Bathyvermilioides, Kupriyanova & Flaxman, 2024

Genus Bathyvermilioides View in CoL n. gen.

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Type species. Bathyvermilioides juliebrockae View in CoL n. sp.

Generic diagnosis. Tube white, opaque, tusk-shaped, quadrangular in cross-section, without peristomes. Operculum very hard, semi-globular shiny endplate. Peduncle cylindrical, smooth, without wings; inserted as 2 nd dorsal radiole on one side. Pseudoperculum absent. Radioles arranged in semi-circles, up to 12 per lobe. Inter-radiolar membrane and stylodes absent. Radiolar eyes and mouth palps absent. Seven thoracic chaetigerous segments. Collar trilobed, with entire edge, continuous with short thoracic membranes ending at 2 nd thoracic chaetiger. Tonguelets absent. Collar chaetae limbate. Apomatus View in CoL chaetae present. Thoracic uncini saw-shaped with 9–10 teeth in profile, anterior fang pointed. Triangular depression absent. Abdominal chaetae short, flat triangular with wide distal denticulate blade; abdominal uncini rasp-shaped, anterior fang pointed. Achaetous anterior abdominal zone absent. Long posterior capillary chaetae absent. Posterior glandular pad absent.

Remarks. The new genus Bathyvermilioides has tusk-shaped quadrangular in cross-section tubes resembling those of nominal Bathyditrupa and Spirodiscus , but the similarities end here, and quadrangular tubes are apparently convergent in several genera of deep-sea serpulids (Kupriyanova & Ippolitov, 2015). The genus clearly belongs to the subfamily Filograninae as indicated by the presence of the thoracic Apomatus chaetae and flat geniculate abdominal chaetae and which is supported by molecular results here ( Fig. 1 View Figure 1 ).

The results of the phylogenetic analysis here ( Fig. 1 View Figure 1 ) showed that the new taxon does not fall into the Bathyvermilia clade (type species B. challengeri ) but belongs to the well supported clade with Rhodopsis pusilla , Semivermilia , and Pseudovermilia . The phylogenetic position of B. juliebrockae n. gen., n. sp. suggests that the new taxon could have been included in the genus Rhodopsis . However, the taxa are very different morphologically, as the two currently valid species of the genus Rhodopsis are tiny, with the tubes <0.2 mm in diameter and often bearing unpaired brood chambers. The operculum in Rhodopsis is usually covered with a well-developed soft chitinous endplate bearing spines, the number of thoracic chaetigerous segments varies from four to six, and the achaetous anterior abdominal zone is long. Chaetal characters also differ in the two taxa as in Rhodopsis collar chaetae are absent, both thoracic and abdominal uncini are rasp-shaped, and abdominal chaetae are flat narrow geniculate.

Morphologically the new species most closely resembles Bathyvermilia gregrousei , a deep-sea species inhabiting similarly quadrangular, although smaller and slightly spirally twisted, tubes. It is likely that the Bathyvermilia gregrousei also should be transferred to the new genus, but molecular data are needed to confirm this hypothesis. Because of these morphological similarities with Bathyvermilia and phylogenetic position of the new species we established the new genus Bathyvermilioides . The suffix -oides means “similar to”. This taxonomical decision will again be tested in future molecular studies of deep-sea serpulids.