Megalomma gesae Knight-Jones, 1997

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 : 33-35

Megalomma gesae Knight-Jones, 1997

Figures 12A–E, 13A–E

Megalomma gesae Knight-Jones, 1997: 318–319 , Fig. 3, new name for Potamilla bioculata Hartmann-Schröder, 1959: 175– 176 , Figs 183–188.

Type material examined. [ ZMH] P–15246, holotype complete; P–15245, 18 paratypes (1 specimen of Chone removed to another vial), Estero Jaltepeque, La Herradura, El Salvador , 31.4–25.7 ‰, 27–30° C.

Additional material examined. [ ECOSUR] Panama, Balboa , Club de Yates, Coll. SISV, June 01, 2002 (20 specs) .

Diagnosis. Eyes only in dorsalmost pair of radioles (spherical); branchial crown with basal ventral flanges; dorsal margins of collar not fused to faecal groove; anterior peristomial ring exposed dorsal and laterally; keel present; thoracic chaetae Type C; abdominal chaetae broadly hooded.

Description. Branchial crown shorter than thorax with three pairs of radioles (3–6; 10–12). Base of branchial crown with ventral flanges ( Fig. 13W). Radioles with a purple or brown band, distributed over outer and lateral radiole margins and adjacent pinnules, the band occupies a space of 10 pairs of pinnules. Outer surfaces of radioles rounded. Sub-distal compound eyes present only in dorsalmost pair of radioles, spherical covering radiolar tips ( Figs 12D, 13E). All radiolar tips short. Dorsal collar margins diagonal, not fused to faecal groove ( Figs 12A–B, 13B). Dorsal lappets absent. Dorsal pockets absent ( Figs 12A–B, 13B). Ventral lappets prominent, longer than ventral shield of collar, triangular, not overlapped ( Figs 12C, 13C). Anterior peristomial ring exposed dorsal and laterally beyond collar margins ( Figs 12A–B, 13A–B, D). Lateral collar margins not covering basal union of radioles ( Figs 12B, 13A, D). Dorsal lips erect, triangular, about ¼ of branchial crown length, with mid-rib. Dorsal pinnular appendages present. Ventral lips broadly rounded. Ventral sacs present, in some specimens full of sand ( Figs 12C, 13C). Caruncle absent. Keel present ( Fig. 12A). Body pale to brown colored. Total thorax-abdomen length 3 mm (1.5– 3 mm; 13–31), maximum width 0.25 mm (0.20–0.25; 1.5–2) throughout most of thorax. Seven thoracic chaetigers (6–8). Thoracic tori of equal length in all segments. Tori in chaetigers 2–3 short, occupying a half of the distance between notopodia and ventral shields margins ( Fig. 12C), not contacting shields. Inferior thoracic chaetae Type C. Thoracic uncini with main fang surmounted by six rows of numerous minute teeth, handles 1.5x length of main fang. Companion chaetae with teardrop-shaped membranes. Abdominal segments 18 (42–52). Abdominal chaetae broadly hooded. Abdominal uncini with main fang surmounted by 8–10 rows of numerous minute teeth. Triangular posterior margin of pygidium without eyespots ( Fig. 12E). Tubes fine sand, smooth.

Remarks. Megalomma pigmentum and M. gesae are unique in the genus by having the ventral flanges located at the base of branchial crown. Both species also share the presence of the anterior peristomial ring exposed dorsally and laterally beyond collar, and spherical radiolar eyes only in dorsalmost radiolar pair, but M. gesae does not have a caruncle (present in M. pigmentum ), the branchial crown is shorter than thorax (longer than thorax in M. pigmentum ), all radioles with short tips (dorsalmost radioles with short tips increasing gradually towards ventral radioles in M. pigmentum ) and the ventral lappets are longer than the ventral shield of collar (as long as the ventral shield of collar in M. pigmentum ).