Three New Species of Spectrarcturus (Isopoda: Valvifera: Arcturidae) from Kumano Basin, Southwestern Japan

Three new species of the genus Spectrarcturus Schultz, 1981 (Arcturidae) are described from Kumano-Basin, Japan: S. regularis sp. nov., S. bispinosus sp. nov., and S. crassibrevis sp. nov. Spectrarcturus regularis sp. nov. resembles S. murdochi (Benedict, 1898) from North Pacific and Arctic waters around Greenland, S. hystrix (Sars, 1877) from northernmost North Atlantic Ocean, and S. intermedius (Richardson, 1899) from northernmost North Pacific, in the following features: head with 2 supraocular spines; pereonites 1–3 and 5–7 each with 2 submedial spines; pleon with 6 lateral spines. However, S. regularis sp. nov. is distinguished from these three species by the following combination of characters: body covered with long spines; head with 2 supraocular spines and 2 posterior supraocular spines; pereonite 1 with 2 submedial and 4 lateral spines; pereonites 2 to 7 with 2 submedial spines. Spectrarcturus bispinosus sp. nov. is separated from its congeners by the following combination of characters: body with numerous small tubercles; pereonite 3 with 2 blunt submedial spines. Spectrarcturus crassibrevis sp. nov. differs from its congeners by the following combination of characters: pereonites 1–7 each with 2–4 short blunt submedial spines; pleotelson with 4 short blunt submedial and 2 lateral spines. This study provides the first species of the genus to be described and found in Japan, and southernmost distributional record of the genus. An amended diagnosis of the genus and key to the species are provided.