Morphogenetic Polyvariance in the Colonial Hydroid Dynamena pumila (L.)

Abstract

The formation of aberrant modules (internodes) of the shoot was found sporadically in the colonial hydroid Dynamena pumila from the family Sertulariidae, which is distinguished by the symmetrical two-row position of the hydrotheca on the shoot stem. Despite rare significant deviations from the norm in the structure of some modules, the following modules in the shoots are formed normally. All variants of deviation from the norm (called morphovariations) are classified and, in general, are represented by four groups according to the possible reasons for their occurrence. The morphotypes are the most interesting morphological variations and look like similar modules in other genera of hydroids. Considering the position of the aberrant modules on the shoots of one colony, we can confidently infer that they were formed at different times, which undermines the assumption that deviations from the norm in morphogenesis were caused by environmental factors. All morphovariations are characterized by certain occurrences. Consequently, the described phenomenon is not limited to phenotypic plasticity, polymorphism, or sequential changes of phenotypes in the life cycle and, therefore, is singled out as a special phenomenon called morphogenetic polyvariance.