Megalomma jubata, Capa, María & Murray, Anna, 2015

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 : 128-130

Megalomma jubata n. sp.

( Fig. 12 )

Material examined. Queensland, Lizard Island: Holotype, AM W.36495, MacGillivray Reef, 14°39'25"S, 145°29′41′′E, coarse coral rubble, 2 m, 21 Feb 2009. Paratypes, AM W.36480 (2), Linnet Reef, Great Barrier Reef, 14°46′50′′S, 145°20′58′′E, coarse coral rubble, 4 m, 23 Feb 2009; AM W.36481, Coconut Beach, 14°40′53′′S, 145°28′21′′E, Halimeda algae & coral rubble, 2 m, 7 Feb 2009; AM W.41106; AM W.47337, 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.47338, Watsons Bay, 14°39′26′′S, 145°27′03′′E, coarse coral rubble, 4.5 m, 28 Aug 2010.

Other material examined. Queensland, Heron Island: AM W.39514.001 (on SEM), Sykes Reef, 23°25′56′′S, 152°02′02′′E, 15 m, 14 Nov 2009.

Description. Holotype a complete specimen, 23 mm long (crown of 5 mm) and 2.5 mm wide, with seven thoracic chaetigers and numerous abdominal segments; paratypes up to 25 mm long (crown 5 mm), 2.5 mm wide; thorax with 6–11 chaetigers, numerous abdominal chaetigers. Specimens not observed alive. Some preserved specimens with longitudinal bands of pigment on radiolar bases, and three or four faint brown and orange transverse bands of pigment in radioles and pinnules ( Fig. 12 A–B). The caruncle may also have faint pigment distally. Some specimens pigmented dorsally and ventrally on thorax and collar, with darker pigment patches ventral to neuropodial tori and between neuro- and notopodia. Radiolar crown with semicircular lobes ( Fig. 12 A– B). Dorsal and ventral flanges absent. Basal membrane or radiolar flanges absent. About 10 vacuolated cells supporting radioles in cross section basally. Dorsalmost pair of radioles longer than the rest, each with a large subdistal compound eye spiralling around radiolar tip; additional pair of eyes on following two dorsalmost radioles, decreasing in size. Dorsal lips with medium-length radiolar appendages ( Fig. 12 F), three pairs of dorsal pinnular appendages. Caruncle present ( Fig. 12 C–E, G). Ventral lips and parallel lamellae present, ventral sacs present ( Fig. 12 D). Posterior peristomial ring collar with dorsal margins fused to faecal groove and forming dorsal pockets at either side and short, rounded dorsal lappets ( Fig. 12 E); midventral incision separating low ventral lappets ( Fig. 12 D). Glandular ridge on anterior chaetigers absent. Thoracic ventral shields separated from adjacent neuropodial tori by a gap ( Fig. 12 C–D). 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, Fig. 12 H–I). Thoracic neuropodial uncini avicular, with several rows of small similar-sized teeth above main fang ( Fig. 12 J), well developed breast and medium-sized handle. Companion chaetae with dentate appearance on proximal half of hood, distally asymmetrical ( Fig. 12 J). Abdominal neuropodia as low elevations with elongate, broadly-hooded chaetae arranged in rows ( Fig. 12 K). Notopodial abdominal uncini similar to thoracic uncini but with shorter handles ( Fig. 12 L). Pygidium rounded with scattered eyespots. Pygidial cirrus absent. Tube membranous and embedded with sand, crushed coral fragments and other small debris.

Variation. Paratypes have 0–5 pairs of compound distal eyes on dorsalmost radioles.

Remarks. Megalomma jubata n. sp. is characterised by the presence of a conspicuous caruncle, dorsal collar margins fused to faecal groove forming pockets at either side and with short rounded dorsal lappets, radiolar eyes on 1–5 pairs of dorsalmost radioles, thoracic neuropodial tori separated from ventral shields and inferior thoracic chaetae type B. It would therefore be allocated to the informal "Group 1C" (proposed by Capa & Murray 2009) together with M. quadrioculatum ( Willey, 1905) , that also bears a caruncle. Megalomma jubata n. sp. differs from M. quadrioculatum in the shape of the inferior thoracic chaetae, which are type B, compared with type A in M. quadrioculatum . Other congeners described as having a caruncle, a homoplastic feature ( Capa & Murray 2009; Tovar-Hernández & Carrera-Parra 2011) are M. carunculata Tovar-Hernández & Salazar-Vallejo, 2008 , M.

lobiferum ( Ehlers, 1887) , M. pigmentum Reish, 1963 , and M. suspiciens ( Ehlers, 1904) . Megalomma pigmentum possesses widely separated dorsal collar margins, lacks collar pockets on either side, and bears a single pair of radiolar eyes. Megalomma suspiciens , M. carunculata and M. lobiferum which all have a similar collar morphology to the new species, bear compound eyes in most of the radioles instead of only in a few of the dorsalmost.

The external morphology of the caruncle of this species is remarkable in comparison with other described Megalomma possessing this structure. The cilia are arranged in four parallel transverse ridges joined anteriorly by an additional longitudinal ridge. It resembles, at least superficially, the nuchal organs present in some members of Amphinomidae , a group of annelids not closely related, but with ciliary ridges also located in the along caruncle (see also Tovar-Hernández & Salazar-Vallejo 2008). The function(s) of this structure is unknown, but most probably sensory ( Tovar-Hernández & Salazar-Vallejo 2008). Of the other species of Megalomma provided with a caruncle, M. lobiferum has been shown to have cilia arranged in four longitudinal rows on each anterior posterior and lateral sides of this triangular structure. By contrast, the caruncle of M. jubata n. sp. is rounded and bears cilia in a different arrangement.

Etymology. The species name is derived from the Latin word “iuba”, alluding to the characteristic rounded crest herein referred to as a caruncle, located dorsally to the mouth, between the dorsal lips.

Habitat. Coral rubble, with sand and Halimeda algae, in shallow intertidal to subtidal depths.

Type locality. Lizard Island.

Distribution. Australia (Queensland: Lizard and Heron Islands).

Figures

FIGURE 12. Megalomma jubata n. sp. A – C, preserved specimens; A. Detached radiolar crown showing pigmentation pattern; B. Half of the radiolar crown, from inside, showing the medium length radiolar appendages (arrow); C. Thorax and anterior abdominal chaetigers, radiolar crown detached leaving an exposed caruncle (arrow); D – L. Scanning electron micrographs; D. Anterior thoracic chaetigers showing the morphology of collar and the exposed caruncle at the back; E. Anterior chaetigers showing collar dorsal margins fused to faecal groove and with pockets at both sides, and a middorsal prostomial caruncle; F. Detail of dorsal lips and radiolar appendages; G. Detail of the rounded caruncle, with four parallel transverse ridges of cilia, anteriorly joined by a longitudinal row of cilia; H. Thoracic notochaetae, superior narrowly-hooded and inferior broadlyhooded type B; I. Detail of broadly-hooded inferior thoracic chaetae; J. Thoracic uncini with several rows of small teeth, all similar in size above main fang; companion chaetae with asymmetrical fibrous hood; K. Abdominal chaetae narrowly-hooded. L. Abdominal uncini with several rows of small teeth, all similar in size above main fang.