A new species of the mysterious genus Spirodiscus (Annelida: Serpulidae) of the eastern Australian abyss

In May–June 2017 an expedition on board RV Investigator sampled benthic communities along the lower slope and abyss of Australia’s eastern margin from off mid-Tasmania to the Coral Sea. Over 200 annelids of the family Serpulidae collected during the voyage were collected and deposited in the Australian Museum in Sydney. Among them there was a new species of the poorly known abyssal (3754–4378 m) genus Spirodiscus. Serpulids typically build cylindrical calcareous tubes attached to hard substrates. Until now, only three serpulid species inhabiting free-lying polygonal tubes were reported from the deep sea: Spirodiscus grimaldii Fauvel, 1909 with quadrangular spirally coiled tubes, Bathyditrupa hovei Kupriyanova, 1993 with quadrangular tusk-shaped tubes, and Spirodiscus groenlandicus (McIntosh, 1877) with octagonal tusk-shaped tubes. The new species, S. ottofinamusi sp. nov. has very characteristic thin tusk-shaped unattached fluted tubes similar to those found in S. groenlandicus, but it differs by the details of collar, thoracic tori and abdominal chaetae. Morphologically, it has a pinnulated opercular peduncle and flat geniculate abdominal chaetae like filogranin serpulids but lacks thoracic Apomatus chaetae like serpulins. The first DNA sequences of this mysterious taxon places the new species within the filogranins in sister group relationship with Chitinopoma serrula.