NUTRIENT TRANSPORT IN STARFISH. I. PROPERTIES OF THE COELOMIC FLUID

¹ Department of Zoology, Cornell University, Ithaca, New York

1. A series of investigations was undertaken in an effort to clarify the role of the coelom and the coelomic fluid in the transport of nutrient substances throughout the body of starfish.

2. Serial chemical analyses of organic substances in the cell-free coelomic fluid of individuals did not reveal significant differences between fed specimens and those that had been starved for at least one week. The mean value of total nitrogen was 63.5 µg. N per ml., but large fluctuations occurred in all the specimens. Free ammonia was found to be present fairly constantly in the fluids, with a mean value of 12.8 µg. N per ml., or about 20% of the total nitrogen. Protein was determined to represent about 25% of the total nitrogen in two analyses. Reducing sugar occurred in the coelomic fluids in extremely low concentrations (mean value = 6.9 µg. per ml.) and showed moderate fluctuations in individual specimens.

3. Experiments in which starfish were fed C¹⁴-labeled algal protein hydrolysate, glucose, and palmitic acid showed that these substances were stored in the digestive glands and reached the other tissues only very slowly. Except possibly for palmitic acid, low levels of these nutrients occurred consistently in the coelomic fluid and coelomocytes at all times following feeding.

4. Experiments in which small amounts of C₁₄-labeled algal protein hydrolysate, glycine, and glucose were injected into the perivisceral coelom of starfish revealed that these substances are readily absorbed by the different tissues of the body, especially the digestive glands and, to a much lesser extent, the coelomocytes. An even greater proportion of glucose than the amino acids was taken up by the digestive glands.

5. These studies implicate the coelomic fluid as the most important medium of transport, and suggest that transport is accomplished as part of a continual flux of substances between the coelomic fluid and the various tissues of the body.