ULTRASTRUCTURE AND FUNCTIONAL MORPHOLOGY OF FEEDING AND ASSOCIATED APPENDAGES IN THE TROPICAL FRESH-WATER SHRIMP ATYA INNOCOUS (HERBST) WITH NOTES ON ITS ECOLOGY

Abstract

ABSTRACT Atya innocous (Atyidae) occurs in permanent and temporary fresh-water streams in Panama. Its microhabitat distribution depends in part on the presence of congeners. The propodus and dactylus of each cheliped of A. innocous bear about 300 setae modified for specific functions in food collection. These setae may be divided into three basic types: chemoreceptors, scrapers, and filtering setae. The latter two types also function as mechanoreceptors. The cheliped setae are probably extended by an increase in hemocoelic pressure, producing an efficient filtering fan. Mechanosensory and chemosensory bipolar neurons innervate the cheliped setae, presumably providing the shrimp with the ability to detect current velocity, particulate load, and quality of the food source. The external morphology and ulrastructure of these sensilla are described. No dually innervated receptors (mechanochemoreceptors) were found. In addition to food collection and sensory functions, the pereiopods are used to groom body parts and brooded embryos. Super-8 eine films show the important role mouthparts play in grooming. The third maxillipeds groom the antennae and antennules, while the ultimate segment of the second maxillipeds frees lodged debris from the chelipeds. The dactylar pectinate comb of the fifth pereopod grooms the dorsal surface of the abdomen and pleopods. Scanning electron microscopy showed pores in the cuticle leading to unicellular and multicellular glands within the epidermis. Three gland types were observed and their respective functions are described. Adaptations for a lotic habitat seem to be important to species of Atya, which have a wide array of morphological modifications for life in running water.