COMPARISON OF THE LEVEL OF CHLORIDE REGULATION BY NEREIS DIVERSICOLOR IN DIFFERENT PARTS OF ITS GEOGRAPHICAL RANGE

¹ Department of Zollogy, University of California, Berkeley 4, Calif.

1. Laboratory studies have been made of the level of chloride regulation in Neresis diversicolor from representative parts of its geographical and ecological range. Areas studied include marine-dominated habitats in Scotland and southern England, estuarine habitats in southern England, conditions of low salinity in the Gulf of Finland, and intermediate salinities in the Isefjord, Denmark.

2. Animals have been adapted from their environmental salinity to a series of salinities from full sea water or higher down to fresh water, and the chloride level of the coelomic fluid has been determined after full adaptation and feeding at each salinity.

3. Results indicate that N. diversicolor as a species shows a uniform pattern and level of chloride regulation regardless of the region in which it is found. The test does not demonstrate physiological races differing in respect to salinity tolerance, although the possibility that other criteria may prove diagnostic of such races is not ruled out.

4. It is suggested that the assumption of the existence of physiological races in N. diversicolor should only be made after analysis of the environmental factors in question, and that certain differences of response and distribution may be caused by environmental rather than racial factors. For instance, the failure of N. diversicolor to populate oligohaline waters in Finland seems to be the result of local seasonal hydrographic factors rather than to indicate a physiologically distinct race of the species in that area.