Obelia

Obelia is a genus in the class Hydrozoa, which consists of mainly marine and some freshwater animal species and have both the polyp and medusa stages in their life cycle. The genus belongs to the phylum Cnidaria, which are all aquatic and mainly marine organisms that are relatively simple in structure.

Habitat

Obelia has a worldwide distribution except the high-arctic and Antarctic seas. The medusa stage of Obelia species are common in coastal and offshore plankton around the world.Obelia are usually found no deeper than 200 metres (660 ft) from the water's surface, growing in intertidal rockpools and at the extreme low water of spring tides. .

Life cycle

The polyp colony reproduces asexually. During this stage of life, Obelia are confined to substrate surfaces. On this mature colony there are individual hydranths called gastrozooids, which can be found expanded or contracted, to aid in the growth of this organism by feeding; the reproductive polyp gonozooids has medusa buds. Other hydranths are specialized for defense. The main stalky body of the colony is composed of a coenosarc, which is covered by a protective perisarc.