THE DIGESTIVE-SYSTEM OF RHYNCHOTEUTHION PARALARVAE (CEPHALOPODA, OMMASTREPHIDAE)

The anatomy of the digestive system and the digestive system enzymes o f three types of rhynchoteuthion paralarvae A ', B ', and C ' (Illex) were studied. No differences among the three were found. The main feat ures of the digestive system of these species of paralarval Ommastreph idae are described. The buccal mass is comprised of a beak and radula with conspicuous teeth. The well developed posterior salivary glands c ontain glandular tissue with two cell types: A, goblet cell, and B, gr anular cell. The esophagus is lined with a thin cuticle, but the stoma ch lacks cuticle and has a more strongly developed muscular wall than the esophagus. The large vestibule is lined with ciliated and glandula r cells. Some primary folds of ciliated epithelial cells begin to deve lop in the caecum. The digestive gland is compact, round, red-pigmente d and enclosed in a thick elastic capsule; it contains conspicuous inc lusions: large boules, typical brown-body vacuoles and numerous lipid droplets. Thirteen hydrolases involved in digestive processes were exa mined. High proteasic activity and histochemically undetectable amylas ic activity suggest a carnivorous diet. The occurrence of typical lyso somal enzymes in the digestive gland reveals a high intracellular dige stive activity. The digestive system appeared to be developed and func tional in the smallest specimens examined (ML: mantle length 1-2 mm). Typically juvenile features include the anterior part of the digestive system which is more highly developed than the posterior part, thus i t is more functionally important than the posterior part. The muscular wall of the posterior part of the digestive tract is very thin: tract us with long cilia probably move food. Because the caecal leaflets are not yet fully developed, the digestive gland probably assumes the gre atest part of the digestive and absorptive functions in paralarvae.