Echinoderes xiphophorus sp. nov. – the first deep-water representative of Echinoderidae in the Sea of Japan (Kinorhyncha: Cyclorhagida)

Andrey V Adrianov,Anastassya S Maiorova

doi:10.5852/ejt.2021.773.1523

Abstract

A new species of echinoderid kinorhynchs, Echinoderes xiphophorus sp. nov. collected from oxidized brown silt at the deepest depression in the Sea of Japan, North-West Pacific, is described and illustrated using light and electron microscopy. This new representative of the most speciose kinorhynch genus is characterized by the unique set of spines and tubes and can easily be distinguished from most of its congeners. The second trunk segment bears three pairs of tubes in subdorsal, midlateral and ventrolateral position in both sexes; one pair of tubes on trunk segment 5 in lateroventral position and on trunk segment 8 in sublateral position; aciculate lateroventral spines on trunk segments 6–9; aciculate middorsal spines on trunk segments 4, 6, 8. This species is well recognized by very long tergal extensions of the posteriormost segment, some of the longest within the family Echinoderidae. Males of Echinoderes xiphophorus sp. nov. are well distinguished from all the congeners by extremely long sword-like appendages dorsally to three pairs of penile spines. The species constitutes the first deep-sea representative of the Echinoderidae in the Sea of Japan and the deepest representative of the Kinorhyncha in this sea.

Highlights

Kinorhynchs are meiobenthic free-living segmented worms, from 0.2 to 1.2 mm in length
On the slope of the deepest depression in the Sea of Japan, near the Russian coast, at a depth of 1530 m, we found a new species of echinoderid kinorhynchs with unique morphological characters
The specimens here described as a new species, Echinoderes xiphophorus sp. nov., were collected from an oxidized brown clay taken by multiple corer (MUC) on a slope at the deepest depression in the western part of the Sea of Japan at a depth 1530 m (44.7942° N and 137.2550° E)

Summary

Introduction

Kinorhynchs are meiobenthic free-living segmented worms, from 0.2 to 1.2 mm in length. They are worldwide in distribution, inhabiting the upper few centimeters of various marine sediments from the littoral zone to the hadal depth up to 9538 m (see Adrianov & Maiorova 2019). As reported in some recent papers, kinorhynchs are very common and numerous in the abyss and even in the hadal zone (see Neuhaus 2013; Adrianov & Maiorova 2015, 2016, 2018a, 2018b, 2019, 2020; Sørensen et al 2018; Yamasaki et al 2018a, 2018b, 2018c). Information on the species composition in the deep sea is still very limited. Six species of Echinoderes Claparède, 1863 have been described from the Sea of Japan: E. filispinosus

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