Sea spiders (Arthropoda: Pycnogonida) from waters adjacent to the Nansei Islands of Japan

About 160 species of pycnogonids have been reported from Japan. Among these, only 18 species have been reported from the extensive archipelago of the Nansei (southwest) Islands, even though this warm‐temperate to subtropical region should have a pycnogonid fauna as rich as or richer than that surrounding the Japanese main islands. We provide descriptions for five species of pycnogonids collected from depths of 52–334 m along the continental shelf adjacent to the Nansei Islands. Rhopalorhynchus tenuissimum (Haswell, 1884) is the first record of this genus and species for Japan, and Pycnogonum tenue Slater, 1879 is a new record for the Nansei Island region; we report some previously unrecognized taxonomic characters for these species. We describe as new species Endeis leviseminentia, Hedgpethia elongata, and Pycnogonum spatium.