A new deep-sea genus of Paramunnidae (Isopoda: Asellota) from the Northwest Pacific adjacent to the Kuril-Kamchatka Trench with remarks on paedomorphosis in deep-sea species.

• A new unusual abyssal genus of paramunnid isopods is described from the NW Pacific. • It is distinguished by paedomorphic features (reduced pereonite 7 that lacks legs) • Paedomorphosis seems to be an important adaptation for deep-sea life. • This phenomenon is a common evolutionary strategy for deep-sea Asellota. Reductogonium iroquois gen. nov. sp. nov., a new genus and species of paramunnid isopods from the Northwest Pacific open abyssal plain to the east of the Kuril-Kamchatka Trench, is described based on materials from the KuramBio expedition (2012). The new genus is distinguished from other paramunnid genera by its reduced pereonite 7 that lacks appendages in adult individuals (one seta is presented instead of the pereopod VII on its position). It is also distinguished by its head, which has a medial crest bearing a tuft of setae on its posterior part, and by the extremely long articles of antennae and pereopods. The unusual paedomorphic features of the new genus might be adaptations to deep-sea conditions. Paedomorphosis was recorded for different taxa of deep-sea animals. The reduction of the last pair of pereopods, which corresponds to the state of manca stages, was observed independently in different families and orders of Isopoda. Finding a new species and a new genus of the Paramunnidae with paedomorphic features confirmed that this phenomenon is a common evolutionary strategy for deep-sea Asellota. [ABSTRACT FROM AUTHOR]