hydra (redirected from hydrae)

hydra, in zoology

hydra (hī`drə), common name for freshwater organisms in the phylum Cnidaria, which includes jellyfish, sea anemones, and corals. Hydras are widely distributed in lakes, ponds, and sluggish streams. They are small, cylindrical, solitary organisms, the largest reaching about 1 in. (2.5 cm) in length. They attach themselves temporarily to water plants or submerged objects, using an adhesive pedal disk at the anal end. The simple body consists of an outer layer of epidermis, a middle noncellular layer of mesoglea, and an inner layer of gastrodermis lining the simple gastrovascular cavity, where the final stages of food digestion occur. A whorl of tentacles surrounds the mouth. Hydras feed on small plankton organisms, especially microcrustaceans, stunning them with stinging cells (nematocysts) in the tentacles. Hydras reproduce asexually by budding and sexually by means of gonadal cells formed on the sides of the body. The green hydra, Chlorhydra viridissima, contains green algae living symbiotically in its gastrodermal cells. The gray and brown hydras belong to the genus Pelmatohydra. Several species of hydra also occur in American waters. Hydras are classified in the phylum Cnidaria, class Hydrazoa.

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Hydra, in astronomy

Hydra, in astronomy, southern constellation lying S of Corvus, Crater, Virgo, Leo, and Cancer. It is a long, slender, winding constellation traditionally depicted as a snake and known also as the Water Monster or Sea Serpent. The only bright star in the constellation is Alphard (Alpha Hydrae); it is a double star, but the two components can be detected only with a telescope. Hydra reaches its highest point in the evening sky in the spring.

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Hydra, in Greek mythology

Hydra, in Greek mythology, many-headed water serpent; offspring of Typhon and Echidna. When one of its heads was cut off, two new heads appeared. The second labor of Hercules was to kill the monster. He did so by burning the neck after cutting off each head.

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Hydra, island, Greece

Hydra, Greece: see Ídhra.

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hydra

Any of 20–30 species of freshwater cnidarians (genus Hydra). The polyp-type body is a thin, usually translucent tube that measures up to slightly more than 1 in. (25 mm) long. Food is ingested and wastes are ejected from the open, tentacled end. Individuals are usually hermaphroditic (see hermaphroditism). Reproduction by budding is also common. Species differ in colour, tentacle length and number, and gonad position and size. All hydras feed on other small invertebrates (e.g., crustaceans).

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HYDRA

(1) A secure Web server from Sentinel Systems, formerly Bodacion Technologies, Barrington, IL (www.bodacion.com). Sentinel is a wholly owned company of the Centuria Corporation, www.centuria.us.

HYDRA is a virus-proof, hacker-proof PowerPC-based system that uses a proprietary operating system kernel for running Java servlets and JSPs. Applications programmed in the company's own Genesis language can be compiled on Windows and Unix workstations and then uploaded. As an extra step in foiling hackers who insert bogus packets into the data stream, HYDRA includes software that generates extremely random numbers called "Bodacions." Applications can use Bodacions to generate numbers such as account numbers, session IDs and TCP sequence numbers.

(2) (Hydra) The code name for Windows Terminal Server. See Windows Terminal Server.

(3) (HYbrid Document Reproduction Apparatus) A printer, photocopier, scanner and fax built into one machine.

(4) (Hydra) A device that converts analog signals to ISDN Basic Rate Interface (BRI).

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hydra

any solitary freshwater hydroid coelenterate of the genus Hydra, in which the body is a slender polyp with tentacles around the mouth

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hydra [′hī·drə]

(invertebrate zoology)

Any species ofHydraor related genera, consisting of a simple, tubular body with a mouth at one end surrounded by tentacles, and a foot at the other end for attachment.

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Hydra [′hī·drə]

(astronomy)

A large constellation of the Southern Hemisphere, right ascension 10 hours, declination 20° south. Also known as Water Monster.

(invertebrate zoology)

A common genus of cnidarians in the suborder Anthomedusae.

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Hydra

nine-headed serpent beheaded by Heracles. [Gk. Myth.: Benét, 489]

See : Decapitation

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Hydra

seven-headed water snake; ravaged Lerna, near Argos. [Gk. and Rom. Myth.: Hall, 149]

See : Monsters