Megalomma acrophthalmos Grube 1878

Megalomma cf. acrophthalmos (Grube, 1878)

(Fig. 11 A–C)

Sabella acrophthalmos Grube, 1878: 258 –259.

Megalomma acrophthalmos.— Knight-Jones 1997: 316, fig 2A–L; Tovar-Hernández & Carrera-Parra 2011: 15 –17, fig 2A–L. Non Megalomma cf. acrophthalmos.— Capa & Murray 2009: 208, figs 4C–D, 5B, 6.

Material examined. AM W.44206, MI QLD 2370.

Description of material examined. Incomplete specimen; eight thoracic and numerous abdominal chaetigers. Live specimens not studied. Preserved specimens with a few reddish spots on the radiolar crown (Fig. 11 A), body without pigment, white. Radiolar crown with semicircular basal lobes. Dorsal and ventral basal flanges absent. Basal membrane absent. Radioles with smooth outer margins. Six to eight rows of vacuolated cells supporting radioles basally. Radiolar eyes apparently absent; two dorsal most radioles with unpigmented subdistal expansions. Dorsal lips with long radiolar appendages, one pair of pinnular appendages. Ventral lips and parallel lamellae present, ventral sacs absent. Caruncle present, rounded and with transverse rows of cilia. Posterior peristomial ring collar up to the base or radiolar crown, with dorsal margins fused to faecal groove, and forming two flanking spatulate dorsal flaps (Fig. 11 C); ventral lappets separated by a midventral incision (Fig. 11 B). Thoracic ventral shields separated from thoracic tori by a small gap (Fig. 11 B). Interramal eyes absent. Collar chaetae elongate, narrowly-hooded, in two oblique rows. Following thoracic chaetiger with conical notopodia; superior thoracic chaetae elongate narrowly-hooded; inferior broadly-hooded (type B). Thoracic uncini with several rows of similarsized teeth over main fang, covering slightly over half its length, with well developed breast and medium-sized handle. Companion chaetae with dentate appearance on proximal half of hood, distally asymmetrical. Abdominal neuropodia as low elevations with elongate, broadly-hooded chaetae arranged in rows. Notopodial abdominal uncini similar to the thoracic but with shorter handle. Pygidium not studied. Tube unknown.

Remarks. This specimen is characterised by having ventral shields separated from neuropodial tori by a narrow gap, long and slender inferior thoracic chaetae (type B), thoracic uncini with medium-length handles, a collar with dorsal margins fused to faecal groove, conspicuous and spatulate dorsal lappets, and a ciliated caruncle.

All these features agree with the recent description of Megalomma acrophthalmos (Grube, 1878) by Tovar- Hernández & Carrera-Parra (2011), except that M. acrophthalmos typically possesses subdistal compound eyes on most radioles, apparently absent in this specimen. Regeneration of the distal end of radioles is speculated, supported by the observation of enlarged knobby structures on both dorsalmost radioles. It is also different, however, to the specimens from Western Australia reported by Capa & Murray (2009) as M. cf. acrophthalmos, which have a short keel-like structure between the dorsal lips, unlike the ciliated caruncle present on this specimen and M. acrophthalmos. Thus we are tentatively assigning the specimen to M. acrophthalmos until more undamaged material is found. If this identification is confirmed it would represent the first record for the species in Australia. Megalomma acrophthalmos was grouped together with other species sharing the presence of a collar with dorsal margins fused to faecal groove, pockets present and eyes in most radioles, into "Group 1A" of Knight-Jones (1997) (Capa & Murray 2009), a group recovered as a monophyletic clade by Capa & Murray (2009) but not by Tovar- Hernández & Carrera-Parra (2011).

Habitat. Dead coral rubble, in shallow subtidal depths (6–9 m).

Type locality. Philippines.

Distribution. Philippines, Australia (Queensland: Lizard Island).