FEEDING STRUCTURES OF 2 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 foregut are compared to test the hypothesis that these structures are related to diet. A. innocous occurs in moderate to fast-flowing streams, feeding on minute particles collected from the water column or bottom. P. glabra inhabits quiet pools, scrapping periphyton from leaf surfaces and decaying organic detritus. The feeding appendages of boths species are 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.