Hydra

From Wikinfo

Hydra species

Kingdom:	Metazoa
Phylum:	Cnidaria
Class:	Hydrozoa
Order:	Hydroida
Family:	Hydridae
Genus:	Hydra
Species:	sp.

Binomial name

Hydra sp.

Zoology

Hydra is the name of a simple fresh-water animal. Found in the phylum Cnidaria, of the class Hydrozoa. Hydras are radial in symmetry. Cnidocytes are unique cells used by hydras to make nematocytes. Nematocytes are stinging capsules that look like light bulbs with a wiggling string coming out of the middle. Nematocytes make an electrical discharge that is used to paralyze their prey. Hydras have an integument made of mesoglea, a gel like substance. The integument is made of an outer epidermis and internal gastrodermis that are separate from the other. The colelentron is in the middle of the gastrovascular cavity and is the place where the digestion process occurs. They have tenticles where the cnidocytes are held. Hydras go through a body change from polyp to an adult form called medusa. Hydras have a nerve net for a nervous system which is primitive compared to mammalian nervous systems as they do not have a brain. Nerve nets are connecting sensory photoreceptor nerve cells that are found in the body wall of hydras. Photoreceptors detect light and send signals to the body.

Species of Hydra

Chlorohydra viridissima
Hydra attenuata
Hydra cf. oligactis
Hydra circumcincta
Hydra littoralis
Hydra magnipapillata
Hydra oligactis
Hydra sp.

References

Gilberson, Lance, Zoology Lab Manual 4th edition. Primis Custom Publishing. 1999
Solomon, E., Berg, l., Martin, D., Biology 6th edition. Brooks/Cole Publishing 2002