Paraopisthosyllis alternocirra, San Martin & Hutchings, 2006

San Martin, G & Hutchings, PA, 2006, Eusyllinae (Polychaeta: Syllidae) from Australia with the Description of a New Genus and Fifteen New Species, Records of the Australian Museum 58, pp. 257-370 : 317-319

Paraopisthosyllis alternocirra n.sp.

Figs 50A–E, 51A–H, 52A–I

Opisthosyllis brevicirra .— Hartmann-Schröder, 1982: 57 (in part).

Material examined. HOLOTYPE ( AM W26734) AUSTRALIA: WESTERN AUSTRALIA: Red Bluff, Kalbarri , 27°42'S 114°09'E, mixed coralline algae, 4 m, coll. J.K. Lowry, 10 Jan 1984 . PARATYPES Red Bluff , Kalbarri, 27°42'S 114°09'E, round-leaved seagrass in shallow sand on rocky shore, 3.5 m, coll. R.T. Springthorpe, 10 Jan 1984, 3 ( AM W28366) ; Rocky shore, Red Bluff, Kalbarri, 27°42'S 114°09'E, dictyotalean alga from cave, 4 m, coll. J.K. Lowry, 10 Jan 1984, 4 ( AM W26784) ; Rocky shore, Red Bluff, Kalbarri, 27°42'S 114°09'E, brown algae from surf zone, 0.5 m, coll. H.E. Stoddart, 9 Jan 1984, 1 ( AM W26783) ; Red Bluff , Kalbarri, 27°42'S 114°09'E, mixed coralline algae, 4 m, coll. J.K. Lowry, 10 Jan 1984, 7 + 1 on SEM stub ( AM W28984) ; Inshore limestone reef, Ned’s Camp, Cape Range National Park, 21°59'S 113°55'E, sponge covered with epiphytes, sediment & muddy worm tubes, 1.5 m, coll. R.T. Springthorpe, 2 Jan 1984, 1 ( AM W28368) .

Additional material examined. WESTERN AUSTRALIA: Rockingham, Point Peron , 32°17'S 115°44'E 115, algae, intertidal, coll. G. Hartmann-Schröder, 1 ( HMZ P-17049); identified by Hartmann- Schröder as Opisthosyllis brevicirra .

Description. Complete specimen. Body anteriorly broad, tapered posteriorly ( Fig. 52A), 6.7 mm long, 0.5 mm wide, with 59 chaetigers. Dark area of pigment dorsally on each segment, sometimes divided into 2 dorsal areas, anterior and posterior lateral areas; dark areas forming incomplete transverse row on posterior segments ( Fig. 50A–C). Small, scattered papillae on lateral and ventral surfaces, more numerous on dorsum ( Figs 50A,C, 52C,D). Prostomium oval, 4 small eyes arranged in open trapezoidal pattern, almost in straight line; lateral antennae inserted near anterior margin, oval, slightly rugose, shorter than combined length of prostomium and palps, median antenna similar to lateral but thicker, slightly longer, provided with dark inclusions, inserted slightly posteriorly to lateral ones, in front of eyes ( Fig. 50A). Palps broad, longer than prostomium, ventrally folded ( Figs 50D,E, 52C). Peristomium shorter than subsequent segments; tentacular cirri similar in shape to lateral antennae, but larger. Dorsal cirri of chaetiger 1 distally inflated, club-shaped, provided with dark inclusions, and located laterodorsally, anteriorly directed, partially covering prostomium ( Fig. 50A,C,D); dorsal cirri of chaetigers 4 and 6 similar, but less inflated and more laterally inserted, subsequent dorsal cirri club-shaped, not as inflated as those of chaetigers 1, 4 and 6, without dark inclusions; alternating dorsal cirri laterodorsally located and others slightly smaller, more laterally located, cirri becoming smaller posteriorly ( Fig. 50C,D). Dorsal cirri with cirrophores. Anterior parapodia with 7 compound, heterogomph chaetae, shafts with some spines on distal margin, and curved blades; 2 dorsalmost compound chaetae with relatively short, bidentate blades, with both teeth close to each other, and short spines on margin ( Fig. 51C), 16 µm long; remaining compound chaetae with smooth, unidentate blades ( Figs 51C, 52G), within fascicle slight dorsoventral gradation in length of blade, 22 µm in length dorsally, 17 µm in length ventrally. Progressively along body, chaetal blades becoming shorter and less bidentate; posterior parapodia with 6 compound chaetae, decreasing to 3 on posteriormost chaetigers, blades slightly hooked, smooth on margin, unidentate ( Figs 51G, 52H), blades 15 µm in length dorsally, 10 µm in length ventrally. Dorsal simple chaetae slender, unidentate, smooth ( Fig. 51F), present on posterior chaetigers ( Fig. 52I). Ventral simple chaetae smooth, distally bent, unidentate, present on most posterior parapodia ( Figs 51H, 52I). Anterior parapodia with 3–4 aciculae, distally rounded, single acicula on posterior parapodia ( Fig. 51E). Pharynx wide, through 3–4 segments; pharyngeal tooth located about one third from anterior margin of pharynx ( Fig. 51A). Margin of pharynx with 10 papillae ( Figs 51A, 52E), each papilla with short cilia ( Fig. 52F). Proventricle, longer than pharynx, extending through 3 segments, with 25–30 muscle cell rows. Pygidium small, with 2 anal cirri with dark inclusions, inflated and oval ( Fig. 50B).

Remarks. This species is similar to P. brevicirra Hartmann- Schröder, 1979 (see below) but P. alternocirra has short and long dorsal cirri alternating along the anterior part of the body, distinct dark inclusions on the median antenna and large dorsal cirri, a colour pattern, and some dorsal compound chaetae on anterior and midbody parapodia with bidentate blades. In contrast, P. brevicirra has only unidentate chaetae, dorsal cirri not as inflated and lacks dark inclusions on the antennae and cirri, and is colourless. The specimen reported as Opisthosyllis brevicirra by Hartmann- Schröder (1982) belongs to this new species and differs from the holotype of the taxon.

Habitat. Occurring in algae, seagrasses, and sponges; from intertidal to shallow depths.

Distribution. Australia (Western Australia).

Etymology. The specific name refers to the alternating sizes of the dorsal cirri along the body.