Hyalopomatus Marenzeller 1878

Hyalopomatus Marenzeller, 1878

Type-species: Hyalopomatus claparedii Marenzeller, 1878

Generic diagnosis (after Kupriyanova et al. 2010). Tube white, opaque, sometimes with external hyaline layer, but granular overlay absent; (semi) circular in cross-section. Exceptionally for this genus, Hyalopomatus variorugosus Ben-Eliahu & Fiege, 1996 characterized by tubes with minute flap–like structures, and Hyalopomatus biformis by tubes with longitudinal ridge (Bastida-Zavala 2008). Tabulae may be present. Operculum globular, soft, without distinct endplate or consisting of proximal ampulla with slightly chitinized distal cap; conspicuous constriction between operculum and peduncle; sometimes operculum absent. Peduncle sometimes thin (same thickness as radioles), cylindrical, smooth, wings absent; inserted outside branchial crown proper in front of 1st dorsal radiole on either side or between base of 1st and 2nd radioles. Pseudoperculum absent. Up to 15 pairs of radioles, in pectinate arrangement. Inter-radiolar membrane absent. Branchial eyes rarely present. Stylodes absent. Mouth palps present. Six thoracic chaetigerous segments, 5 of which uncinigerous. Collar trilobed, tonguelets absent. Thoracic membranes short, ending at 1st or 2nd chaetiger. Collar chaetae simple limbate capillaries and fin-and-blade, with or without gap between fin and blade. Apomatus chaetae absent. Thoracic uncini rasp-shaped with about 20 small teeth, in profile view, up to nine teeth in a transverse row above flat or slightly gouged anterior peg made of two or more rounded lobes with shallow incision(s) in between. Triangular depression absent. Abdominal chaetae ending in long narrow tip made of pointed teeth that at least partly arranged in two rows on anterior and mid-abdominal segments, long capillaries on posterior chaetigers. Abdominal uncini rasp-shaped, similar to thoracic ones, but their anterior peg with 3–6 flat rounded lobes. Achaetous anterior abdominal zone may present. Posterior glandular pad absent.

Remarks. The recent review by ten Hove & Kupriyanova (2009) listed 12 species of Hyalopomatus known mainly from bathyal and abyssal depths. Sanfilippo (2009) added one more species from the Mediterranean. Four species have been reported from the Pacific Ocean: Hyalopomatus biformis (Hartman, 1960), Alaska to Southern California; H. jirkovi Kupriyanova, 1993a, Kurile-Kamchatka Trench; H. mironovi Kupriyanova, 1993a, Kurile- Kamchatka Trench, off California; H. sikorskii Kupriyanova, 1993a, Kurile-Kamchatka Trench. Most recently H. mironovi was also recorded from hydrothermal vents off North Fiji (Kupriyanova et al. 2010) and H. biformis from the Patton-Murray Seamount in Gulf of Alaska (Kupriyanova & Nishi 2010).

Kupriyanova et al. (2010) suggested that crenulated uncinal pegs (visible in SEM micrographs) is a clear synapomorphy for the genus Hyalopomatu s. Also, SEM micrographs of abdominal chaetae in H. mironovi and H. biformis (Kupriyanova et al. 2010, Kupriyanova & Nishi 2010) show that the tips of abdominal chaetae in those species are not “flat narrow” as stated by ten Hove & Kupriyanova (2009), but have denticles arranged in two rows at least partly. Further SEM studies of abdominal chaetae in Hyalopomatus spp., are needed. Along with the distinct structure of the uncini, six thoracic chaetigers and a vesicular operculum on smooth (usually thin) peduncle make Hyalopomatus relatively easily distinguishable from other serpulid genera, but the species within this genus are morphologically very similar to each other. The much needed revision of this poorly known genus is currently underway (Kupriyanova & Sanfilippo in prep.).