Opisthodonta hanneloreae, 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 : 302-303

Opisthodonta hanneloreae n.sp.

Fig. 37A–G

Material examined. HOLOTYPE ( AM W28393). AUSTRALIA: WESTERN AUSTRALIA: Wallabi Group of Is. , 28°23.99'S 113°46.73'E, shell debris from scallop beds, 39 m, coll. P.A. Hutchings on WA FRV

Flinders, 30 May 1994. PARATYPES Wallabi Group of Is. , 28°24'S 113°46.26'E, scallop beds, shell debris, 35 m, coll. P.A. Hutchings on WAFRV Flinders, 30 May 1994, few ( AM W28372); Off S end of Long Is. Beacon Is. 28°28.8'S 113°46.3'E, dead coral substrate covered in coralline algae, 4.5 m, coll. P.A. Hutchings , 25 May 1994, 1 ( AM W28950); Goss Passage , Beacon Is. 28°25.5'S 113°47'E, dead coral substrate, in fine sediment at foot of reef slope, 33 m, coll. P.A. Hutchings , 23 May 1994, 1 ( AM W28951) .

Description. Body fragile, all fragmented specimens, strongly convex dorsally, colourless, longest anterior fragment 2.8 mm long, 0.6 mm wide, with 18 chaetigers. Prostomium oval, with 4 eyes in open trapezoidal arrangement and sometimes 2 anterior eyespots; median antenna inserted in front of line between anterior eyes, about twice as long as combined length of prostomium and palps; lateral antennae inserted near anterior margin, about half length of median antenna ( Fig. 37A). Palps trapezoidal, sometimes ventrally folded, slightly longer than prostomium. Peristomium similar in length to following segments; dorsal tentacular cirri long, filiform, longer than median antenna, ventral tentacular cirri about one third length of dorsal cirri. Dorsal cirri, as well as antennae and tentacular cirri, smooth, filiform, alternating irregularly, long cirri, longer than body width, and short cirri, shorter than body width ( Fig. 37A). Parapodial lobes rectangular, ending with pre-chaetal lobe. Ventral cirri large, triangular, partially fused to parapodial lobes on anterior parapodia, with some granular inclusions, becoming digitiform, not fused to parapodial lobes, on subsequent segments. Compound chaetae compound heterogomph, shafts distally spinose, and two kinds of blades, long, spiniger-like chaetae, anteriorly bifid ( Fig. 37B), apparently unidentate on posterior parapodia ( Fig. 37D), and bidentate falcigers, elongate, with short spines on margin and margins of blades weakly convex on anterior parapodia, bidentate, with unequal teeth, proximal tooth longer and broader than distal tooth ( Fig. 37C), becoming more marked on posterior chaetae ( Fig. 37E). Anterior parapodia with about 3 spiniger-like chaetae, blades 90–175 µm in length; and about 50 falcigers with blades 25–27 µm in length; progressively posteriorly number of compound chaetae decreasing to 1–2 spinigerlike, about 105 µm in length, smooth and unidentate, and 25 falcigers, 25–22 µm in length, on mid-posterior parapodia. Simple dorsal and ventral chaetae not seen. Aciculae distally slightly enlarged, ending in button, 4 on most anterior parapodia ( Fig. 37F), reducing to 2 on midposterior parapodia, one large and other slender ( Fig. 37G). Pharynx long and slender, through about 11 segments; pharyngeal tooth long and large, oval, located slightly anteriorly to middle of pharynx ( Fig. 37A). Proventricle large, through about 6 segments, with 23 muscle cell rows. Details of posterior end unknown.

Remarks. Opisthodontha hanneloreae n.sp. is similar to O. melaenonephra , but lacks any colour pattern, the spiniger-like chaetae are distinctly longer and more slender, unidentate from midbody onwards. Opisthodonta morena Langerhans, 1879 (see above), and O. mitchelli Kudenov & Harris (1995) have much shorter spiniger-like chaetae than O. hanneloreae .

Habitat. Occurring in dead corals and in shell debris, in shallow water.

Distribution. Australia (Western Australia).

Etymology. The species is named after Dr Hannelore Paxton an Australian polychaetologist.