Myxobolus microcystus sp. N. (Protozoa: Myxosporida) from the gills of Micropterus salmoides (Lacépède 1802) in southern Illinois.

Myxobolus microcystus sp. n. is described from the gills of the largemouth bass, Micropterus salmoides. Mean spore dimensions (in micrometers) are as follows: spore length 12.5; spore width 7.5; spore thickness 5.5; polar capsule length 6.5; polar capsule width 2.5; extended length of polar filaments 21 to 37; polar filaments with 6 to 7 coils. In histological sections, hyperplasia of infected filaments, atrophy of lamellae, partial occlusion of the efferent artery, and reduction in the number of peripheral goblet cells were observed.