DEVELOPMENT OF THE STOMACH IN EUPHAUSIA-SUPERBA DANA (EUPHAUSIACEA)

Development of the stomach, with emphasis on the filter system, was in vestigated in the metanauplius, calyptopis, and furcilia stages of the Antarctic krill Euphausia superba. The metanauplius lacks an elaborat ed stomach as well as a connection between the esophagus and the midgu t. In calyptopis I, the stomach becomes functional. The armature of th e cardiac stomach consists of basic components such as lateral and ven tral projections and stout spines, but not a primary filter. The latte r develops before molt beneath the cuticle and is seen in the exuvial space of calyptopis II. With molting to calyptopis III, the primary fi lter is elaborated and becomes capable of sorting food particles and o f separating a dorsal food from a ventral filtration channel. Although in furcilia IV the spacing of spines in the primary filter is nearly identical to that in the adult specimens, the filter spines in calypto pis III are more widely separated. In all larval stages examined (exce pt furcilia IV), the development of the pyloric stomach is delayed wit h respect to that of the cardiac stomach. Residues of a pyloric second ary filter system were not found in developing stages of Euphausia sup erba.