Meeting Abstract

P3.116  Friday, Jan. 6  Uptake of dissolved high molecular weight molecules by larvae of Lytechinus variegatus MCDONALD, A.J.*; JAECKLE, W.B.; Illinois Wesleyan Univ., Bloomington; Illinois Wesleyan Univ., Bloomington

Echinoid larvae can absorb small and large dissolved organic materials (DOM) from seawater (e.g., amino acids and proteins, respectively). DOM uptake is normally attributed to ectodermal epithelia, but uptake by the digestive tract has been reported. Protein uptake by larvae has been observed in the endodermal epithelium. These observations suggest seawater flows through the larval digestive system and that the digestive epithelium can remove DOM from this flow. To test this hypothesis we exposed pluteus larvae of the sea urchin Lytechinus variegatus to concentrations of polysaccharides and proteins that reflect their abundance in seawater. Pluteus larvae of varying ages were incubated in filtered seawater containing 264 nM solutions of polysaccharides (rhodamine-dextran, iron dextran) and proteins (FITC-albumin, ferritin) for 1 to 4.5 h. Labeled dextrans were assimilated only by the cells of the larval stomach; rhodamine-dextran was detected in gastric cells after a 1-h exposure. In contrast, labeled albumin was present in cells of the ectodermal ciliary band, the entire gut lining, and the distal end of the pore canal after exposures of 1-h. Ferritin uptake was detected in cells of the stomach and the distal end of the pore canal after 4-h exposures. The assimilation of macromolecular DOM from seawater by the digestive epithelium suggests a flow of water through the gut. The presence of labeled cells at the pore canal terminus is also suggestive of an influx of seawater, but we cannot exclude resorption of the label from primary urine formed by the “larval kidney”. Uptake of proteins by outer epithelium was only seen in cells of the larval locomotory structure. That pluteus larvae can take up both low and high molecular weight forms of DOM suggests that DOM may be a significant nutritional resource.