Kinorhynch fauna from Oki Islands, with the description of a new Echinoderes species and its phylogenetic relationships within the family Echinoderidae

A survey of the kinorhynch fauna in the Oki Islands revealed six species of kinorhynchs in three families and four genera. Among these, one species in the genus Echinoderes was described as a new species, Echinoderes okiensis sp. nov., based on the following characteristics: presence of middorsal acicular spines on segments 4–8; ventrolateral tubes on segment 2; lateroventral tubes on segment 5; lateroventral acicular spines on segments 6–9; midlateral tubes on segment 10; type-1 glandular cell outlets present middorsally on segments 1–3, 5, and 7, two middorsally on segments 10 and 11, one pair paradorsally on segments 4, 6, 8, and 9, sublaterally on segment 1, and ventromedially on segments 2–10; type-2 glandular cell outlets absent; tergal extension narrowing abruptly into long acicular tips, constituting 5–7% of trunk length; males with three pairs of penile spines, the middle pair being very short; females with papillae in ventrolateral position on segment 7 and ventromedial position on segment 8, as well as with lateral terminal accessory spines. This species was also found to inhabit off Iejima Island in Okinawa, more than 1000 km away from the Oki Islands. Phylogenetic analysis based on 18S and 28S rDNA sequences suggested that this species is closely related to Echinoderes aureus Adrianov et al., 2002 in the family Echinoderidae. These two species, along with the Echinoderes dujardinii species group, the Echinoderes spinifurca species group, Echinoderes truncates Higgins, 1983, and Cephalorhyncha, compose one of the two major clades detected in Echinoderidae.