Megalomma interrupta

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, Zootaxa 4019 (1), pp. 98-167 : 126-128

Megalomma interrupta Capa & Murray, 2009

( Fig. 11 D–F)

Megalomma interrupta Capa & Murray, 2009: 210 –212, figs 2J–L, 4E–F, 5B, 7, 8.

Material examined. Queensland, Lizard Island: AM W.35859, North Point, 14°40′ S, 145°28′ E, coral block washings, 3.5 m, 4 Dec 1974; AM W.35490, off Station Beach, 14°41′S, 145°27′E, dead Pocillopora , 3 m, 6 Jan 1975; AM W.35491 (3, 1 on SEM), south headland of Turtle Beach, 14°39'S, 145°27'E, dead branching coral, 3 m, 27 Aug 1976; AM W.35492, off Granite Bluff, 14°39'S, 145°27'E, thin plates dead coral, 6 m, 31 Aug 1976; AM W.35493 (2), off Coconut Beach, 14°41' S, 145°28'27"E, dead coral covered in Lithothamnion , 12 m, 29 Mar 1995; AM W.35494, reef front between Bird and South Islands, 14°41′53′′S, 145°27′51′′E, dead coral, 13 m, 30 Mar 1995; AM W.35495, off North Point, 14°38′51′′S, 145°27′12′′E, dead coral with coralline algae, 20 m, 28 Mar 1995; AM W.36483 (2), Bird Islet, front reef, 14°41′48′′S, 145°27′51′′E, coarse coral rubble, 3 m, 8 Feb 2009; AM W.40857, lagoon, 14°40′S, 145°27′E, 1986; AM W.41101, 14°38′51′′S, 145°29′16′′E, 7–12 m, 3 Sep 2010; AM W.41102 (2), Lagoon between Palfrey Island and South Island, 14°41′51′′S, 145°27′01′′E, coarse coral rubble, 2 m, 1 Sep 2010; AM W.41108 (2), High Rock, 14°49′34′′S, 145°33′08′′E, coarse coral rubble, 6 m, 11 Sep 2010; AM W.41109 (2), North Direction Island, 14°44′43′′S, 145°30′18′′E, coarse coral rubble, 8 m, 26 Aug 2010; AM W.41112, Watsons Bay, 14°39′26′′S, 145°27′03′′E, coarse coral rubble, 4.5 m, 28 Aug 2010; AM W.41114, North Point, out from reef edge, 14°39′14′′S, 145°27′22′′E, coarse coral rubble, 5 m, 17 Apr 2008; AM W.41116, 14°41′00′′S, 145°26′29′′E, coral rubble, 2 m, 16 Apr 2008; AM W.47231, lagoon, 14°40′S, 145°27′E, 1986; AM W.47339, Coconut Beach, 14°40′53′′S, 145°28′21′′E, Halimeda algae and coral rubble, 2 m, 7 Feb 2009; AM W.44363, MI QLD 2359 (6); AM W.45164, MI QLD 2446; AM W.44215, MI QLD 2359 (8).

Description of material examined. Specimens up to 20 mm long and 5 mm wide with eight thoracic and numerous abdominal chaetigers. Live specimens with radiolar crown with several orange-brown and white transverse bands of different widths. Radiolar eyes orange-brown, in some cases with a white reticule. Body is pale orange, with anterior end covered in white spots ( Fig. 11 A–C). Collar has a white margin, more conspicuous dorsally and possesses orange spots along the ventral edge of neuropodial tori ( Fig. 11 F). Preserved specimens lose the white bands on radiolar crown and only the brown ones remain. The white spots on body also fade and the thoracic ventral spots on tori turn brown. Radiolar crown with semicircular lobes. Dorsal and ventral flanges absent. Basal membrane or radiolar flanges absent. About 10 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 ( Fig. 11 D–E), and with visible ommatidia. Next adjacent 4–5 pairs of radioles without eyes, and two pairs of lateral radioles with small, similarly-sized subdistal eyes. Dorsal lips with medium radiolar appendages, and a pair of dorsal pinnular appendages. Caruncle absent. Ventral lips and parallel lamellae present, ventral sacs inside radiolar lobes. Posterior peristomial ring collar not fused to faecal groove, with dorsolateral indentations on both sides forming inconspicuous pockets and continuing as ridges to the middorsal faecal groove ( Fig. 11 E); pointed ventral lappets separated by a midventral incision ( Fig. 11 F). Glandular ridge absent on anterior chaetigers. Thoracic ventral shields separated from adjacent neuropodial tori by a gap ( Fig. 11 F). First ventral shield with m-shaped anterior margin. Interramal eyespots absent. Collar chaetae elongate narrowlyhooded in two oblique rows. Following thoracic chaetigers with conical notopodia; with superior elongate narrowly-hooded and inferior broadly-hooded notochaetae (type A). Thoracic neuropodial uncini avicular, with several rows of small similar-sized teeth above main fang, well developed breast and long handle. Companion chaetae with asymmetrical hood, fibrous appearance on proximal half of hood. Abdominal neuropodia as low elevations with elongate, broadly-hooded chaetae arranged in rows. Notopodial abdominal uncini similar to thoracic uncini but with shorter handles. Pygidium as a rounded papilla without pygidial eyes. Pygidial cirrus absent. Tube membranous with large sediment particles (broken shells, coral fragment, foraminiferans, etc.) attached to exposed end ( Fig. 11 D).

Remarks. This species is characterized by having inconspicuous dorsal collar pockets, radiolar eyes present in dorsalmost and lateral radioles, with approximately four radioles in between without eyes, radiolar skeleton with approximately 10 cells in cross section, caruncle absent, and inferior thoracic broadly-hooded of type A ( Capa & Murray 2009). All other congeners bear radiolar eyes on one or several radioles, and no other species has yet been described in the genus with eyeless intermediate radioles flanked by dorsal and lateral ones bearing compound distal eyes. Megalomma interrupta was allocated by Capa & Murray (2009) to a subgroup of Knight-Jones "Group 2" (1997) due to having collar margins not fused to faecal groove. However, in both cladistic analyses performed to date, this group has been recovered as paraphyletic ( Capa & Murray 2009; Tovar-Hernández & Carrera-Parra 2011).

Habitat. Dead coral and coral rubble, 2– 20 m.

Type locality. One Tree Island, Queensland.

Distribution. Indonesia (Pasir Sari), Australia (Queensland, tropical Western Australia).

Figures

FIGURE 11. Megalomma sp. cf. M. acrophthalmos. A. Detached radiolar crown, base at bottom of the photograph; B. Thoracic and anterior abdominal chaetigers, ventral view; showing thoracic ventral shields separated from neuropodial tori; C. Dorsal collar margins, with spatulate flaps and medial caruncle; D – F. Megalomma interrupta, live specimens; D. Specimen inside its tube, with exposed radiolar crown, dorsalmost pair of compound radiolar eyes stick out vertically; E. Anterior end, dorsal view, with subdistal compound radiolar eyes present (arrows) or absent circles; F. Thoracic and anterior abdominal chaetigers; showing enlarged collar ventral lappets and thoracic ventral shield separated from neuropodial tori. Photographs: D – F by Alexander Semenov.