Megalomma sp. 2

Capa, María & Murray, Anna, 2009, Review of the Genus Megalomma (Polychaeta: Sabellidae) in Australia with Description of Three New Species, New Records and Notes on Certain Features with Phylogenetic Implications, Records of the Australian Museum 61 (2), pp. 201-224 : 220-221

Megalomma sp. 2

Fig. 12

Material examined. Victoria. MV F70842 (1spec. on SEM stub AM500 ) , eastern Bass Strait, 8.6 km west southwest of Cape Conran , 37°51'11"S 148°38'32"E .

Description. Single specimen incomplete, with eight thoracic chaetigers and five abdominal chaetigers. Crown with ten pairs of radioles, arranged in semicircles. External margins of radioles quadrangular, without lateral flanges ( Fig. 12A,B ). Tips of radioles shorter than pinnules. Subdistal eyes present on the two dorsalmost pairs of radioles; dorsalmost pair larger and almost surrounding the radiolar tip ( Fig. 12C ). Ventral lips rounded and well developed; ventral parallel lamellae and ventral sacs present. Dorsal margins of collar not fused to the faecal groove, terminating dorsolaterally and leaving a wide gap between them ( Fig. 12A,B ); collar pockets absent; lateral margins smooth, oblique; elongate, triangular, non-overlapping ventral lappets, with a complete midventral incision. Ventral shields quadrangular, similar in length along thoracic chaetigers, almost in contact with tori. First ventral shield with a straight anterior margin. First chaetiger with superior and inferior elongate narrowly hooded notochaetae; superior row longer than the inferior ( Fig. 12D ). Rest of thoracic chaetigers with superior elongate narrowly hooded notochaetae and inferior broadly hooded notochaetae with tips decreasing in width progressively, arranged in two rows ( Fig. 12G ). Thoracic uncini with several rows of small teeth, all similar in size, above main fang ( Fig. 12E ), uncinus with well developed breast. Companion chaetae with asymmetrical membrane and small teeth covering most of surface but with smooth distal tip ( Fig. 12F ). Abdominal neuropodia with broadly hooded chaetae ( Fig. 12I ). Abdominal uncini similar to thoracic ( Fig. 12H ) but with shorter handles. Pygidium missing.

Remarks. Megalomma sp. 2 resembles most closely M. cf. miyukiae specimens described herein, in the development of the collar (with dorsal collar margins separated from the faecal groove), in the presence of radiolar eyes in the dorsalmost radioles, and in the absence of a caruncle, but these two species are distinguished by the shape of the collar margins, which end abruptly in Megalomma sp. 2 , and form concave ends with low pockets in M. cf. miyukiae . Moreover ventral shields are separated from tori in this specimen, whereas these abut in M. cf. miyukiae .

Figures

Figure 12. SEM of Megalomma sp. 2, MV F70842. (A) anterior thoracic chaetiger and posterior peristomial ring collar, dorsal view; (B) same, lateral view; (C) dorsal most subdistal radiolar eye; (D) notochaetae, first chaetiger; (E) uncini, anterior thoracic chaetiger; (F) companion chaetae, anterior thoracic chaetae; (G) posterior thoracic notochaetal fascicle, ventral view; (H) anterior abdominal uncini; (I) anterior abdominal neurochaetal fascicle.