hydra

In zoology, any of a group of freshwater polyps, belonging among the coelenterates. The body is a double-layered tube (with six to ten hollow tentacles around the mouth), 1.25 cm/0.5 in long when extended, but capable of contracting to a small knob. Usually fixed to waterweed, hydras feed on minute animals that are caught and paralysed by stinging cells on the tentacles. (Genus Hydra, family Hydridae, phylum Coelenterata, subphylum Cnidaria.)

Hydras reproduce asexually in the summer and sexually in the winter. They have no specialized organs except those of reproduction.

Hydra

In astronomy, the largest constellation, winding across more than a quarter of the sky between Cancer and Libra in the southern hemisphere. Hydra is named after the multi-headed sea serpent slain by Hercules. Despite its size, it is not prominent; its brightest star is second-magnitude Alphard.

It is sometimes identified as the River Nile or Jordan, but is more usually represented as a snake trailing along the ground bearing on its back a cup (Crater) and near its tail a seated crow or raven (Corvus).

Hydra

In Greek mythology, a huge monster with nine heads. If one were cut off, two would grow in its place. One of the 12 labours of Heracles was to kill it.