2023, Another piece for the syllid puzzle: A new species from Japan and its mitochondrial genome reveal the enigmatic Clavisyllis (Phyllodocida: Syllidae) as a member of Eusyllinae, Zootaxa 5244 (4), pp. 341-360 : 350-352

Clavisyllis tenjini n. sp.

Cejp, Jimi & Aguado

Figs. 3–8

Material examined: Four specimens: NSMT-Pol H-901 (holotype), NSMT-Pol P-902 (paratype 1), MNCN 16.01 /17366 (paratype 2); ZMUG 30258 (paratype 3). Japan, Ogasawara Islands , Chichijima Island, (27°05′39.7″N 142°11′42.4″E), light trap, coll. NJ by hand, 24 May 2015 .

Description: Holotype (NSMT-Pol H-901) 13,6 mm long, 62 chaetigers. Paratype 1 (NSMT-Pol P-902) 14,4 mm long, 62 chaetigers. Paratype 2 (incomplete) 11,2 mm long, 55 chaetigers (about 8–10 additional posterior chaetigers were used for molecular analyses; MNCN 16.01/17366). Paratype 3 cut in half and prepared for SEM (ZMUG 30258) (anterior part ca. 3,3 mm, ~21 chaetigers; posterior part 4,1 mm, ~26 chaetigers; overall around 7,4 mm and ~47 chaetigers).

Body broad, elongated, dorsally arched ( Fig. 3A ). Dorsal surface of anterior segments with bunches of cilia ( Figs 4A–C , 7E ). Dorsal side covered at the sides with ovoid to round dorsal cirri, leaving an uncovered space in the middle along the anterior-posterior axis ( Figs. 3A, C–D , 5A–F ). From dorsal, parapodia are visible where not covered by dorsal cirri. Colour of in 70% ethanol preserved specimens white, eyes red, tips of many dorsal cirri bright yellow-orange ( Figs. 3A–D , 5A–F ).

Prostomium rounded, with four eyes arranged in a rectangle ( Figs. 3B , 5A–B , 6A ). Two palps inserting ventrally, fused at the base. Two papillae at the anterior side of the base of the palps (ventral prostomial papillae in Figs. 6A–B ). Antennae lost in holotype, antennophores of lateral antennae above the papillae, between the anterior eyes, median antennophore in the middle between the posterior eyes ( Figs. 6A–B ). Antennae of paratype 2 large and ovoid ( Fig. 5A ); no antennae preserved in other specimens. Two ovate projections emerging laterally from the prostomium, at the level between anterior and posterior eyes ( Figs. 6A–B ). Lateral projections as long as antennae but thinner and without antennophore. Nuchal organs long, sinuous, reaching parallelly until the 7 th chaetiger on the dorsal side ( Figs. 3D , 4A ), strongly ciliated and attached to the dorsal surface ( Figs. 4B, C ). Dorsally, two anterior extensions of the nuchal organs emerge ( Figs. 3A–B , 5A–B, D–E , 6A–B ). Nuchal extensions in shape and size similar to palps, with pointy tips. Lateral projections and nuchal extensions of paratype 2 smaller than in the other specimens ( Fig. 5A ). Two pairs of ovoid to balloon-like tentacular cirri. Dorsal cirri shaped the same way as tentacular cirri. Cirri of paratype 1 smaller than those of other specimens ( Fig. 3A ). Surface of dorsal cirri with a reticulate pattern. Dorsal cirri inserting alternately more dorsally and more ventrally on the side of each segment ( Figs. 7A, D ). Parapodia with distinct upper lobe and ventral cirrus ovoid in shape, slightly larger than dorsal lobe ( Figs. 6C , 8C ), between which bundles of chaetae emerge ( Fig. 8C ). Number of chaetae per bundle around 10–15 in the anterior part, increasing towards the mid-body. Chaetae compound, heterogomph falcigers ( Figs. 8A–D ). Bidentate blades with teeth similar in size and shape. Cutting edge with spines; basal spines short, spines in the middle of the edge long, exceeding the tip of the blade. Blades all similar in length ( Figs. 6D , 8A–B ). Two pointed acicula per parapodium. From the 11 th chaetiger until the end, parapodia strongly enlarged notopodium lobes with additional natatory simple chaetae (epigamic reproductive modifications) ( Figs. 7C–D ). Proventricle 6 to 7 segments long, beginning in chaetiger 5–7. Pharyngeal tooth and/or trepan not seen. Pygidium with two cirrophores ( Fig. 7F ).

