Experimental studies on the seasonal variation of the rotifer Keratella cochlearis (Gosse)

A culture containing the rotifer Keratella cochlearis was divided into two aliquots, one reared at + 20°C and the second at + 5°C, all other conditions being identical. The experimentl lasted 74 days. At 20°C the animals did not undergo any noticeable morphological changes, while at 5°C the posterior spines grew longer, a development which had nearly reached its maximum as early as 30 days after the experiment began, i.e. after very few generations. The experiment shows that the temperature (and its direct consequences, such as slower growth) plays an important role in causing seasonal morphological variation in this rotifer. The results are in accordance with field experience as well as with culture experiments on other brachionid rotifers.