O. eutrophila is dimorphic, with males being than females, while possessing K-type maxillae.

Ophryotrocha eutrophila, however, differs from O. puerilis in the absence of eyes and the presence of a developed median pygidial stylus.

It also counts with two peristomial segments without setae, its parapodia being uniramous and showing short dorsal and ventral cirri.

Its pygidium has a terminal anus, with two pygidial cirri being laterally inserted, as well as an unpaired appendage that is placed ventrally.

[1] It was first found in a minke whale carcass at a depth of 125 metres (410 ft) in the Koster area in Sweden.