Live Invertebrates >> Cnidarians-Hydra

Hydra is a genus of simple, fresh-water animals possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa.

Hydras are low power microscopical life forms and are often studied by biologists due to their regenerative powers. They can be found in most un-polluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas.

Hydras are small animals with a body length ranging from 1 mm to 20 mm when fully extended. They have a tubular body secured by a simple adhesive foot. At the free end of the body is a mouth opening surrounded by a ring of 5 to 12 thin mobile tentacles. Each tentacle, or cnidae, is clothed with highly specialised stinging cells called cnidocytes. Cnidocytes contain specialized structures called nematocysts which look like miniature light bulbs with a coiled thread inside. At the narrow outer edge of the cnidocyte is a short trigger hair. Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release.