A new cave-dwelling genus and species of Nerillidae (Annelida) from the Ryukyu Islands, Japan

Abstract

A new genus and species of Nerillidae, Nipponerilla irabuensis gen. nov., sp. nov., is described from an anchialine cave in Shimoji Island, west of Irabu Island (Miyako Islands, Southwestern Japan). Its morphology was examined with light, scanning electron, and confocal laser scanning microscopy. This new species, along with two putative new cave species from the Turks and Caicos Islands and several closely related nerillids, was included in a phylogenetic analysis employing five concatenated gene markers (16S rRNA, 18S rRNA, 28S rRNA, H3, and COI). Nipponerilla irabuensis gen. nov., sp. nov. was found to be sister taxon to the cave-exclusive genus Speleonerilla Worsaae, Sterrer & Iliffe, in Worsaae et al., 2019, but shows morphological resemblance to both Speleonerilla and Mesonerilla Remane, 1949. Thus, Nipponerilla gen. nov. constitutes a new monotypic genus in Nerillidae diagnosed by a combination of the following characters: nine segments, compound chaetae, high palp and antennae to body length ratios, and gonochoristic reproduction with two pairs of spermioducts opening in segments VII and VIII. Its placement among Nerillidae is discussed, along with its putative adaptations to an anchialine environment.

A new species of free-living marine nematode, Fotolaimus cavus sp. nov. (Nematoda, Oncholaimida, Oncholaimidae), isolated from a submarine anchialine cave in the Ryukyu Islands, southwestern Japan

“…In the present study, we describe a new species of the free-living marine nematode genus Fotolaimus Belogurova & Belogurov, 1974 collected from an anchialine cave called Akuma-no-yakata (= Devil's Palace) and located on the Shimoji Island (or Shimojijima Island), Miyako Island Group, Ryukyu Islands, southwestern Japan. Osawa and Fujita (2019) have provided a detailed description of this cave, and faunal surveys conducted in Akuma-no-yakata in recent years identified the following organisms in the cave: crustaceans (Fujita et al 2013(Fujita et al , 2017Anker and Fujita 2014;Fujita 2016, 2019;Fujita 2018, 2020;Saito and Fujita 2022), ophiuroids Fujita 2018, 2019), annelids (Worsaae et al 2021), molluscs (Mizuyama et al 2022), sponges (Ise et al 2023), and pycnogonids (Kakui and Fujita 2023). Belogurova and Belogurov (1974) established the genus Fotolaimus in Oncholaimidae Filipjev, 1916. Currently, this genus contains two species, i.e., F. marinus Belogurova & Belogurov, 1974 (type species) and F. apostematus (Wieser, 1959) Belogurova & Belogurov, 1974.…”

New sea spider species (Pycnogonida: Austrodecidae) from a submarine cave in Japan

“…Saito and Fujita, 2022), polychaetous annelids (e.g. Worsaae et al ., 2021), brittle stars (e.g. Okanishi and Fujita, 2019) and bivalves (e.g.…”