Virginia Institute of Marine Science
The tissues of marine invertebrates contain very high levels of free amino acids (FAA) which are believed to serve an intracellular osmoregulatory function (e.g., Fiorkin and Schoeffeniels, 1965 ) . Potts ( 1967) suggested that as a consequence of these high FAA levels and the tendency of these compounds to leak across the body wall into the water, marine invertebrates probably lose more FAA to the water than do comparable freshwater invertebrates. Consistent with this hypothesis was our observation that both tissue FAA levels and FAA release rates of the marine turbehlarian, Bdelloura candida increased with increasing salinity (Johannes, Cow ard and Webb, 1969). Relative respiratory costs of coping with mi-marine versus freshwater emiviron ments have been calculated ( Potts, 1954 ; Potts and Parry, 1964) . If differences in FAA release rates between marine and freshwater invertebrates exist as a con sequence of differences in tissue FAA levels, this implies another type of differential energy loss related to osmoregulation one iii which studies of the respiratory energy costs of osmoregulation do not take into account. Here we compare FAA release rates of Bdelloura and its freshwater relative (Dugesia dorotocephala ) , on an energetic basis.
Contribution (Virginia Institute of Marine Science) no. 390.
Webb, Kenneth L.; Johannes, R. E.; and Coward, S. J., Effects of salinity and starvation on release of dissolved free amino acids by Dugesia dorotocephala and Bdelloura candida (Platyhelminthes, Turbellaria) (1971). Biological Bulletin, 141, 364-371.