Cyclomorphosis is seasonal polyphenism or the occurrence of seasonal changes in the phenotype of small aquatic invertebrate organisms that reproduce by parthenogenesis and can give rise to several generations annually, for example as rotifers and cladoceran crustaceans. The species of Daphnia for example, undergo the changes of the head's shape during the year, from midsummer to spring it has a round shape, and then it changes to a helmet-shaped, and again it reverting to the rounded shape at midsummer. Also some time in summer these generations tend to be smaller and more transparent than the other times. These changes are actually caused by the interaction of environmental change with the organisms genes, there by altering the course of development, the modifications are only associated with improved and survived organisms, by reducing the almost same type of predation.
Morphological variation in the population of Daphnia is been uncritically related to phenotype plasticity.The recent study discovered that the “cyclomorphic species” of Daphnia carinata was all together of nine species, many of these species often did sexual activity and seasonal change in their life cycle causes phenotypic cycles which are same as almost true cyclomorphosis. Specific genetic variation in head shape species also seems distributed in large number and is important in explaining phenotypic changes of many single species populations.
The helmet formation in daphnia is mainly related to predator avoidance but it is not supported by work on the D. carinata group. Natality differences exist between species with separate head size are suggesting that the helmet formation can cause direct effects on fitness. Two possibilities are mainly considered. This change may effect swimming efficiency because the length of the anterior adductor muscle is directly correlated with helmet size .In addition the laminar design of helmets suggests a role in gas exchange.
Cyclomorphosis in Rotifers:-
Many pelagic species undergo seasonal changes in body shape or structures like length of specific appendages or the body size in the clone line of a pathogenetically reproducing organisms., a phenomenon known as cyclomorphosis.
Cyclomorphosis is a change that occurs seasonally in the rotifers,because of the seasonal change temparature change is usually play a important role as one of the major causative factors . Food supply, ph effects, and the influence of the female principle were also investigeted. But in the case of rotifera however the situation is still unclear, because some certain rotifer species react to temperature in the same manner as the cladocera. Other species reactions seems to differ considerably in this situation.