Abstract
A marine armoured tardigrade, Hansenarctus toyoshiomaruae gen. et sp. nov., is described from Yaku-Shin-Sone bank, south of Yakushima island, Northwest Pacific. It belongs to the family Stygarctidae Schulz, 1951 for its five-lobed head, cuticular plates, and non-digitate claws, but a combination of the following character states warrants the erection of the new genus: the semi-globular secondary clavae, sub-divided lateral lobes of the head, antero-dorsal, postero-dorsal, and latero-dorsal processes on the dorsal plates except for the caudal plate, two tapering lateral processes (one pair) on each body plate, four lateral processes (two pairs) on the caudal plate, intersegmental regions between dorsal plates, looped seminal receptacles without additional cuticular structures at the openings, and four claws with the internal ones bearing dorsal spurs. Its phylogenetic position is briefly discussed based on morphology and the following topology was suggested for Stygarctidae: (Megastygarctides, (Neostygarctus, (Faroestygarctus, Hansenarctus gen. nov., (Mesostygarctus, Pseudostygarctus), (Parastygarctus, Prostygarctus, Stygarctus)))). Stygarctid genera (excluding Megastygarctides and Neostygarctus) share a synapomorphic state: the presence of exteriorly projected apophyses in the pharyngeal bulb.
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