Megalomma sp.

Tovar-Hernández, María Ana & Carrera-Parra, Luis F., 2011, Megalomma Johansson, 1925 (Polychaeta: Sabellidae) from America and other world-wide localities, and phylogenetic relationships within the genus 2861, Zootaxa 2861 (1), pp. 1-71 : 58-59

Megalomma sp.

Figure 27A–F

Material examined. [ USNM] 33142, Acc. 261883, New Zealand, Auckland, Coll. Sewlyn J. Whitley (1 spec.). [ USNM] Acc. 300653, Otago Peninsula, Aquarium point, NW Riser Coll., from Macrocystis holdfast, March 14, 1983 (1 spec.) .

Diagnosis. Eyes in most radioles (spherical); dorsal margins of collar fused to faecal groove; dorsal lappets and dorsal pockets present; caruncle present; thoracic chaetae type B; abdominal chaetae narrowly hooded.

Description. Branchial crown shorter than thorax with 22–24 pairs of radioles. Outer surfaces of radioles quadrangular basally, rounded distally. Sub-distal compound eyes present in most radioles. Dorsalmost pair of radioles longer than others, rigid, rachis notably thick in lateral view, eyes distinctly larger, spherical (aFig. 27D). Second to lateral and ventral pairs of radioles with spherical eyes distinctly smaller than dorsalmost ones. All radiolar tips long ( Fig. 27E–F ). Dorsal collar margins rounded anteriorly, fused to faecal groove ( Fig. 27A ). Dorsal lappets rounded, reaching bases of dorsal radioles ( Fig. 27A ). Dorsal pockets well developed, U-shaped ( Fig. 27A ). Ventral lappets with short rounded anterior margins, not overlapping ( Fig. 27B ). Anterior peristomial ring not exposed beyond collar. Lateral collar margins not covering the basal union of radioles. Dorsal lips erect, triangular, very long, with mid-rib. Dorsal pinnular appendages unknown. Ventral lips about a half as long as dorsal lips, broadly rounded. Ventral sacs present. Caruncle as long as dorsal lappets, placed above the mouth, between dorsal lips, erect, triangular with rough base and smooth distal end. Keel absent. Total thorax-abdomen length 104–108 mm, maximum width 4–5 mm throughout most of thorax. Seven thoracic chaetigers. Thoracic tori of same length along thorax. Tori in chaetigers 2–3 occupy the entire distance between notopodia and ventral shield margins ( Fig. 27B ), contacting shields. Thoracic fascicles ( Fig. 27C ) with superior group of elongate, narrowly hooded chaetae; an inferior group of chaetae Type B ( Fig. 27Q ). Thoracic uncini with crest surmounted by 7–9 rows of numerous minute teeth, handles 2x length of main fang. Companion chaetae with teardrop-shaped membranes. Abdominal chaetae narrowly hooded. Abdominal uncini with main fang surmounted by 8–10 rows of numerous minute teeth. Pygidium rounded.

Remarks. Megalomma sp. , M. cinctum , M. gesae and M. multioculatum have branchial crown shorter than thorax. Among these species, M. gesae has dorsal collar margins not fused to the faecal groove (fused in the other three species). Megalomma cinctum has glandular ridges on chaetigers 2 and 3 (absent in M. suspiciens and M. multioculatum ). The eyes in dorsalmost radiolar pairs in M. multioculatum are spherical, the radiolar tips are short in dorsalmost radioles increasing gradually towards ventral radioles, the anterior peristomial ring is exposed dorsally between dorsal pockets and it is without a caruncle (dorsalmost eyes are spherical, all radioles have long tips and a caruncle is present in M. sp.).

Figures

FIGURE 27. Megalomma sp. A) Collar dorsal view; B) collar, ventral view; C) thoracic chaetigers; D) dorsalmost radiolar eye; E) eye from a lateral radiole; F) eye from a ventral radiole. A–F) Specimen from New Zealand, USNM, 300653. Scale bars: A–B) 1 mm; C) 0.5 mm; D–F) 0.3 mm.