Thalassomyces fagei, an ellobiopsid parasite of the euphausiid crustacean, Thysanoessa raschi

Abstract

The development of an ellobiopsid parasite,Thalassomyces fagei (Boschma), within the cephalothorax of an euphausiid,Thysanoessa raschi (M. Sars), is described for the first time. The tissues of the young stages of the parasite have no intimate connexions with those of the host but become fused with them when the trophomeres begin to differentiate into a series of gonomeres. The parasites are found inT. raschi but have not been found in recent years in the associated population of the euphausiid,Meganyctiphanes norvegica (M. Sars), although it was recorded in one specimen of this species in 1925. The older stages of this parasite only occur inT. raschi in the Clyde during the period March-June but they have been recorded in the same species and other species of Northern Atlantic euphausiids in other sea areas later in the year. No fresh evidence has been found to decide whether these parasites have dinoflagellate, rhizopod, or fungal affinities.