Bathyditrupa Kupriyanova, 1993b

Kupriyanova, Elena K., Bailey-Brock, Julie & Nishi, Eijiroh, 2011, New records of Serpulidae (Annelida, Polychaeta) collected by R / V " Vityaz " from bathyal and abyssal depths of the Pacific Ocean, Zootaxa 2871, pp. 43-60 : 44-45

Bathyditrupa Kupriyanova, 1993b

Type-species: Bathyditrupa hovei Kupriyanova, 1993b

Generic diagnosis (after ten Hove & Kupriyanova 2009). Tube free, curved but not coiled, white, opaque rectangular in cross-section; collar-like rings absent. Granular overlay 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. Branchial eyes not observed. Inter-radiolar membrane and stylodes absent. Mouth palps not observed. Five thoracic chaetigerous segments, four of which uncinigerous. Collar not divided into lobes (=unlobed), short, with straight edge. Tonguelets absent. Thoracic membranes short, ending at 2nd chaetiger. Collar chaetae limbate capillaries. Apomatus chaetae absent. Thoracic uncini saw-to-rasp-shaped, with up to four (?six) teeth in a transverse row above anterior peg, with about 15 curved teeth in a row in profile view. Anterior peg 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. The most characteristic feature of the genus is a free, unattached tube similar to that of Ditrupa , but rectangular in cross-section and without an outer hyaline layer. Other distinctive characters include the short thorax with only five thoracic chaetigers and the operculum borne on thick pinnulate peduncle. Jäger (2004) synonymised the extant monotypic genus Spirodiscus Fauvel, 1909 characterized by unattached quadrangular tube coiled into a flat spiral (hence the generic name) with the fossil Nogrobs de Montfort, 1808 and suggested that Bathyditrupa hovei might belong to the subgenus Nogrobs (Tetraditrupa) Regenhardt, 1961 . In their review, ten Hove & Kupriyanova (2009) followed Jäger (2004) and used the name Nogrobs for the former Spirodiscus grimaldii , but retained Bathyditrupa as a valid genus.

Zibrowius (pers. comm.) agrees that Bathyditrupa is mostly likely a synonym of Spirodiscus , but doubts that the name Nogrobs should be used for the extant material suggesting that the fossil tubes of “ Nogrobs ” may be so convergent that synonymising the Recent Spirodiscus would result in a loss of a well-defined genus. Based on his examination of unpublished material from collections of French deep-sea expeditions, Zibrowius (pers. comm.) suspects a total of at least four different species within Spirodiscus , some of them with not coiled quadrangular tubes similar to those of Bathyditrupa . The taxonomy of the entire Bathyditrupa / Nogrobs ( Spirodiscus ?)-complex is out of the scope of this study and a detailed world-wide revision of these taxa is needed. However, for the time being we follow ten Hove & Kupriyanova (2009) in treating Bathyditrupa as a separate valid genus.