Hydra (biology)
Hydra americana
Hydra attenuata
Hydra canadensis
Hydra carnea
Hydra cauliculata
Hydra circumcincta
Hydra hymanae
Hydra littoralis
Hydra magnipapillata
Hydra minima
Hydra oligactis
Hydra oregona
Hydra pseudoligactis
Hydra rutgerensis
Hydra utahensis
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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.
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
