Abstract
Echinomermella matsi sp. n. is described from the pervisceral coelom of the sea urchin Strongylocentrotus droebachiensis MÜLLER in Vestfjorden northern Norway. Morphologically E. matsi resembles the enoplid Mermithoidea, with an extremely reduced oesophagus, intestinal trophosome, and vestigal rectum and anus, and closely resembles Echinomermella grayi (GEMMILL, 1901) previously described from Echinus esculentus L. Both nematodes are atypical mermithoids since the parasitic stage is the adult, not juvenile, and females are ovoviviparous with retention of eggs and larvae in the pseudocoelom; vulva and vagina have not been seen. The occurrence of E. matsi is limited to S. droebachiensis although Echinus esculentus and Strongylocentrotus pallidus G.O. SARS co-occur in the study area.
