Gesaia, KIRTLEY, 1994

Capa, María, Hutchings, Pat & Peart, Rachael, 2012, Systematic revision of Sabellariidae (Polychaeta) and their relationships with other polychaetes using morphological and DNA sequence data, Zoological Journal of the Linnean Society 164 (2), pp. 245-284 : 259

GESAIA KIRTLEY, 1994

Gesaia Kirtley, 1994: 166 .

Type species: Phalacrostemma elegans Hartman & Fauchald, 1971: 152 (not Fauvel, 1911) designated by Kirtley (1994). Type locality: Bermuda rise, WHOI Chain Sta. 84, 36 °24.4′N, 67 °56′W; 4749 m.

Diagnosis: Monophyly of this genus has not been assessed but the species are characterized by: a long operculum divided into two lobes, with long opercular papillae, simple tentacular filaments, nuchal hooks with no limbations, branchiae on segment 2, median organ present, absence of nuchal flaps, and the presence of capillary chaetae in parathoracic neuropodia.

Description: Operculum longer than wide, completely divided into two free lobes and distal disc perpendicular to operculum; few (4–8 pairs) long and conical opercular papillae. Three to five simple (unbranched) tentacular filaments along margins of buccal cavity. Buccal flaps absent. Palps shorter or similar in length to operculum with obvious groove. Conspicuous median organ (cirrus) at dorsal junction of lobes. Outer paleae arranged in semicircles with straight, cylindrical, smooth blades (with ornamented thecae but no denticles). Inner opercular paleae arranged in a single row, like a straight line, on the dorsal half of the inner margin of lobes, with straight cylindrical and smooth paleae. One pair of nuchal spines with bent tips (hooks), without limbation. Neuropodia of segment 1 with two pairs of cirri (only described in type species) on both sides of building organ and without neurochaetae. Two lateral lobes in segment 2 (only described in type species). Thoracic branchiae present. Four pairs of parathoracic segments. Parathoracic neurochaetae only capillaries.

Remarks: The differences between Gesaia and other sabellariids were not clearly stated when this genus was erected ( Kirtley, 1994) and the monophyly of the genus and relationships with other sabellariids have not been assessed after phylogenetic analyses. Gesaia shares with Bathysabellaria , Mariansabellaria , Phalacrostemma , and Tetreres the occurrence of a long operculum with a perpendicular disc, long opercular papillae, and single tentacular filaments but only Gesaia , Mariansabellaria , and Phalacrostemma present an operculum with completely separated lobes. Gesaia , however, is unique among these taxa, based on the combination of the following features: presence of nuchal hooks with no limbations, branchiae on segment 2, conspicuous median organ, and absence of nuchal flaps. Gesaia currently contains eight species distinguished by the ornamentation of the thecae on the outer paleae. It has been reported from all the major oceans, occurring only in deep water ( Kirtley, 1994).