Hydroid (Campanularia flexuosa). Light micrograph (LM) of a colonial hydroid, showing gonozooid (reproducing) and gastrozooid (feeding) polyps, attached to a central stolon (stalk). This hydroid is commonly found growing on seaweed in the inter-tidal zone of the seashore. Hydroid is a collective name for a colony of individuals (polyps). A division of labour exists within the colony: the feeding polyps are cup-shaped and are surrounded by retractable tentacles with stinging cells that catch small prey, and the club-shaped reproductive polyps produce medusae, comparable to little jellyfish. The medusae produce eggs and sperm into the seawater where fertilisation takes place.