NUTRIENT TRANSLOCATION IN THE SEA STAR: WHOLE-BODY AND MICROAUTORADIOGRAPHY AFTER INGESTION OF RADIOLABELED LEUCINE AND PALMITIC ACID.

Using the sea star, Asterias rubens, whole-body autoradiography has been employed to follow the distribution and the pathways of translocation of both soluble and tissue-incorporated label derived from orally administered 14C-labeled leucine or palmitic acid. Radioactivity remains localized predominantly in the stomach and pyloric caeca until sixteen days after ingestion. Labeling of the perivisceral coelomic cavity in regions close to the stomach shortly after ingestion points to initial displacement of ingested nutrients through the coelomic fluid and coelomocytes. After oral administration of labeled palmitic acid, distinct labeling of the gastric hemal tufts, axial organ, and aboral ring prior to labeling of the gonads also suggests the involvement of hemal tissue and surrounding perihemal coelomic sinuses in storage and translocation of substances needed for gamete nutrition. Microautoradiography of gonad tissue reveals a rapid labeling of the walls of the genital coelomic sinus, the ground substance of the genital hemal sinus, and, after prolonged incubation, the germinal epithelium. Little or no label is incorporated into the outer sac of the gonad wall. The results are discussed in terms of current knowledge on nutrient translocation in the sea star.