Opisthosyllis japonica Imajima, 1966

Martín, Guillermo San, Hutchings, Pat & Aguado, María Teresa, 2008, Syllinae (Polychaeta, Syllidae) from Australia. Part. 2. Genera Inermosyllis, Megasyllis n. gen., Opisthosyllis, and Trypanosyllis, Zootaxa 1840, pp. 1-53 : 26

Opisthosyllis japonica Imajima, 1966

Figs 17C–F, 18A–I, 19A–F, 20A

Opisthosyllis japonica Imajima, 1966b: 226 , text-fig. 40 a–p.– Hartmann-Schröder 1980: 48, figs 27–32.

Material examined. AUSTRALIA, WESTERN AUSTRALIA: Kimberley region, reef S of Lucas Island, Brunswick Bay , 15° 16'S, 124° 29'E, 2 m, coll. P.A. Hutchings, 24 Jul 1988, 2 (1 SEM), ( AM W31383) ; East Montalivet Island , 15° 06'S, 125° 18'E, 6 m, coll. P.A. Hutchings, 16 Jul 1988, 1 ( AM W31381) ; Condillac Island , 14° 06'S, 125° 33'E, 6 m, sand with scattered bommies, coll. P.A. Hutchings, 16 Jul 1988, 1 ( AM W31382) .

Description. Longest specimen, 10 mm long, 0.5 mm wide, 71 chaetigers, colourless; Japanese specimens up to 40 mm, 1.3 mm wide, 173 chaetigers (fide Imajima, 1966b). Prostomium oval, partially covered by peristomium; 4 large eyes in trapezoidal arrangement ( Fig. 18A). Median antenna inserted between anterior eyes, longer than combined length of prostomium and palps, with about 30 articles; lateral antennae inserted in front of anterior eyes, shorter than median antenna, with 15–17 articles ( Fig. 18A). Palps broad, similar in length to prostomium. Peristomium similar in length to following segments; dorsal tentacular cirri with 35 articles, longer than antennae and ventral tentacular cirri (with about 15 articles). Dorsal cirri of chaetiger 1 distinctly longer, with 50–56 articles, following ones, alternating long (25–30 at midbody) and short (13–15 articles). Antennae and tentacular and dorsal cirri slender, whip-shaped ( Figs 17C, D, 18A). Ventral cirri digitiform, shorter than parapodial lobes. Parapodia distally bilobed, with pre- and post-chaetal lobes ( Fig. 18A), pre-chaetal lobe digitiform, longer than post-chaetal ( Figs 17D–E, 18A). Anterior compound heterogomph chaetae, 10–15, short, falcigerous bidentate blades (21 µm dorsally to 13 µm ventrally), small proximal tooth and short spines on margin ( Figs 17E, F, 18B, 19A), number of chaetae progressively decreasing posteriorly, as shafts becoming thicker, sub-distally enlarged, and blades becoming shorter, unidentate, with few, short spines on margin ( Figs 18E, H, 19B–D); 1 (sometimes 2) dorsal chaeta on each parapodium loosing blade and becoming thick, forming simple chaeta ( Figs 18D, G, 19B, D, 20A). Posterior parapodia with 1–2, simple and 3–5 compound thick chaetae with sub-distally enlarged, smooth shafts and short unidentate blades ( Figs 18G, H, 19E, F, 20A), 23– 20 µm long, with 2–4 short straight spines. Anterior aciculae 2–3, slender, one straight, other distally broad ( Fig. 18C), decreasing progressively ( Fig. 18F) to solitary, distally rounded acicula from mid-posterior parapodia ( Fig. 18I). Pharynx long, starting at chaetiger 2–3, extending through 7–8 segments; pharyngeal tooth located near posterior end of pharynx ( Fig. 18A). Proventricle similar in length or slightly shorter to pharynx, through 5–6 segments, with 55–60 muscle cell rows. Pygidium not seen.

Habitat. Sand, algae, coralline concretions, ascidians; intertidal and shallow substrates.

Distribution. Japan, Australia (Western Australia).