Bathyditrupa Kupriyanova 1993

Genus Bathyditrupa Kupriyanova, 1993a

Bathyditrupa Kupriyanova 1993a: 21 –22.—ten Hove & Kupriyanova 2009: 29.—Kupriyanova et al. 2011: 2–3.

Type species: Bathyditrupa hovei Kupriyanova, 1993a

Diagnosis (after ten Hove & Kupriyanova 2009): Tube white, opaque, free-lying, curved but not coiled, rectangular in cross-section; peristomes absent. Operculum inverse conical, with flat or slightly concave brown chitinous endplate. Opercular ampulla gradually merges (constriction absent) into thick, rather triangular peduncle with pinnules, but without wings. Peduncle inserted as 2nd dorsal radiole on either side. Pseudoperculum absent. Up to six radioles per lobe in semi-circular arrangement. Radiolar eyes not observed. Inter-radiolar membrane and stylodes absent. Mouth palps not observed. 5 thoracic chaetigerous segments, 4 of which uncinigerous. Collar not divided into lobes (=unlobed), short, with straight edge. Tonguelets between ventral and lateral collar parts absent. Thoracic membranes short, ending at 2nd chaetiger. Collar chaetae limbate capillaries. Apomatus chaetae absent. Thoracic uncini saw-to-rasp-shaped, with up to 4 (6) teeth in a transverse row above anterior peg, with about 15 curved teeth in a row in profile view. Anterior peg flat gouged. Thoracic triangular depression absent. Abdominal chaetae all capillaries, posterior ones slightly longer. Abdominal uncini rasp-shaped. Achaetous anterior abdominal zone short, just one or two segments. Posterior glandular pad absent.

Remarks. Morphology of the animals (operculum, peduncle, and thoracic membranes), general appearance of tube wall (crystal size, orientation, structure), and the outer layer in tubes of Bathyditrupa hovei are similar to those of Spirodiscus grimaldii and S. groenlandicus comb. nov. (see below), thus suggesting a close relationship of Bathyditrupa to Spirodiscus. However, a significant difference between Spirodiscus and Bathyditrupa is the structure of abdominal chaetae that are typical flat geniculate in the former, but are very unusual, simple capillary in the latter. Because of this difference, we propose maintaining Bathyditrupa as a valid genus until new data contradicting this assumption become available.