UTILIZATION OF DISSOLVED EXOGENOUS NUTRIENTS BY THE STARFISHES, ASTERIAS FORBESI AND HENRICIA SANGUINOLENTA

1. Small specimens of A. forbesi and H. sanguinolenta were exposed to dissolved C¹⁴-amino acids and glucose. The subsequent distribution of these materials was then determined in the following five regions of the body: disk (including the gonads), oral body wall of the rays, aboral body wall of the rays, stomach, and digestive glands. 2. In all cases, large proportions of the labeled nutrients were taken up into the external tissues. The largest amount was usually absorbed into the oral body wall, which probably possesses a proportionately greater ventilated surface area than the other regions. 3. Over a period of 20 days there was little indication of movement of the externally absorbed nutrients into the internal organs. In this period, very little loss of amino acid radioactivity was noted. The amino acids became progressively less soluable in alcohol, suggesting that they were incorporated into the structural proteins of the organism. 4. Glucose radioactivity declined progressively over the 20-day period. As observed in Asterias, this decline occurred almost exclusively in the portion of absorbed glucose that remained alcohol-soluble. This fraction was possibly used as an energy source while the insoluble fraction became incorporated into more inert elements. 5. A number of the specimens of Henricia appeared to pump up and absorb the glucose medium into their digestive organs. This was interpreted as a form of feeding behavior possibly initiated by the relatively high concentration of glucose used. The much less concentrated amino acid medium failed to initiate such a reaction. 6. It is concluded that nutrition in starfish is probably a dual process involving both a continuous epidermal absorption of dissolved exogenous materials for the benefit primarily of the superficial tissues, and intermittent oral feeding to satisfy the more general needs of the entire organism and especially of the internal organs.