Symmetry in colonies of thecate hydroids (Cnidaria, Hydroidomedusa, Leptomedusae): Transition from radial to bilateral symmetry

Abstract

Hydroid polyps (Cnidaria, Hydrozoa) are characterized by predominantly radial symmetry. On the basis of the Berking’s model (Berking 2003, 2006), which is based on the positional information and “self-activation and lateral inhibition” hypotheses, transition from radial symmetry of the primary module to bilateral symmetry or glide-reflection symmetry of compound shoots of thecate hydroids (subclass Leptomedusae) is analyzed. It is shown that ordering of three-dimensional structure and changes in the symmetry type are byproduct of mechanisms regulating the developemnt of modular organisms based on the cyclic morphogenesis.