Scanning and transmission electron microscopic observations on the stomach of three mysid species (Crustacea).

Epithelial and cuticular linings of the stomach investigated in three species representing different genera of the Mysidacea are elaborated into a set of structural specializations dividing the stomach longitudinally into one dorsal and two ventral channels. The dorsal, or food, channel contains ingested food and retains coarse particles, which eventually are transported into the midgut through a funnel. The ventral, or filtration, channels, which are separated by an anterior and a posterior median ridge (anteromedianum, inferomedianum), contain fine particles and soluble materials extracted from the dorsal channel through two filter systems: primary filters, which lie anteriorly on either side of the anteromedianum, and posterior secondary filters, which are located on the inferomedianum. The final filtrate is transported into the ventral caeca or midgut glands. The ultrastructure of the cuticle lining the lumen of the stomach shows several specializations, the most prominent of which are stout spines and delicate filter devices. The epithelium is multilayered in circumscribed areas (the lateralia). The basement lamina is extremely developed in the inferomedianum. Detailed knowledge of the microscopic anatomy and the ultrastructure of the stomach allows identification of several homologous gastric structures among different peracaridean groups and in Decapoda.