Question

Q:Define hydra...,!!!!​

Answer 1

Answer:

Hydra (/ˈhaɪdrə/ HY-drə) is a genus of small, fresh-water organisms of the phylum Cnidaria and class Hydrozoa. They are native to the temperate and tropical regions. Biologists are especially interested in Hydra because of their regenerative ability – they do not appear to die of old age, or to age at all.

Explanation:

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Answer 2

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$\dashrightarrow$Hydra is a genus of small, fresh-water organisms of the phylum Cnidaria and class Hydrozoa.

$\dashrightarrow$They are native to the temperate and tropical regions.

$\dashrightarrow$Biologists are especially interested in Hydra because of their regenerative ability – they do not appear to die of old age, or to age at all.

$\dashrightarrow$Hydra has a tubular, radially symmetric body up to 10 mm (0.39 in) long when extended, secured by a simple adhesive foot known as the basal disc.

$\dashrightarrow$Gland cells in the basal disc secrete a sticky fluid that accounts for its adhesive properties.

$\dashrightarrow$At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles.

$\dashrightarrow$Each tentacle, or cnida (plural: cnidae), is clothed with highly specialised stinging cells called cnidocytes.

$\dashrightarrow$Cnidocytes contain specialized structures called nematocysts, which look like miniature light bulbs with a coiled thread inside.

$\dashrightarrow$At the narrow outer edge of the cnidocyte is a short trigger hair called a cnidocil. Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release.

$\dashrightarrow$This can paralyze the prey, especially if many hundreds of nematocysts are fired.

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