TRANSEPIDERMAL ACCUMULATION OF NATURALLY OCCURRING AMINO ACIDS IN THE SAND DOLLAR,DENDRASTER EXCENTRICUS

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Abstract
The sand dollar D. excentricus is capable of net accumulation of amino acids found in the interstitial water of its sediment habitat. Influx and net flux of amino acids were measured radiometrically and fluorometrically. Rates of influx and net flux corresponded closely at ambient concentrations > 5 .mu.mol/l. Comparison of influx rates of naturally occurring primary amines with the metabolic requirements of animals as estimated from O2 consumption indicated that Dendraster could acquire sufficient reduced C to account for oxidative metabolism if its surface is exposed to the natural primary amines found in its environment provided concentration at the body surface .gtoreq. 35 .mu.mol/l. The primary amines in the interstitial water of sediment in the immediate vicinity of a shallow water population of Dendraster were ranged from 17-244 .mu.mol/l (115 .+-. 60; mean .+-. SD). Dendraster lives in an environment relatively rich in amino acids and possesses a transport system which can accumulate these compounds at rates sufficient to provide a major supplement to other forms of feeding. Sustenance of epidermal structures of echinoids and asteroids may be relatively independent of nutrient translocation from the digestive organs and may be based primarily on transepidermal influx of nutrients from the medium.