Pionosyllis rousei, 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 : 345-346

Pionosyllis rousei n.sp.

Fig. 74A–F

Material examined. HOLOTYPE ( AM W29230), TASMAN SEA: reef flat near Yoshin Maru Iwaki wreck, Elisabeth Reef , 29°55.48'S 159°01.18'E, Elisabeth & Middleton Reefs Expedition, St. 43, 14 Dec 1987 . PARATYPES 4 ( AM W28840), reef flat near Yoshin Maru Iwaki wreck, Elisabeth Reef , TASMAN SEA, 29°55.48'S 159°01.18'E, Elisabeth & Middleton Reefs Expedition, St. 43, 14 Dec 1987 .

Additional material examined. TASMAN SEA: Taupo Seamount , 33°16.51'S 156°09.09'E, limestone & sand bottom, 244 m, coll. J.K. Lowry, on RV Franklin, 2 May 1989, 3 ( AM W28836) .

Description. Holotype best preserved individual, incomplete specimen, 2.2 mm long, 0.6 mm wide, with 22 chaetigers. Body fragile, dorsally arched, cylindrical, without colour pattern, yellowish in alcohol. Prostomium oval, with 4 eyes in open trapezoidal arrangement. Antennae damaged; lateral antennae inserted near anterior margin of prostomium, median antenna inserted on middle of prostomium. Palps large, slightly longer than prostomium, free from each other ( Fig. 74A). Nuchal organs ciliated, extending to lateral margins of prostomium ( Fig. 74A). Peristomium dorsally reduced, covered by chaetiger 1. Anteriormost segments short, becoming longer from proventricle onwards. Left dorsal tentacular cirrus missing, right one appears broken; ventral tentacular cirri shorter than dorsal cirri. Dorsal cirri smooth, with distinct cirrophores, elongated, alternating irregularly long and short ( Fig. 74A), long cirri similar in length to body width, shorter cirri less than half length of longer ones. Parapodial lobes conical. Ventral cirri elongated, similar in length to parapodial lobes. Compound chaetae heterogomph, blades of two kinds, spiniger-like and falcigers. Midbody parapodia with 2 spiniger-like chaetae, with short spines on margin, distinctly bidentate, distal tooth hooked, and proximal tooth curved, with tendon contacting with margin, about 40–35 µm long ( Fig. 74C), and 8–11 falcigers, strongly bidentate, long and hooked distal tooth and long, curved proximal tooth, provided with distinct tendon contacting with edge of blade, slight dorsoventral gradation in length of blades within fascicle, 25 µm dorsally and 15 µm ventrally ( Fig. 74D), with thin spines on margin. Anteriormost parapodia with 1–2 distinctly long, slender, spiniger-like chaetae present, blades about 86 µm in length, bidentate, with both blades similar in size, proximal tooth slightly recurved, but without tendon ( Fig. 74B). Dorsal and ventral simple chaetae not seen. Aciculae tricuspid, 3 on anterior parapodia ( Fig. 74E), 2 on midbody parapodia ( Fig. 74F). Pharynx wide, though about 7–8 segments; pharyngeal tooth conical, located in front of middle of pharynx ( Fig. 74A). Proventricle through 7 segments, similar in size to pharynx, with about 28 muscle cell rows.

Remarks. Pionosyllis rousei n.sp. is characterized by having compound chaetae distinctly bidentate, with both teeth similar and well separated from each other. Pionosyllis serratisetosa (López, San Martín & Jiménez, 1997) , from southwestern Mediterranean has similar chaetae, but the teeth on the blades are not separated and are smaller, the blades have a different shape; long spiniger-like compound chaetae are absent, and the pharyngeal tooth is located near anterior margin of pharynx. Pionosyllis longocirrata (Saint- Joseph, 1887), from the eastern Atlantic and Mediterranean Sea, also has the pharyngeal tooth located more anteriorly than P. rousei , and the blades of compound chaetae either have a minute distal tooth or none (see San Martín, 2003, for more details). Pionosyllis templadoi ( San Martín, 1991) from Cuba has a similar body and the position of pharyngeal tooth is also similar. The blades of compound chaetae, however, have a small distal tooth and an elongated proximal tooth ( San Martín, 1991). Pionosyllis luquei ( San Martín, 1990) , also from Cuba, has similar compound chaetae, although not as strongly hooked, with well-developed teeth, but the dorsal cirri are shorter, and the pharyngeal tooth is located more posteriorly ( San Martín, 1990).

Habitat. Substrate unknown, recorded from 244 m depth.

Distribution. Tasman Sea (Elisabeth and Middleton Reef).

Etymology. This species is named after Dr Greg Rouse, an Australian Polychaetologist.