Stylomma palmatum Quatrefages 1866

Stylomma palmatum (Quatrefages, 1866)

(Fig. 22 G–J)

Sabella palmata Quatrefages, 1866: 453.

Sabella monophthalma Augener, 1922: 35.

Stylomma palmatum.— Knight-Jones 1997: 322; Knight-Jones & Perkins 1998: 451 –452, figs. 29, 31A–B; Capa 2008: 321 – 324, figs 10A–D, 11.

Material examined. Queensland, Lizard Island: AM W.41156, AM W.36455, AM W.36456, Watsons Bay, 14°39′26′′S, 145°27′03′′E, coral rubble, 4.5 m, 28 Aug 2010.

Other material examined. Queensland, Heron Island: AM W.41154, AM W.41155, lagoon, 23°26′30′′S, 151°54′02′′E, coral rubble, 1–15 m, 19 Nov 2010.

Description of material examined. Largest complete specimen 43 mm long (including crown of 13 mm length), 2.5 mm wide, with 8 thoracic and>100 abdominal chaetigers. Live specimens are mainly white, with the base of the radiolar crown bright white with conspicuous brown markings. Radioles have longitudinal dark lines basally, and transverse bands on radioles and pinnules on the distal 2/3rds of their length (Fig. 22 G–H, J). Body without colour pigment. (Fig. 22 G, I). Interramal eyespots are present in both thorax and abdomen. Preserved specimens maintain same pigmentation pattern. Radiolar crown rigid, with long semicircular basal lobes, with rounded and long dorsal basal flanges joined dorsally with a “press-stud” structure (Fig. 22 G, J). Radioles with smooth radiolar flanges, broader distally; basal membrane present. Distal compound radiolar eye on each radiole, over a stalk, all similar in size. Numerous small vacuolated cells (over 20) support each radiole basally, with other smaller ones extending into and supporting flanges at the distal end. Dorsal lips with long pointed radiolar appendage; pinnular appendages absent. Ventral lips and parallel lamellae present, ventral sacs inside crown. Posterior peristomial ring collar with dorsal margins separated by a wide gap, oblique lateral margins increasing in length ventrally, ventral lappets separated by a midventral incision (Fig. 22 G, I). Glandular ridge on anterior chaetigers absent. Thoracic ventral shields in contact with neuropodial tori, or separated by a small gap (Fig. 22 I). Collar chaetae arranged in two short oblique rows, superior row with elongate narrowly-hooded chaetae and inferior row with spine-like chaetae. Thoracic notopodia conical, with chaetae arranged in longitudinal bundles; superior thoracic chaetae elongate narrowly-hooded, inferior spine-like. Thoracic uncini with over 10 rows of minute teeth above main fang, covering half its length. Companion chaetae with dentate appearance on proximal half of hood, distally asymmetrical. Abdominal neuropodia conical, lacking superior abdominal chaetae, inferior abdominal chaetae spine-like, arranged in a C-shaped to a spiral arrangement. Abdominal uncini similar to thoracic, but with slightly larger teeth above main fang. Pygidium a raised lobed rim with some lateral patches of pigment. Pygidial eyes and pygidial cirrus absent. Tube not studied.

Remarks. This species is easily distinguished from any other sabellid by the presence of single distal stalked eyes on all radioles, autapomorphy of the species. Moreover, it also has a distinctive pigmentation pattern as well as a robust and rigid radiolar crown with the two lobes joined by a press-stud structure. First record for Lizard Island.

Habitat. Dead coral and coral rubble.

Type locality. Kilinailau Islands, Micronesia.

Distribution. French Polynesia, Papua New Guinea, Queensland (Cape York, Lizard Island).