Comparative Study of Ultrastructure of Interlamellar and Intralamellar Types of Henneguya exilis Kudo from Channel Catfish*†

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Abstract
The inter- and intralamellar types of H. exilis (Myxosporida) infections from channel catfish [Ictalurus punctatus] are similar in spore structure and sporogenesis, but differ in the structure of their plasmodium wall and surface coat and in their relationship with the host cells. The 2 clinical types differ in the sites of development and growth patterns of plasmodia within a gill filament. Interlamellar plasmodia are limited by 2 outer unit membranes which give rise to single- and double-membraned pinocytic canals. Intralamellar plasmodia are limited by a single outer unit membrane which gives rise to single-membraned pinocytic canals. Interlamellar plasmodia are covered by a fine granular coat of highly variable thickness; in some regions there is direct contact between the parasite and cells of the host. There is some evidence that host cell cytoplasm as well as interstitial material are taken in by interlamellar plasmodia. Intralamellar plasmodia are covered by a fine granular coat of almost uniform thickness, which prevents direct contact between the parasite and cells of the host; probably only interstitial material is taken by these plasmodia.