Megalomma georgiense, Tovar-Hernández & Carrera-Parra, 2011

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 : 56-58

Megalomma georgiense n. sp.

Figure 26A–L

Type material. Holotype [ USNM] 61328 and one paratype [ USNM] 1140265, off Georgia, USA, 30° 57’ N, 79° 58’ W, May 17, 1977, Sta. 5H, Vessel Pierce R / V, 183 m.

Additional material examined. [ USNM] 061326, one topotype, off Georgia, 30° 57’ N, 79° 58’ W, August 30, 1977, Sta. 5H, Vessel Pierce R / V, 183 m. [ USNM] 061327, one topotype, off Georgia, 30° 57’ N, 79° 58’ W, February 27, 1977, Sta. 5H, Vessel Pierce R / V, 183 m.

Diagnosis. Eyes in most radioles (spherical); ventral radioles with ocular spots; dorsal collar margins not fused to faecal groove; anterior peristomial ring exposed dorsally; thoracic chaetae Type C; abdominal chaetae narrowly hooded.

Description. Branchial crown longer than thorax with 14 pairs of radioles (14). Outer surfaces of radioles quadrangular basally, rounded distally. Sub-distal compound eyes present in most radioles. Dorsalmost radioles with large spherical eyes, radiolar tips short ( Fig. 26E ). Other dorsal and lateral radioles with spherical eyes distinctly smaller than dorsalmost ones. Ventral radioles with ocular spots ( Fig. 26F–G ). Radiolar tips longer gradually towards ventral radioles ( Fig. 26F–G ). Dorsal collar margins diagonal, not fused to faecal groove ( Fig. 26A ). Dorsal lappets absent. Dorsal pockets absent ( Fig. 26A ). Ventral lappets with triangular anterior margins, not overlapping ( Fig. 26B–C ), slightly longer than ventral shield of collar. Anterior peristomial ring totally exposed dorsally ( Fig. 26A ). Lateral collar margins not covering bases of radioles. Dorsal lips erect, triangular, with mid-rib; dorsal pinnular appendages absent. Ventral lips about a half as long as dorsal lips, broadly rounded. Ventral sacs present. Caruncle absent. Keel absent. Body depressed, total thorax-abdomen length 28 mm (29–35), maximum width 2.5 mm (2) throughout most of thorax. Seven thoracic chaetigers. Thoracic tori longest on chaetigers 2–3, occupying a half of the distance between notopodia and ventral shield margins ( Fig. 26B–C ), not contacting shields. Notopodial fascicles with superior group of elongate, narrowly hooded chaetae ( Fig. 26I ); an inferior group chaetae Type C ( Fig. 26H ). Thoracic uncini with crest surmounted by 9–10 rows of numerous minute teeth, handles 2x length of main fang ( Fig. 26K ). Companion chaetae with teardrop-shaped membranes. Abdominal segments 78 (67–73). Tori slightly shorter than those on chaetiger 7. Abdominal chaetae narrowly hooded ( Fig. 26J ). Abdominal uncini with main fang surmounted by 8–10 rows of numerous minute teeth; handles reduced, less than half length of handles of thoracic uncini ( Fig. 26L ). Pygidium bilobed without eyespots. Tubes composed of shell fragments.

GAMETES: Paratype female with oocytes in abdomen.

Remarks. Megalomma georgiense n. sp., M. interrupta , M. trioculatum , M. kaikourense , M. pigmentum , M. gesae and M. bioculatum shares the presence of the dorsal collar margins not fused to the faecal groove. Megalomma georgiense n. sp., differs from M. interrupta by having ocular spots in ventral radioles (absent in M. interrupta ); compound eyes in most radioles (1–8 pairs of eyes, always in dorsalmost radioles and with a heterogeneous distribution in lateral radioles in M. interrupta ); dorsal pockets absent (low pockets in M. interrupta ) and anterior peristomial ring exposed totally dorsally (exposed dorsally only between the dorsal pockets in M. interrupta ). In M. georgiense n. sp., M. bioculatum and M. kaikourense the anterior peristomial ring is exposed totally dorsally. However, M. bioculatum and M. kaikourense have radiolar eyes only in the dorsalmost pair while the new species described here have eyes on most radioles.

Among the species from America, M. bioculatum , M. gesae , M. pigmentum and M. georgiense n. sp., have the dorsal collar margins not fused to faecal groove but in M. gesae and M. pigmentum basal ventral flanges are present (absent in M. bioculatum and M. georgiense n. sp.); M. pigmentum has a caruncle (absent in M. bioculatum , M. gesae and M. georgiense n. sp.); and M. bioculatum has eyes only in the dorsalmost radiolar pair while M. georgiense n. sp., has eyes in most radioles. Ocular spots are only present in M. circumspectum , M. pacifici and in M. georgiense n. sp., and these three species have eyes in most radioles; however, M. georgiense n. sp., is distinguishable by having the anterior peristomial ring exposed totally dorsally and dorsal collar margins not fused to faecal groove (not exposed and dorsal margins fused to faecal groove in M. pacifici and M. circumspectum ).

Etymology. The specific epithet refers to the collecting zone, off Georgia, USA.

Figures

FIGURE 26. Megalomma georgiense n. sp. A) Thorax, dorsal view; B–C) same, ventral views; D) dorsalmost radiolar eye; F) eye and spot of a lateral radiole; G) eye and spot of a ventral radiole; H) thoracic paleate chaetae; I) thoracic narrowly hooded chaetae; J) abdominal parapodium; K) thoracic uncini; L) abdominal uncini. A–B, D–L) Holotype from Georgia, USNM, 061328; C) paratype, USNM, 061328. Scale bars: A–C) 1 mm; D–F) 0.3 mm; H–L) 0.02 mm.