JAECKLE, W.*; SLOTT, A.; BALSER, E.; Ill. Wesleyan U., Bloomington; Ill. Wesleyan U., Bloomington; Ill. Wesleyan U., Bloomington: Patterns of nutrient assimilation and distribution in tornaria larvae.
Although the mechanism of particle capture is known for tornaria larvae (Hemichordata: Enteropneusta), the sites of material absorption and patterns of material distribution within the larval body are unresolved. Many mature tornariae develop a voluminous blastocoelic space where the epithelium of the digestive system and the outer epithelium are separated by distances of 1+ mm. We report here the results of experiments designed to evaluate the ability of the outer epithelium and the digestive system to assimilate macromolecules from seawater and to trace the movement of a label within the larval body. Tornaria larvae, collected from plankton tows taken in the western Atlantic and eastern Pacific Oceans, were incubated in solutions of the protein ferritin and the polysaccharide iron dextran (50 kD ea., 1-2 mg / ml) for varying times. After each incubation period, the iron label associated with each macromolecule was visualized in larval cells after performing the �Prussian Blue� reaction. For larvae exposed to ferritin, to date we have been unable to detect the reaction product in cells of the digestive system or the outer epithelium. We have, however, consistently identified the label in the cells of the protocoel and pore canal and in mesenchyme cells within the blastocoel. In contrast, larvae exposed to iron dextran only revealed the label within basal portions of the gastric and intestinal epithelia. Although there was no intracellular label in cells of the protocoel and pore canal, iron dextran was adsorbed to the apical surfaces of these cells. Control specimens never revealed any reaction product. These results indicate that the direction of fluid flux in tornaria larvae may be bidirectional along pore canal and the dorsal pore may serve as both an entrance and exit for fluid into and out of the larval blastocoel.
