DIGESTIVE ENZYMES IN PARALARVAL CEPHALOPODS

Fourteen enzymes involved in digestion (esterases, glycosidases and pe ptidases) were localized by histochemical methods in planktonic parala rvae belonging to four families of cephalopods: Octopodidae, Bolitaeni dae (Octopods), Ommastrephidae and Enoploteuthidae (Oegopsid squids). The high protease activity and very low or histochemically undetectabl e amylasic activity indicate a carnivorous diet suggesting that the di et of paralarvae resembles that of adults. The digestive gland display s the highest enzyme activities which agrees with the key role of the gland in the digestive processes of cephalopods. In particular, the gl and appears to be the main source of the proteolytic enzymes found in the posterior digestive tract. The high acid phosphatase activity, DAP II and acetyl-glycosaminidase activities, typically lysosomal, point to intracellular digestive processes in the gland. The posterior saliv ary glands are as well developed in squids as in octopods and they dis play several enzyme activities, most notably a high proteolytic activi ty. This could indicate that the salivary glands would be more involve d in the digestive processes in paralarval squids than in adults where they are mostly poison glands. In all of the specimens studied, the w hole digestive system appears to be already developed and able to dige st prey. The high level of alkaline phosphatase activity of the skin s uggests active exchanges with the external medium. It seems possible t herefore that nutrients could be absorbed through the skin and provide a part of the energy necessary to the young cephalopods.