SURVIVAL AND MOVEMENTS OF THE FLATWORM, STYLOCHUS ELLIPTICUS, IN DIFFERENT SALINITIES AND TEMPERATURES

¹ U. S. Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut

1. Stylochus ellipticus from Milford Harbor, Connecticut, survived abrupt transfer from a salinity of about 27 ppt to salinities as low as 7.5 ppt at room temperature. Those transferred directly to 5 ppt suffered a mortality of 20% but all worms died when placed directly in 2.5 ppt and fresh water. However, worms that acclimated to 5 ppt survived subsequent transfer to 2.5 ppt.

2. Righting time of S. ellipticus at room temperature remained constant at 12 to 15 seconds in salinities ranging from about 27 ppt to 7.5 ppt but increased to 22 seconds in 5 ppt and to 37 seconds in 2.5 ppt.

3. Righting time of S. ellipticus in a salinity of about 27 ppt was approximately 8 seconds at temperatures of 20°, 25° and 30° C., 16 seconds at 12.5°, 15° and 17.5° C., 30 seconds at 10° C. and 116 seconds at 7.5° C.

4. Locomotion rate of S. ellipticus varied erratically with temperature but generally decreased with temperature decreases below 20° C. It exceeded 50 millimeters per minute at temperatures of 20° C. and higher but decreased to 10 mm./min. at 7.5° C.

5. At the same temperatures S. ellipticus from Milford Harbor moved faster than reported for the same species from Apalachicola Bay, Florida. This observation suggests that there may be physiological races within this species of flatworm.

6. When temperature and salinity were lowered simultaneously righting time of S. ellipticus was frequently longer than the combined righting times obtained when the two factors were observed separately.