The copepod Lernaea sp. was found parasitizing 14 of 28 species of fishes collected from the Des Moines River, Iowa. Forty-nine diatom taxa from 15 genera were identified in a collection prepared by digestion of 50 algal-covered copepods. No diatoms were observed on copepods collected from the lower zone of the river. Members of the diatom genus Gomphonema were the most abundant forms and provided a suitable habitat for other diatoms by secreting extracellular polysac- charide stalks. ! l l | g g i .: . ; . ;~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~.e ... ....... ... iel o. ! | :\...n:D..Dl . . .~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^+- wii ; W0.::: : . .. t e - |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~