PLEISTOPHORA-FINISTERRENSIS N-SP, A MICROSPORIDIAN PARASITE OF BLUE WHITING MICROMESISTIUS-POUTASSOU

Pleistophora finisterrensis n. sp. is a microsporidian parasite of the hypoaxial musculature of the blue whiting Micromesistius poutassou (R isso). Foci of infection are between 3 and 6 mm in length and have no evident effects on adjacent muscle fibres. We found only a single type of spore (uninucleate, with mean dimensions of 4 x 2 mu m in fresh pr eparations), contained within sporophorous vesicles (mean diameter 19 mu m in fresh preparations; 150-250 spores per vesicle). All of the de velopment stages of this microsporidian are monokaryotic. The meronts are initially uninucleate and bounded by a plasmalemma. Towards the en d of merogony, meronts are multinucleate plasmodia with a well-defined surface coat. Sporogony is polysporous, with multinucleate sporonts, which likewise have a well-defined surface coat (about 130 mn thick), dividing by plasmotomy to give rise to uninucleate sporoblasts. The po lar tube is isofilar and consists of 8-9 turns in the posterior half o f spore. The polaroplast is made up of an anterior lamellar part and a posterior vesicular part.