Ontogeny of gut morphology in the white shrimp Penaeus setiferus (Decapoda, Penaeidae).

Abstract

Ontogeny of the gut in Penaeus setiferus was investigated by reconstruction of serial sections examined by light microscopy. Development of the gut into the adult form is protracted over several weeks beyond metamorphosis in steps that may be directly related to the unique postlarval life history of Penaeus. The gastric mill is lacking in larval stages of P. setiferus. In protozoeal stages Z1 -Z3 , the pyloric ampullae are blind sacs that do not communicate with the midgut. The gland filter first appears in mysis stage M2 . The gastric mill in early postlarval (PL) stages consists of poorly chitinized lobes with flexible setae. By PL21 the ossicles of the gastric mill are rigid and setae are replaced by spine-like denticles, but even by PL35 the gastric mill is neither as massive nor heavily chitinized as in adults. During the mysis stages and early PL stages, the hepatopancreas communicates freely with both the foregut and the midgut trunk. By PL35 the hepatopancreatic ducts are essentially isolated from the remainder of the midgut by foregut ossicles. The midgut in Z1 consists of two pairs of simple caeca and the midgut trunk. During larval growth, each of the lateral midgut caeca develops into a number of lobes. After metamorphosis these lobes begin to ramify into small-diameter tubules, and by PL35 have completely ramified into the hepatopancreas of adults. From M1 to PL4 , the anterior midgut caeca decrease in absolute size and become a single anterior diverticulum. The posterior midgut diverticulum first appears in PL21 as a simple sac and thereafter increases in size and complexity.