Megalomma cf. acrophthalmos ( Grube, 1878 )

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 : 208-210

publication ID	https://doi.org/ 10.3853/j.0067-1975.61.2009.1529
persistent identifier	https://treatment.plazi.org/id/2202BF4F-FFCB-5B76-FCAB-57F3FDA8FC8D
treatment provided by	Felipe
scientific name	Megalomma cf. acrophthalmos ( Grube, 1878 )
status

Treatment

Megalomma cf. acrophthalmos ( Grube, 1878) View in CoL

Figs 4C–D View Figure 4 , 5B View Figure 5 , 6 View Figure 6

Sabella acrophthalmos Grube, 1878 View in CoL : page 258, 259. Megalomma acrophthalmos Knight-Jones, 1997: 316 View in CoL fig. 2.

Material examined. Western Australia. AM W35477, (1 spec.), Stn WA 621, north west of West Lewis Island , Dampier Archipelago, 20°33'31"S 116°38'13"E, intertidal, coll. P.Hutchings, 26 Jul.2000 GoogleMaps . MAGNT W14008, Roebuck Bay, Broome , 19°04'00"S 122°16'59"E, coll GoogleMaps . R. J. Hanley and M. Jebb, 29 Aug. 1991 (1 spec. on SEM stub, AM 499 ) .

(A) thoracic uncinus; (B) abdominal uncinus. Megalomma cf. acrophthalmos : (C) thoracic uncinus; (D) abdominal uncinus. Megalomma interrupta n.sp.: (E) thoracic uncinus; (F)

abdominal uncinus. Megalomma inflata n.sp.: (G) thoracic uncinus; (H) abdominal uncinus.

Megalomma sp. 1 : (I) thoracic uncinus; (J) abdominal uncinus. Megalomma suspiciens : (K)

thoracic uncinus; (L) abdominal uncinus. Scale: 0.1 mm.

Description. Largest specimen AM W35477, 30 mm long, 4 mm wide with eight thoracic and 108 abdominal chaetigers (smallest has eight thoracic and 53 abdominal chaetigers). Crown longer than thorax, 9 mm long, with 25 pairs radioles (15 pairs in the small specimen). Outer surface of radioles quadrangular at the base ( Fig. 6B View Figure 6 ) and rounded distally, with tips shorter than pinnules. Radiolar skeleton composed of 15–20 cells in transverse section ( Fig. 5B View Figure 5 ). Most radioles with subdistal eyes, dorsalmost four pairs appear spiral, and lateral ones large and becoming smaller more ventrally, lacking or missing in 1–2 pairs ventralmost radioles. Dorsal lips with radiolar appendages as long as two thoracic chaetigers, pinnular appendages absent. Caruncle absent. Low smooth keel (thickened and non-lamellate) projecting ventrally between dorsal lips, arising from raised triangular mound situated mid dorsal to dorsal lips. Ventral lips rounded and well developed; ventral parallel lamellae and sacs present. Posterior peristomial collar fused mediodorsally to the faecal groove; dorsal lappets present, elongate and spatulate-shaped distally, as long as lateral collar margins, and with dorsolateral U-shaped indentations on both sides forming pockets, reaching to level of second chaetiger ( Fig. 6A View Figure 6 ); lateral collar margins smooth ( Fig. 6B View Figure 6 ), and ventrally forming overlapping lappets with rounded anterior margins, with a complete midventral incision ( Fig. 6C View Figure 6 ). Ventral shields rectangular, all separate from the neuropodial tori ( Fig. 6C View Figure 6 ), all similar in width. First ventral shield longer than the rest, with m-shaped anterior margin. First chaetiger with superior and inferior elongate narrowly hooded notochaetae; superior longer than inferior ( Fig. 6D View Figure 6 ). Rest of thoracic chaetigers with two rows of superior elongate narrowly hooded and two rows of inferior broadly hooded notochaetae with progressively tapering tips (type B) ( Fig. 6E View Figure 6 ); lamella-like lobe present between superior and inferior notochaetal fascicles. Uncini with around 7–10 rows of small, similarly sized teeth above main fang ( Fig. 6F,G View Figure 6 ), well developed breast, handle long, three times the length of the distance from breast to main fang ( Fig. 4C View Figure 4 ). Companion chaetae with asymmetrical membrane ( Fig. 6H View Figure 6 ). Abdominal neuropodia with slender broadly hooded chaetae ( Fig. 6I View Figure 6 ). Abdominal uncini similar to thoracic uncini, with similarly-sized teeth over the main fang but covering more surface area ( Fig. 6J View Figure 6 ) and with shorter handle ( Fig. 4D View Figure 4 ). Pygidium with four small lobes, scattered eyespots laterally.

Colour pattern. Three regular transverse pigment bands on branchial radioles plus other less regular pigment on pinnules distally. Brown pigment present on anterior dorsum of body and with dark regular patches dorsolaterally on anterior margins of first seven thoracic segments.

Remarks. Of the species recorded in the Indo-Pacific, these described specimens most closely resemble M. multioculatum and M. phyllisae n.sp. in the presence of subdistal eyes on most radioles and with dorsal margins of collar fused to the faecal groove. However, M. cf. acrophthalmos has conspicuous elongated dorsal collar lappets which are absent in M. multioculatum and M. phyllisae n.sp. These three features (pattern of distribution of radiolar eyes, fusion and shape of collar dorsal margins), are shared with the type material described from the Philippines ( Grube 1878) and restudied and drawn by Knight-Jones (1997). The chaetae and uncini of specimens from both localities also show similarities: the inferior thoracic chaetae are broadly hooded but with a progressively-tapering hood (type B) and the thoracic uncini have long handles, exceeding twice the distance of main fang to breast. The only specimen available from the type locality (most probably the holotype according to Knight-Jones [1997]) is not in good condition. Because of this reason, identification should be confirmed with additional material from the type locality. However, it is quite possible that the species has a southeast Asian distribution. This species has also been recorded in Sri Lanka ( Willey, 1905) as Branchiomma acrophthalmos but this identification has not been confirmed.

Other species in the genus described as possessing well developed dorsal lappets are M. fauchaldi ( Giangrande et al., 2007) from Belize, M. vesiculosum from England, and M. mushaense and M. nechamae from the Red Sea, all of which also possess radiolar eyes on most radioles, collar fused to the faecal groove and pockets present, although this last feature was not interpreted as such by Knight- Jones (1997). The shape and size of the lappets and the margin of the collar of M. acrophthalmos are all different in shape and size to these four species, and their geographical distributions are discrete and separated widely enough to also separate them as different species.