Comparative morphology of the foregut of three Eucopia species (Crustacea, Mysidacea, Lophogastrida)

The features of the foregut of Eucopia sculpticauda Faxon, 1893, E. unguiculata W.-Suhm, 1875 and E. australis Dana, 1852 (Lophogastrida, Mysidacea) are described, based on scanning electron microscopy. The foregut consists of a vertical oesophagus and an elongated stomach which is functionally divided into anterior cardiac, posterior pyloric and funnel regions. The pyloric chamber is longer than the cardiac chamber. Structural outgrowths of the cuticle, lining the foregut, divide the stomach longitudinally into one dorsal and two ventral channels. The dorsal, or food, channel contains ingested material and retains coarse particles, which are broken down during mastication by the gastric mill of the cardiac chamber and eventually transported into the midgut through the funnel. The ventral, or filtration, channels, which are separated by an anterior and posterior median ridge, contain fine particules and soluble materials extracted from the dorsal channel through two filter systems: the primary filter of the cardiac chamber and the secondary filters of the pyloric chamber. The foregut of Eucopia exhibits more similarities with that of the Decapoda than of Mysida. It seems to be morphologically specific to this genus, although each species exhibits specific differences: e.g. the gastric mill of Eucopia sculpticauda is characterized by the presence of an unpaired antero-cardiac dorsal tooth and of spines with apical pore on the first lateral cardiac teeth.