Megalomma
Creators: name: Capa, María
name: Murray, Anna
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Sabellida
Sabellidae
Megalomma

description: Megalomma sp.
(Fig. 13 E–I)
Material examined. AM W.44466, MI QLD 2424.
Description of material examined. Specimen incomplete, over 20 mm long and 3 mm wide. Seven thoracic and numerous abdominal chaetigers. Live specimen with radiolar crown with several orange and white transverse bands of different widths, especially conspicuous in inner margin of radioles and in pinnules (Fig. 13 E–F). Dorsalmost radiolar eyes orange, in some cases with a white reticule (Fig. 13 F), other smaller eyes brown (Fig. 13 F). Body is pale cream, with anterior end covered in white spots (Fig. 13 E). Specimens lose pigmentation after fixation, only a few pigmented bands stay on radioles, and are white with dark brown radiolar eyes. Radiolar crown with semicircular lobes (Fig. 13 E). Dorsal and ventral flanges absent. Basal membrane or radiolar flanges absent. About six vacuolated cells supporting radioles in cross section at the base. Dorsalmost pair of radioles longer than the rest, each with a large subdistal compound eye almost surrounding the whole radiole, all other radioles with smaller, spherical and similarly-sized subdistal eyes (Fig. 13 E–F). Dorsal lips with medium radiolar appendages, dorsal pinnular appendages absent. Caruncle absent. Ventral lips and parallel lamellae present, ventral sacs inside radiolar lobes. Posterior peristomial ring with margins separated by a wide gap, not fused to faecal groove, not forming dorsal pockets (Fig 13 E); triangular ventral lappets separated by a midventral incision (Fig. 13 G). Glandular ridge absent on anterior chaetigers. Thoracic ventral shields separated from adjacent neuropodial tori by a gap (Fig. 13 G). First ventral shield with M-shaped anterior margin (Fig. 13 G). Interramal eyespots absent. Collar chaetae elongate narrowly-hooded in two oblique rows. Following thoracic chaetigers with conical notopodia; superior elongate narrowly-hooded and inferior broadly-hooded notochaetae (type B, Fig. 13 H). Thoracic neuropodial uncini avicular, with several rows of small teeth, all similar in size above main fang, well developed breast and medium-sized handle (Fig. 13 I). 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 not observed.
Remarks. This specimen resembles M. interrupta, described above, in that the dorsal collar margins are not fused to the faecal groove and ventral shields are separated by a gap from adjacent neuropodial tori. However, unlike M. interrupta, it possesses distal eyes on all radioles, all spherical and similar in size, except for the dorsalmost pair, which are larger and surround the radiolar tip almost completely. According to artificial grouping of Megalomma species, this species belongs to ′′Group 2C′′ together with M. trioculatum Reish, 1968, described from Marshall Islands and Megalomma sp. 2 described from Victoria, Australia (Knight-Jones 1997; Capa & Murray 2009). Megalomma trioculatum is distinguished from the specimen described herein by the type of inferior thoracic chaetae, which have abruptly narrowing tips (type A), whereas in this specimen they are progressively tapering (type B) (Capa & Murray 2009). Megalomma sp. 2 also differs from this specimen as it only bears radiolar eyes on the two dorsalmost pairs of radioles instead of on all radioles (Capa & Murray 2009).
Habitat. Coral rubble, between 5–12 m depth.
Type locality. Lizard Island.
Distribution. Australia (Queensland: Lizard Island).
description: Published as part of Capa, María & Murray, Anna, 2015, A taxonomic guide to the fanworms (Sabellidae, Annelida) of Lizard Island, Great Barrier Reef, Australia, including new species and new records, pp. 98-167 in Zootaxa 4019 (1) on page 132, DOI: 10.11646/zootaxa.4019.1.8, http://zenodo.org/record/240803