Distribution:- Obelia found from arctic region to the Gulf of Mexico and the pacific coast and from southern California to Oregan.
Habit and Habitat:- Obelia is a colonial, marine sedentray hydrozoan zoophyte found attached on piles , rocks and seaweeds in shallow water.
1) Obelia is a colony.
2) The colony consists of a basal horizontal portion, the hydrorhiza which is attached with the substratum and a number of vertical branches known as hydrocauli.
3) The hydrorhiza and hydrocauli are covered by a chitinous perisarc which encloses soft inner coenosarc.
4) The colony is trimorphic having three types of zoids, e.g hydranth, blastostyle and medusa.
5) Blastostyle zooild in club-shaped without mouth and tentacles.
6) Medusa is bell shaped with a concave and a convex side.
1) Obelia is used in many zoology textbooks to exemplify the Hydrozoa Life Cycle.
2) Obelia is useful for laboratory research.
3) Museum specimen.
4) Nematocysts can penetrate human skin.
COMMENT OF Medusa of Obelia
Distribution:- It is cosmopolitan in distribution world wide except the high-arctic and Antarctic sea.
Habit and Habitat
Obelia is a sedentary, marine form found attached on the surface of sea weeds, molluscan shell, rocks and wooden piles in shallow water up to 80 meters in depth.
1) The medusa of obelia is umbrella-like in shape.
2) The rim of the umbrella is fringed with numerous tentacles carrying nematoblasts.
3) Manubrium is hanging down from the subumbrella surface and bearing the mouth opening at its free end.
4) The gastric cavity branches into four radial canals and these join at their distal ends into circular canals.
5) Radial symmetry is well defined in medusa.