Hyalopomatus Marenzeller 1878

Genus Hyalopomatus Marenzeller, 1878

Type-species: Hyalopomatus claparedii Marenzeller, 1878

Diagnosis (from Kupriyanova et al. 2010).

Tube white, opaque, sometimes with external hyaline layer, but granular overlay absent; (semi) circular in cross-section; keels and collar-like rings mostly absent, tube interruptions may be present. Tabulae may be present. Operculum globular, soft, without distinct endplate or consisting of proximal ampulla with slightly chitinized distal cap; well separated from peduncle by constriction; sometimes operculum absent. Peduncle very thin, cylindrical, smooth, without wings; inserted outside branchial crown proper in front of first dorsal radiole on one side or between base of first and second radiole. Pseudoperculum absent. Arrangement of radioles short pectinate, up to 15 pairs of radioles. Inter-radiolar membrane absent. Branchial eyes rarely present. Stylodes absent. Mouth palps present. Six thoracic chaetigerous segments. Collar trilobed, tonguelets absent. Thoracic membranes short, ending at first or second thoracic chaetiger. Collar chaetae fin-and-blade, with or without gap between fin and blade and thus with uniform distal denticulate wing, and limbate blade (H. claparedii lacks distinct fin-and-blade special collar chaetae). Apomatus chaetae absent. Thoracic uncini rasp-shaped with numerous small teeth, approximately 20 in profile, up to 9 teeth in a row above peg; anterior peg made of two or more rounded lobes with shallow incision(s) in between, flat or slightly gouged in the middle. Triangular depression absent. Abdominal chaetae almost capillary ending in a long narrow tip made of pointed teeth that may be partly arranged in two rows; uncini rasp-shaped, similar to thoracic ones, but their anterior peg with 3–6 flat rounded lobes. Achaetous anterior abdominal zone may be present. Posterior capillary chaetae present. Posterior glandular pad absent.

Remarks. The genus currently contains 13 poorly known species from bathyal and abyssal depths. Although the soft body features are very similar within the genus, tube structure provides additional characters that distinguish species, for example, tubes of Hyalopomatus variorugosus Ben-Eliahu & Fiege, 1996 are characterized by minute flap-like structures, the attached part of the H. biformis (Hartman, 1960) tube has a high longitudinal ridge (Bastida-Zavala 2008), H. langerhansi has slight lateral keels in the part attached to the substratum (Zibrowius 1969), and H. madreporae Sanfilippo, 2009 described based on empty tubes only has very characteristic tube interruptions.