Six new species of free-living nematodes (Nematoda: Enoplida) from deep-sea cold seeps on Hikurangi Margin, New Zealand

Little is known about the taxonomy of deep-sea nematode species inhabiting cold seep habitats. An opportunity to characterize the nematode species communities of New Zealand cold seeps was provided by a 2019 research voyage to New Zealand's Hikurangi Margin, during which macrofauna cores were obtained at two seeps at approximately 1,250 and 2,000 m water depth. Here, six new species of the orderEnoplida are described. Metacylicolaimus catherinae sp. nov. represents the first record of the genus for the New Zealand Exclusive Economic Zone and for the deep sea globally. Halalaimus talaurinus sp. nov., Thalassoalaimus duoporus sp. nov. and Crenopharynx crassipapilla sp. nov. are only the second species of their respective genera to be described/recorded from New Zealand waters, and Oncholaimus adustus sp. nov. is the eighth species of the genus to be recorded from the region. Rhabdodemania zealandiaensis sp. nov. was among the most abundant and widespread species found at the Hikurangi Margin seep sites. A few specimens had been found in a previous ecological study of meiofaunal nematode communities on Chatham Rise, a submarine ridge south of Hikurangi Margin. It is possible that this species has a preference for seep environments due to elevated food availability, however it does not seem to be exclusively found in seeps. We find no evidence for an affinity between nematode seep communities in New Zealand and elsewhere, which is consistent with the high variability in nematode community observed to date among regions. Ongoing work on the ecology and distribution of nematode communities at the Hikurangi Margin seep sites will help determine spatial patterns in abundance and species distributions in more detail, including the identification of any species/taxa with affinities with seeps.