The digestive system of rhynchoteuthion paralarvae (Cephalopoda: Ommastrephidae)

The anatomy of the digestive system and the digestive system enzymes of three types of rhynchoteuthion paralarvae A′, B′, and C′ (Illex) were studied. No differences among the three were found. The main features of the digestive system of these species of paralarval Ommastrephidae are described. The buccal mass is comprised of a beak and radula with conspicuous teeth. The well developed posterior salivary glands contain glandular tissue with two cell types: A, goblet cell, and B, granular cell. The esophagus is lined with a thin cuticle, but the stomach lacks cuticle and has a more strongly developed muscular wall than the esophagus. The large vestibule is lined with ciliated and glandular cells. Some primary folds of ciliated epithelial cells begin to develop in the caecum. The digestive gland is compact, round, red-pigmented and enclosed in a thick elastic capsule; it contains conspicuous inclusions: large boules, typical brown-body vacuoles and numerous lipid droplets. Thirteen hydrolases involved in digestive processes were examined. High proteasic activity and histochemically undetectable amylasic activity suggest a carnivorous diet. The occurrence of typical lysosomal enzymes in the digestive gland reveals a high intracellular digestive activity. The digestive system appeared to be developed and functional 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 it is more functionally important than the posterior part. The muscular wall of the posterior part of the digestive tract is very thin: tractus with long cilia probably move food. Because the caecal leaflets are not yet fully developed, the digestive gland probably assumes the greatest part of the digestive and absorptive functions in paralarvae