Crayfish worms (Branchiobdellidae) are obligatory ectosymbionts of crustaceans, primarily crayfish. Little is known about their diets or ecology. A single crayfish can host several species and age classes of branchiobdellidans at one time, creating the potential for intra- and inter-specific
competition. Coexistence of competitors can be promoted through dietary differences; therefore, we examined gut contents of Cambarincola chirocephalus Ellis, 1919 and
Cambarincola vitreus Ellis, 1919, two species of branchiobdellidan occasionally found on the same host (the crayfish Orconectes virilis (Hagen, 1870)
in Western Canada) to assess evidence of dietary niche partitioning. We also compared gut contents of conspecific adults and juveniles to determine whether diets differed with age. We found a range of diatoms and invertebrates, particularly rotifers, in the guts of both Cambarincola
species. The species appear to have different diets, in that guts of C. chirocephalus contained more invertebrate material than did those of C. vitreus. There was no statistical difference in composition of gut contents between adult and juvenile conspecifics. We found
very limited evidence of dietary niche expansion in C. vitreus in the absence of C. chirocephalus. The observed dietary differences between species may promote their continued coexistence in areas where their ranges overlap.
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