This is the first monograph to summarise data on the cyclomorphosis of heliolithids. The features of cyclomorphosis at intracolonial and population levels and within phylums are considered. The concept of phylum is elaborated. It is shown that changes in population growth rate could lead to the appearance of new taxa. The conditions under which recapitulations could be re-established have been elucidated. The difference between growth acceleration and accelerated development was explained. The question of the relationship between cyclomorphosis and the duration of phylum evolution has been considered. Data on cyclomorphosis of other groups of celenterates have been attracted. A considerable amount of references (110 in Russian and 63 foreign papers) and illustrations (37 figures) will give researchers a better understanding of the issues related to the study of coral cyclomorphosis. This work is intended for paleontologists and biologists interested in the morphology, evolution and systematics of Paleozoic corals and biorhythmology. It may also be of use to postgraduate and undergraduate biology students.