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SUMMARY
The uptake of dissolved organic matter by the whelk Bullia digitalis has been monitored using a mixture of radioactive amino acids. Efflux as well as influx was measured and attention paid to the sites of uptake, which proved to include the surface of the foot as well as the gill. A net rate of amino acid influx of over 1 x 10−3μg hr−1 was calculated for a standard animal of 750 mg dry tissue mass, from a solution of just over 1 μg ℓ−1. It is concluded that, under natural conditions, utilization of dissolved amino acids and other dissolved organic matter could account for a fairly high proportion, certainly more than 15 per cent, of the metabolic needs of the animal and may be essential as a nutrient source for young juveniles.