A new species of Dendrogaster Knipowitsch, 1890 (Thecostraca: Ascothoracida: Dendrogasteridae) parasitic in the sea star Certonardoa semiregularis (Muller & Troschel, 1842) (Echinodermata: Asteroidea) from Japan

An ascothoracidan crustacean of the genus Dendrogaster Knipowitsch, 1890 (Dendrogasteridae), known for more than 80 years to infect the sea star Certonardoa semiregularis (Muller & Troschel, 1842) and previously identified as Dendrogaster ludwigi Le Roi, 1905, is described as a new species on the basis of recently collected specimens from Mie and Yamaguchi Prefectures, Japan. Dendrogaster adhaerens n. sp. was found within the coelomic cavity of the arms of its host sea star. Partial sequences of the cytochrome c oxidase subunit I (COI) gene show that the specimens from both localities are conspecific. This new species was also confirmed to be morphologically distinct from Dendrogaster sp. cf. ludwigi infecting Echinaster luzonicus (Gray, 1842), which has also been confused with D. ludwigi. The new species differs from all of its congeners in the anastomosis of the posterior primary branches and its adhesion to the inner body wall of the host.