Modular organization of colonial hydroids is based on cyclic morphogenesis during growth of their body. In many thecate hydroids (Hydrozoa: Leptomedusae) the shoots of the colony consist of a few distinct elements and possess complex spatial organization. In most cases, the evolutionary sequence of morphogenetic modifications that led to present-day organization of shoots is obscure and not obvious. One of the approaches that allow getting insight into the morphogenetic evolution in colonial thecate hydroids is to analyse the spectrum of different minor morphotypes presented in the population of the certain species. In our opinion, some rare morphotypes allow understanding and reconstructing the scenario of morphogenetic evolution of species under consideration. We describe the application of such an approach for reconstruction of the morphogenetic evolution of Dynamena pumila (L.) (Sertulariidae) with some additional conclusions.
