Cylindrical body is tube-like measuring approximately 1.3· cm in length.
Anterior end contains mouth or hypostome, which is crowned with 6 to 10 filiform nematocyst bearing tentacles.
Proximal end of the body contains pedal or basal disc or foot meant for attachment to the substratum.
Body is diploblastic, consisting of outer ectoderm, inner endoderm and intervening mesogloea. Body wall encloses a gastrovascular cavity extending into the tentacles.
In female Hydra ovary and buds are found on sides in mid position.
In male Hydra 3 or 4 pairs of testes are found anteriorly and a full grown bud with tentacles on side.
Testes develop near the oral end and ovaries near the base.
It reproduces sexually by fusion of sperms and ova.
During asexual reproduction, lateral buds develop on the sides of the body which later on detach and develop into new Hydra.

SPECIAL FEATURES

Hydra viridis contains symbiotic green algae Zoochlorellae. Hydra is famous for division of labour for the first time in animal kingdom and moreover it has great experimental value as most of the regeneration and grafting experiments are conducted on it.

IDENTIFICATION

Since the animal contains 6-10 filliform tentacles anteriorly and gonads and buds on side and all above characters and hence it is Hydra. Male Hydra has 3 to 4 pairs of testes near oral end.