Phylum - Cnidaria
Habit and Habitat: Many members of this phylum live in worldwide in freshwater, drain, canal, river, lake, stream etc. But maximum are marine species. They are of different colour, shapes and sizes; they are the beauty of sea they are attached with floating wood, leaves or something else or free swimming.
Some species are free living and some are colonial. As: Hydra (fresh water animal) Jelly fish (Marine water animal) and Corals (Marine).
a) They are two layered animals; body is formed of two embryonic celllayers ectoderm and endoderm. Between these two layers there is a non-cellular layer called mesoglea.
b) A body cavity named coelenteron or gastrovascular cavity takes part both in digestion and water circulation.
c) In the ectoderm there are specialized cnidoblast cells. Example: Hydra
Example : Hydra vulgaris, Aurelia aurita.