The functional anatomy of the digestive tract of a shrimp Metapenaeus bennettae Racek & Dall (Crustacea : Decapoda : Penaeidae)

Abstract

The anatomy of the proventriculus, digestive gland, midgut and its diverticula, and the rectum is described. In structure and function the proventriculus is similar to that of anumber of other Decapoda. Two distinct cell types occur in the digestive gland, a secretory type, and a mucopolysaccharide-containing type, whose function is not clear. The digestive gland has no intrinsic muscles, and depends on extrinsic muscles, and possibly ingested water, for filling and emptying. The midgut extends to the sixth abdominal somite and faecal material is contained in a peritrophic membrane. Evidence for secretory functions of the midgut and anterior and posterior diverticula is discussed. The rectal lining is formed into six longitudinal pads which are used to expel long sections of peritrophic membrane containing faeces. Methods of feeding are described. Permeability of the anterior proventriculus to 22Na and [14C] glucose was measured; 22Na approached equilibrium in 6-7 hr, but [14C] glucose passed through at about one-seventh this rate, indicating that direct glucose uptake from the proventriculus would be negligible. Food, labelled with particulate ll0Ag, was found to begin leaving the proventriculus almost as soon as it was filled, but complete emptying took 6-12 hr. Defecation was at a peak 5-8 hr after food ingestion, but continued up to 20 hr. The rectum appears to have the additional function of pumping water into the gut via the anus.