OBSERVATIONS ON PSEUDOCOLONIAL GROWTH IN HYDRA

¹ Department of Biology, Case Western Reserve University, Cleveland, Ohio 44106

1. Following a rise in culturing temperatures the reported strain of H. viridis grows in length and does not always detach its asexual reproductive products (buds). This aberrancy ultimately leads to the development of a pseudocolonial organization in these animals. Once elaborated, the pseudocolonial condition remains stable at normal culturing temperatures.

2. Analyses of several growth parameters in the pseudocolonial animals reveal that the normal role of the hypostome in the control of growth and form in hydra is modified in pseudocolonial individuals.

3. The principal morphological modification resulting from the altered hypostomal control is the absence of a peduncle region in the pseudocolonial hydra. Normal solitary hydra develop this histologically and histochemically distinct region immediately distal to the basal disc. Colonial hydroids, alternatively, possess no comparable region.

4. Comparing possible mechanisms for the control of growth and form in solitary, pseudocolonial, and colonial hydroids, the observations reported lead to the suggestion that there could be a morphological basis for colonial organization in the Cnidaria (i.e. the presence or absence of the capacity for peduncle formation).