ABSTRACT
This chapter discusses the mechanisms involved in the absorption of soluble organic nutrients, both by coelomocytes and by the plasma membrane of specialized absorptive cells. A similar mechanism was proposed by Enriques for intestinal transport of nutrients in holothuroids, in an attempt to explain absorption across an alimentary epithelium which was apparently impermeable to a number of organic and inorganic solutes. An a priori consideration of the source of nutrient molecules and their site of absorption in the echinoderms would suggest that, like other free-living metazoans which have evolved complex alimentary systems, soluble digestion products would be absorbed via epithelial cells lining the alimentary canal. The hypothesis that coelomocytes are involved in the absorption of nutrients is based on the circumstantial evidence that coelomocytes associated with the gut ingest foreign inert material from the lumen and then traverse the alimentary wall.
