Das marine, stockbildende Hydrozoon wächst auf Schneckengehäusen, die von Einsiedlerkrebsen bewohnt sind. Nähr-, Geschlechts-, Tentakel- und Wehrpolypen und ihre Funktionen; entodermales Kanalsystem der Stoffverteilung als Kommunikationssystem des Stockes. Nahrungstransport durch peristaltische Pulsationen.

The colony of the marine hydroid Hydractinia echinata grows symbiontically on shells of hermit crabs. It develops four types of hydranths: gastrozooids, gonozooids, spiralzooids, tentaculozooids. These polyps and their main behavioural reactions are demonstrated. The hydranths represents "organs" of a suprapersonal individual, that is the whole colony, and are interconnected by a system of endodermal channels through which fluid and food are distributed. Pulsations of the hydranths and of the stolonial endodermal tubes provide forces for the transport.