A brackish water mud dragon species Echinoderes filispinosus is redescribed from the type locality in the Sea of Japan. The species should be considered part of the Echinoderes coulli species group. This species is characterized by presence of a single minute middorsal spine on trunk segment 4, minute lateroventral spines on trunk segments 6–7, long lateroventral tubes on trunk segments 5 and 8, sexually dimorphic laterodorsal tubes on trunk segment 10, numerous glandular cell outlets type 2 modified into minute fringed tubes, large elongated sieve plates with posterior pore, and strongly reduced lateral terminal accessory spines. The paper documents newly found morphological characters of E. filispinosus, suggesting an emended classification of Echinoderes ohtsukai as junior synonym of E. filispinosus. DNA sequence also reveals that E. ohtsukai is completely conspecific with E. filispinosus. This estuarine species demonstrates outstanding ability to survive under the record seasonal variations of temperature and salinity. Transoceanic distribution of this species in the North Pacific is also discussed.
Brackish water, Echinoderes, Estuary, Kinorhynchs, Transoceanic
