Hydra vulgaris Pallas, 1766, European freshwaters.
OTHER COMMON NAMES French: Hydre d'eau douce.
Solitary freshwater hydroids; 0.47 in (12 mm) in height; with 7-12 hollow filiform tentacles, but often moniliform distally, in one whorl under hypostome; hermaphrodic species, eggs and sperm developed directly in ectoderm of polyps in wart-like protuberances, "testis" developing on upper part of hydranth, "ovaries" on lower part, with up to eight eggs enveloped; in a chitinous embryotheca when fecundated, embryotheca with long, thin spines; asexual reproduction by lateral buds, leading only to temporary colonies; lower part of hydranth with simple pedal disc and with central pore, no perisarc except on encysted embryos.
Cosmopolitan. (Specific distribution map not available.) HABITAT
Freshwater surfaces, rivers, and ponds. BEHAVIOR
Fixed on freshwater plants, stones, empty freshwater shells, and worm larval tubes (Trichoptera); able to move with the help of the tentacles.
FEEDING ECOLOGY AND DIET
Feed on small freshwater planktonic organisms: primarily protozoa, rotifers, crustaceans, and worms.
Protanderic hermaphoditic; female sex cells fertilized when fixed on mother and enveloped in a chitinous spiny embryotheca.
CONSERVATION STATUS Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
Hydra is one of the most popular laboratory animals and has greatly contributed to the development of experimental biology. ♦
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