Distribution: Chichijima Island, Ogasawara Islands, Japan.

Reproduction: All four specimens show strongly modified midbody-posterior parapodia with natatory chaetae (elongated simple notochaetae), indicating the individuals were in reproductive state at the time of sampling. This provides evidence for an epigamic reproduction in this species.

Remarks: The characteristic ovoid, balloon like dorsal cirri with alternating insertion points are shared between all three species of Clavisyllis . The new species is larger than C. yongei ( Watson 2009) and roughly as long as C. alternata with approximately the same number of segments ( Aguado & San Martín 2008). Clavisyllis tenjini n. sp. also shares the shape of nuchal epaulettes with C. alternata , lacking however the unique and characteristic nuchal cirrus of the latter. Exclusive to the new species are the prominent nuchal extensions on the anterior end of the epaulettes, as well as lateral projections emerging from the sides of the prostomium. These morphological differences, together with the occurrence more than 4500 km far from the other Clavisyllis occurrences justify the designation to a new species.

The presence of a pharyngeal tooth and/or trepan could not be assessed since the specimens were not dissected. There are currently very few Clavisyllis specimens available: one for C. alternata , one for C. yongei and four for C. tenjini n. sp. (one not complete, another prepared for SEM). The presence/absence of a pharyngeal tooth and/or a trepan would not influence the description of C. tenjini n. sp. as a new species. Hence, we preferred to keep the anterior end of the specimens with all its unique characteristics (lateral projections and dorsal nuchal extensions) not dissected.

Etymology: The species name is dedicated to Tenjin (RDz), the patron or deity (kami) of academics, scholars and learners in Shinto religion of Japan.

Figures

FIGURE 3. A. Paratype 1, complete dorsal view; B. Holotype, anterior end; C. Paratype 2, anterior end, lateral view; D. Paratype 2, anterior end, dorsal view. Visible structures are labelled: a = antennae, dc = dorsal cirrus with coloured tip, lp = lateral projetions, mnp = modified notopodium, nex = nuchal extensions, snc = natatory notochaetae, snl = sinuous nuchal lappets, p = palps.

FIGURE 4. SEM pictures of paratype 3. A. anterior end, dorsal view; B. nuchal organs; C. anterior nuchal extensions; D. anterior end.

FIGURE 5. A. Paratype 2, anterior end; B. Paratype 1, anterior end; C. Paratype 2, anterior end, lateral view; D. Paratype 1, anterior end, lateral view; E. Paratype 1, anterior dorsal view; F. holotype, complete specimen. Visible structures are labelled: a = antennae, dc = dorsal cirrus with coloured tip, lp = lateral projetions, mnp = modified notopodium, nex = nuchal extensions, snc = natatory notochaetae, snl = sinuous nuchal lappets, p = palps.

FIGURE 6. A. Drawing of the anterior end of the holotype with indicated structures; B. SEM picture of the anterior end of paratype 3. Highlighted structures: orange—nuchal extensions, green—lateral projections, violet—palps, blue—papillae, yellow—antennophores; C. Midbody parapodium, anterior view; D. Midbody chaetae. Scales C: 100 um, D. 20 um.

FIGURE 7. SEM pictures of paratype 3. A. modified notopodia with natatory chaeta and dorsal cirri; B. dorsal cirri; C. anterior half, complete lateral view; D. posterior half, lateral view; E. body surface with bundles of cilia; F. posterior end.

FIGURE 8. SEM pictures of paratype 3. A, B, D. chaetae of anterior segments; C. parapodium of anterior segment (not modified and without natatory chaetae).