Electron microscopical study of a new genus and new species of microsporida in the gills of Atlantic cod Gadus morhua L.*

A microsporidium, forming xenoparasitic complexes (xencmas) of the cell‐hypertrophy tumour type, was found in the gills of the Atlantic cod Gadus morhua L. and studied with the electron microscope. It seemed to be similar to Nosema branchiate Nemeczek, 1911, in the haddock Melanogrammus aeglefinus (L.) except in size of spore. The xenoma (cyst) was basically like the Glugea cyst and the parasite had some other characters in common with Glugea; it was apansporoblastic, unikaryotic, disporoblastic and underwent partial development in parasitophorous vacuoles. It differed from Glugea in lacking plasmodial stages, producing usually 1 or 2 spores (rather than 16) in a vacuole, showing no distinct tendency for different stages to occur in different zones of the cyst and having tubules in the parasitophorous vacuoles. The name Loma morhua n. g., n. sp. (type) was proposed and the genus assigned to the family Glugeidae Thélohan, 1892. The parasite of haddock gill was transferred to the new genus, becoming L. branchialis (Nemeczek, 1911) n. comb.