FLUID EXTRACTION AND CIRCULATION IN THE PROVENTRICULUS OF THE BANANA PRAWN PENAEUS MERGUIENSIS DE MAN

ABSTRACT The morphology and gastric armature of the proventriculus of Penaeus merguiensis closely resembles that of predominantly macrophagous decapods. Two modes of gastric mill operation were observed, chewing and compression. Gastric mill activity typically began with several ventral compressions of the ossicles above the lateral teeth. This was followed by a single anterior chewing movement of the median tooth in conjunction with a shearing medial movement of the lateral teeth. Morphological examination and observations of fluid movements within the proventriculus of live specimens have added to a previous model of proventricular circulation. Fluids are drawn ventrally from the cardiac stomach through two filters, of which the first is coarser than the second. The gaps between the setules of the filter setae in the secondary filter indicate that only particles in the colloidal size range or smaller can enter the digestive gland. Fluids are removed from the digestive gland and pulled anteriorly through fully enclosed passageways to return to the cardiac stomach. This action is the result of suction created behind the median tooth as it swings anteriorly during normal gastric mill activity. The return of fluid to the cardiac stomach completes the circulation of proventricular fluids and would allow enzymes from the digestive gland to begin food digestion soon after it has been ingested.