Microscopic anatomy,functional morphology,and ultrastructure of the stomach of Euphausia superba Dana (Crustacea,Euphausiacea)

Summary Microscopic anatomy, functional morphology, and ultrastructure of the stomach of the antarctic krill Euphausia superba Dana were investigated by means of serial sections, scanning and transmission electron microscopy, and video technique. A separation of the stomach into an anterior part, called cardia, and a posterior part, called pylorus, became evident. Protrusions of the stomach into the midgut form the third region, called the funnel. The interior of the cardia is dominated by the two lateralia, originating from the side walls of the stomach. At their undersurface, they bear the primary filter. It separates the dorsal food channel from the ventral filtration channel, which is divided into two channels by a ventromedian ridge, the anteromedianum. Within the pylorus, the inferolateralia act in sealing the food channel from the filtration channel. In contrast to many other Malacostraca, the inferomedianum bears no secondary filter. During live observations, the stomach of Euphausia superba shows distinct pumping phases. A comparison of the structure of the stomach with data obtained from other Crustacea will lead to a better understanding about the relationships between the Malacostraca.