Megalomma

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 : 130-131

Megalomma sp. cf. M. kaikourense Knight-Jones, 1997

( Fig. 13A–D )

Megalomma kaikourense Knight-Jones, 1997: 320 –321, fig. 5.

Material examined. AM W.45166, MI QLD 2444 (3).

Description of material examined. Specimens measuring up to 26 mm long and 3 mm wide, with eight thoracic and numerous abdominal chaetigers. Specimens not studied alive. Preserved material pale, some with radioles slightly pigmented with brown or orange ( Fig. 13B–D ). Radiolar eyes black ( Fig. 13B ). Body is pale cream, without spots, except for red pygidial eyepots. Radiolar crown with semicircular lobes. Dorsal and ventral flanges absent. Basal membrane and radiolar flanges absent. Six to eight vacuolated cells supporting radioles in cross section, basally. Dorsalmost pair of radioles longer than the rest, each with a large subdistal compound eye almost surrounding the whole radiole ( Fig. 13B ). 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, forming very low dorsal pockets only in some specimens ( Fig. 13C versus 13D); large triangular ventral lappets separated by a midventral incision ( Fig. 13B ). Glandular ridge absent on anterior chaetigers. Thoracic ventral shields separated from adjacent neuropodial tori by a gap ( Fig. 13B ). First ventral shield with M-shaped anterior margin. Interramal eyespots absent. Collar chaetae elongate narrowly-hooded in two oblique rows. Following thoracic chaetigers with conical notopodia, with superior elongate narrowly-hooded and inferior broadly-hooded notochaetae (type B). Thoracic neuropodial uncini avicular, with several rows of small similar-sized teeth above main fang, well developed breast and medium-sized handle. Companion chaetae with asymmetrical hood, and dentate 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 shorte handle. Pygidium with a low rim around ventral anus; two red eyespots on each side. Tube mucous with sediment and medium-sized calcareous particles such as shell and coral fragments and foraminiferans.

Remarks. These specimens are characterised by the presence of single radiolar eyes on the dorsalmost pair of radioles, collar dorsal margins not fused to faecal groove but possessing incipient lateral pockets on some specimens, lack of a caruncle, thoracic ventral shields separated from neuropodial tori and broadly-hooded inferior thoracic chaetae (type B). With these features, the specimens belong to "Group 2A" (sensu Knight-Jones 1997) and "Group 2A2" (sensu Capa & Murray 2009), groups recovered as paraphyletic from cladistic analyses of the genus performed so far ( Capa & Murray 2009; Tovar-Hernández & Carrera-Parra 2011). The Lizard Island specimens share the same pigmentation pattern as the type material ( Knight-Jones 1997). The specimens described herein differ from those from New Zealand by their size, the ones from Lizard Island being more than twice the length of those in the original description. Other minor differences may be a consequence of size, such as the length of dorsal lappets. The specimens examined herein possess inferior thoracic chaetae slightly more elongated than those drawn by Knight-Jones (1997). It would be ideal to compare further material of similar size to confirm the presence of this species in Australian waters.

Habitat. Sand and seagrass, 24 m depth.

Type locality. Kaikoura, New Zealand.

Distribution. New Zealand, Australia (Queensland: Lizard Island).

Figures

FIGURE 13. A – D. Megalomma cf. kaikourense. A. Complete specimen, lateral view, with compound subdistal eyes in longest, dorsalmost radioles (one of the eyes is not fully developed, arrow); B. Anterior end, ventral view, with exposed radiolar eyes (arrows), thoracic ventral shields separated from neuropodial tori; C. Specimen with dorsal margins of collar separated, not fused to faecal groove but showing incipient pockets on both sides (arrow); D. Specimens without pockets; E – I. Megalomma sp. E-F, live specimen; E. Radiolar crown and thoracic chaetigers, lateral view; F. Detail of radiolar tips, with compound subdistal radiolar eyes present in most radioles (arrows); G. Thoracic and anterior abdominal chaetigers, ventral view, showing the wide gap between ventral shields and thoracic neuropodia; H. Detail of inferior thoracic notochaetae, broadly-hooded type B; I. Thoracic avicular uncini, with several rows of small teeth, all similar in size above main fang, well developed breast and medium-sized handle. Photographs: E, F by Alexander Semenov.