Syllis okadai Fauvel 1934

Syllis okadai Fauvel, 1934 Figs 18–20 Syllis okadai Fauvel, 1934; pp. 307–309, text-figs. 1, 2. Syllis okadai Fauvel, 1953; pp. 152–153, fig. 76. Typosyllis okadai Imajima and Hartman, 1964; p. 137. Typosyllis okadai Imajima, 1966; pp. 268–270, text-fig. 56. Syllis okadai Aguado, Nygren and Siddall, 2007; pp. 556, fig. 1. Material examined. Two specimens (NSMT-Pol 113617), Japan, Misaki: Araihama Beach, Sagami Bay, Misaki Marine Biological Station, 35°09'36.1"N 139°36'40.1"E, 2–5 m, coll. Oguchi & Aguado, 2019. Additional material (ZMUG 32501): Japan, Misaki: Sagami Bay, Misaki Marine Biological Station, 35°09'36.1"N 139°36'40.1"E, 2–5 m, coll. Aguado & Sato 2024. Description. Largest specimen complete, 11.8 mm long and 0.5 mm wide without chaetae. 82 chaetigers, prostomium and pygidium. Body subcylindrical, broad, ventrally flattened (Fig. 18). Segments 1–2 dark brown, segments 3–6 white, segments 7–9 dark brown, rest is dark red, segments ventrally white (Fig. 18A–E). Dorsal side with four rows of white spots, two spots per row and segment, rows located more ventrally fade out posteriorly (Fig. 18A–E). Head appendages (except palps), pygidium and cirri white (Fig. 18A, D–E). Prostomium with one median antenna located at the posterior end, two pairs of orange/red eyes and a pair of lateral antennae (Figs 18A, D–E, 19B). Two brown palpi form the anterior part of the prostomium (Fig. 18A, D–E). Grooves of cilia around the eyes, nuchal organs located at the posterior end of the prostomium, between prostomium and first segment (Fig. 20B, E). Two pairs of tentacular cirri (Fig. 20B). Dorsal cirri longer in anterior region, become gradually shorter towards posterior end (Fig. 18A–E). Annulated dorsal cirri (Figs 19B, F, 20A–D, F) with around 9 annulations. Pygidium with two short, white anal cirri (Fig. 20C, F). Anterior chaetae compound, 10–14 per parapodium (Fig. 21B–G). Anterior chaetae with long and slender shafts, denticles at the distal end of the shaft, large blades with serrations along the cutting margin and two distal teeth, proximal one slightly larger than distal one (Fig. 21C–D). Posterior parapodia with eight compound chaetae with short and broad shafts, bidentate (Fig. 21E–G). Additionally, posterior parapodia with two short and broad simple chaetae, one dorsal with a subdistal secondary tooth and one unidentate, distally curved ventral (Fig. 21A, E–G). Last chaetiger with only eight chaetae (six compound, two simple). Reproduction. Schizogamy by scissiparity. Adult specimens developing each a dicerous stolon (Fig. 19A–E). Stolon with 14–21 body segments and pygidium. Stolon with two pairs of orange/red eyes, located laterally, one pair more dorsally, one more ventrally (Fig. 19A–E). Two lateral antennae developed, small (Fig. 19C, E). Female stolons with green ovules visible by transparency (Fig. 19E). Male stolons with beige sperm visible by transparency (Fig. 19B). Pygidium with pair of small and conical anal cirri. Compound chaetae present. Notoaciculae present in developing and mature stolons (Fig. 19A–E). Stock forming a pair of tail primordia ventrally while the stolon is still attached to the parental stock (Fig. 19D). The tail primordia (Fig. 19F) fuse to form a new pygidium after the detachment of stolon. Habitat. Rocky shorelines, shallow waters 2–5 m deep, on algae and coral rubble. Remarks. Syllis okadai is distinguished by a unique colour pattern (live and preserved specimens) and specially shaped compound chaetae in both the anterior and posterior regions. Additionally, the ciliated grooves around the eyes, a newly identified feature, were not mentioned in the original description. Apart from the newly identified features, the examined specimens closely match the original description. Distribution. Cambodia, Andaman Islands; Gulf of Siam; Seto, Manazuru and Misaki, Japan.