Syllis okadai Fauvel, 1934

Syllis okadai Fauvel, 1934 View in CoL Figs 18–20 View FIGURE 18 View FIGURE 19 View FIGURE 20

Syllis okadai Fauvel, 1934 View in CoL ; pp. 307–309, text-figs. 1, 2.

Syllis okadai Fauvel, 1953 View in CoL ; pp. 152–153, fig. 76.

Typosyllis okadai Imajima and Hartman, 1964 View in CoL ; p. 137.

Typosyllis okadai Imajima, 1966 View in CoL ; pp. 268–270, text-fig. 56.

Syllis okadai Aguado, Nygren and Siddall, 2007 View in CoL ; 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 View FIGURE 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 View FIGURE 18 ). Dorsal side with four rows of white spots, two spots per row and segment, rows located more ventrally fade out posteriorly ( Fig. 18A–E View FIGURE 18 ). Head appendages (except palps), pygidium and cirri white ( Fig. 18A, D–E View FIGURE 18 ). 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 View FIGURE 18 , 19B View FIGURE 19 ). Two brown palpi form the anterior part of the prostomium ( Fig. 18A, D–E View FIGURE 18 ). Grooves of cilia around the eyes, nuchal organs located at the posterior end of the prostomium, between prostomium and first segment ( Fig. 20B, E View FIGURE 20 ).

Two pairs of tentacular cirri ( Fig. 20B View FIGURE 20 ). Dorsal cirri longer in anterior region, become gradually shorter towards posterior end ( Fig. 18A–E View FIGURE 18 ). Annulated dorsal cirri ( Figs 19B, F View FIGURE 19 , 20A–D, F View FIGURE 20 ) with around 9 annulations. Pygidium with two short, white anal cirri ( Fig. 20C, F View FIGURE 20 ). Anterior chaetae compound, 10–14 per parapodium ( Fig. 21B–G View FIGURE 21 ). 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 View FIGURE 21 ). Posterior parapodia with eight compound chaetae with short and broad shafts, bidentate ( Fig. 21E–G View FIGURE 21 ). 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 View FIGURE 21 ). Last chaetiger with only eight chaetae (six compound, two simple).

Reproduction. Schizogamy by scissiparity. Adult specimens developing each a dicerous stolon ( Fig. 19A–E View FIGURE 19 ). 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 View FIGURE 19 ). Two lateral antennae developed, small ( Fig. 19C, E View FIGURE 19 ). Female stolons with green ovules visible by transparency ( Fig. 19E View FIGURE 19 ). Male stolons with beige sperm visible by transparency ( Fig. 19B View FIGURE 19 ). Pygidium with pair of small and conical anal cirri. Compound chaetae present. Notoaciculae present in developing and mature stolons ( Fig. 19A–E View FIGURE 19 ). Stock forming a pair of tail primordia ventrally while the stolon is still attached to the parental stock ( Fig. 19D View FIGURE 19 ). The tail primordia ( Fig. 19F View FIGURE 19 ) 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.