Feeding Structures of Two Atyid Shrimps, with Comments on Caridean Phylogeny

Atya innocous and Potimirim glabra (Atyidae) occur in permanent and temporary freshwater streams in the Atlantic and Pacific drainages of Panama. Their mouthparts, mandibles, and foreguts are compared to test the hypothesis that these structures are related to diet. Atya innocous occurs in moderate to fast-flowing streams, feeding on minute particles collected from the water column or bottom. Potimirim glabra inhabits quiet pools, scraping periphyton from leaf surfaces and decaying organic detritus. The feeding appendages of both species arc modified for handling fine particles of food. The mandibles have a strong incisor process but are not used for crushing large food items. The primitive nature of the mandible and foregut suggests the placement of the family Atyidae at the base of the caridean evolutionary tree. The use of the foregut in the construction of phylogenies within the Decapoda is discussed.