Opisthosyllis simpliseta Hartmann-Schröder, 1981

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 : 32-34

Opisthosyllis simpliseta Hartmann-Schröder, 1981

Figs 23E, F, 24A–D, 25A–F, 26A–D

Opisthosyllis simpliseta Hartmann-Schröder, 1981: 25 , figs 19–27 (as Opisthosyllis simplisetis sic ).

Material examined. AUSTRALIA, WESTERN AUSTRALIA: Cervantes, 30º 29’S, 115º 04’E, Posidonia with fine sand, holotype (HZM P–16476); Off south end of Long Island , Beacon Island , 28° 28' 48"S, 113° 46' 18"E, 5 m, dead coral substrate, covered in coralline algae, coll. P.A. Hutchings, 25 May 1994, 1 on SEM stub, ( AM W31431) .

Description. Longest specimen (AM W31431) 55 mm long, 1.4 mm wide, about 210 chaetigers, almost complete. Body long, slender, yellowish in alcohol, opaque, without colour markings, with well-defined segments ( Figs 23E, F, 24A). Prostomium oval, partially covered by peristomium ( Fig. 24A); 4 eyes in trapezoidal arrangement. Median antenna inserted between posterior eyes, near posterior margin of prostomium, similar in length to combined length of prostomium and palps, with 10–12 articles; lateral antennae inserted in front of anterior eyes, similar in length or slightly longer than median antenna, with 11–14 articles. Palps broad, short, ventrally folded. Peristomium smaller and shorter than subsequent segments ( Fig. 24A); dorsal tentacular cirri longer than antennae, with 16–18 articles, slightly longer than ventral ones. Anterior dorsal cirri long, with 18–20 articles, becoming shorter immediately ( Fig. 24A), alternating long (14–16 articles) and short (9–13 articles) cirri ( Figs 23E, F, 24A) at midbody; dorsal cirri shorter than body width, thick, spindleshaped. Ventral cirri digitiform, shorter than parapodial lobes. Parapodia distally bilobed, with pre- and postchaetal lobes ( Figs 24B–D, 26A). Anterior parapodia with about 10 compound chaetae; shafts heterogomph, with few subdistal spines, blades short, falcigerous, bidentate with proximal tooth small and short marginal spines, 22µm long above, 17µm long below; number of chaetae progressively diminishing posteriorly, together with shafts becoming thicker ( Fig. 24B–D), subdistally enlarged, and blades becoming shorter, unidentate, and marginally smoother ( Fig. 25B); most dorsal chaeta on each parapodium loosing blades and becoming thick, simple chaeta ( Figs 25D, 26C). Mid-posterior parapodia with single thick simple chaeta and 3–4 compound with short blades; posterior parapodia with single simple chaeta and 2–3 compound with thick, subdistally enlarged, smooth shafts and short blades, 27– 21 µm long, slightly bidentate with small proximal tooth or totally unidentate ( Figs 25E, 26D). Anterior aciculae 4–5, slender, and distally pointed, diminishing progressively to solitary midbody acicula, distally broad ( Fig. 25C, F). Pharynx wide, starting on chaetiger 2– 3, extending through 6–7 segments; pharyngeal tooth located near posterior end of pharynx ( Fig. 24A). Proventricle similar in length to pharynx, through about 6–7 segments, with 38–42 muscle cell rows. Pygidium not seen.

Habitat. Among seagrasses and dead corals; intertidal and shallow waters.

Distribution. Australia (Western Australia).