Ficopomatini Pillai, 1960

Tribe Ficopomatini Pillai, 1960 View in CoL sensu

Kupriyanova et al., 2023

Tribe diagnosis. Tube not spirally coiled; body symmetrical; thoracic sickle ( Apomatus ) chaetae always absent; abdominal chaetae true trumpet-shaped.

Genus Hyalopomatus Marenzeller, 1878 View in CoL

Type species. Hyalopomatus claparedii Marenzeller, 1878 View in CoL

Generic diagnosis (after Kupriyanova & Ippolitov, 2015). Tube white, opaque, sometimes with external hyaline layer; (semi) circular or quadrangular with rounded edges in cross-section. 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 thin (same thickness as radioles), cylindrical, smooth, wings absent; inserted outside radiolar crown proper in front of 1 st dorsal radiole on either side or between base of 1 st and 2 nd radioles. Pseudoperculum absent. Up to 15 pairs of radioles, in pectinate arrangement. Inter-radiolar membrane absent. Radiolar eyes rarely present. Stylodes absent. Mouth palps present. Six thoracic chaetigerous segments, 5 of which uncinigerous. Collar trilobed, tonguelets between ventral and lateral collar lobes absent. Thoracic membranes short, ending at 1 st or 2 nd chaetiger. Collar chaetae simple limbate capillaries and fin-and-blade, with or without gap between fin and blade. Apomatus View in CoL chaetae absent. Thoracic uncini rasp-shaped with about 20 small teeth in profile view, up to 9 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 be present. Posterior glandular pad absent.

Remarks: The genus Hyalopomatus currently contains 14 nominal species mainly from bathyal and abyssal depths (ten Hove & Kupriyanova, 2009; Kupriyanova et al., 2011, Kupriyanova & Ippolitov, 2015). Likely because of the deep-sea habitat, these animals are poorly known. In fact, six ( Hyalopomatus cancerum Knight-Jones et al., 1997 ; H. dieteri Kupriyanova & Ippolitov, 2015 ; H. langerhansi Ehlers, 1887 ; H. nigropileatus Ehlers, 1900 ; H. macintoshi Gravier, 1911 ; and H. sombrerianus ( McIntosh, 1885)) out of 14 currently valid species are known only by few specimens.

Morphologically, the species of Hyalopomatus are characterized by six thoracic chaetigers, short thoracic membranes, vesicular opercula on thin non-pinnulated peduncle, fin-and-blade special collar chaetae and, most importantly, uncini with very distinct flat crenulated pegs. A smooth tube with a breaking point (likely a former peristome) (as in Fig. 12A View Figure 12 ) appears to be characteristic for the genus Hyalopomatus as such breaks are frequently illustrated (e.g., Hyalopomatus biformis , H. claparedii , H. madreporae , H. marenzelleri , and H. variorugosus ).

While the species of the genus are relatively easily distinguishable from representatives of other serpulid genera, the species within this genus tend to be morphologically similar to each other. The distinct species are Hyalopomatus madreporae Sanfilippo, 2009 and H. cancerum that lack opercula. Tube structure provides further characters to distinguish species within this genus: H. dieteri has characteristic quadrangular in cross-section tubes, tube surface of H. variorugosus is distinctly rugose because of characteristic minute flap-like structures, while the attached part of the H. biformis (Hartman, 1960) tube has a high keel (Bastida-Zavala, 2008) and tubes of H. langerhansi have slight lateral keels in the part attached to the substrate ( Zibrowius, 1969). The remaining 8 species have simple circular in cross-section tubes with smooth surface and differ by the details of opercular morphology, length of thoracic membranes, and collar structure. See remarks to new species described below.

Kupriyanova et al. (2010) emended the diagnosis of the genus Hyalopomatus because SEM of the abdominal chaetae of H. cf. mironovi Kupriyanova, 1993c revealed that their tips have the teeth arranged in two rows, at least at the base of the chaetal tip and are not “flat narrow geniculate with pointed teeth”. Thus, the abdominal chaetae appear to be a variation of true trumpet-shaped (sensu ten Hove & Kupriyanova, 2009) chaetae normally characterised by two rows of denticles separated by a hollow groove and extended into a long lateral spine. The tips of abdominal chaetae in H. biformis are similarly not flat but are arranged into at least two irregular rows (Kupriyanova & Nishi, 2010, fig.6C), and these tips are clearly true trumpet-shaped in H. dieteri (Kupriyanova & Ippolitov, 2015, fig. 12H). This type of abdominal chaetae is typical for representatives of tribe Ficopomatinae , which is also supported by molecular sequence data here ( Fig. 1 View Figure 1 ) and in Kupriyanova et al. (2023).