Where to hydra and other cnidarians live?

Answer 1

Hydra is a genus of simple, fresh-water animals possessing bilateral symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas. They are usually a few millimeters long and are best studied with a microscope. Biologists are especially interested in hydras due to their regenerative ability. Hydras appear to be unique among animals in that they do not undergo senescence (aging).

Hydra is a small animal with a body length ranging from 1 mm to 20 mm when fully extended. It has a tubular body secured by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that allows for its adhesive properties. At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles. Each tentacle, or cnida (plural: 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. To humans, this poses a nuisance at worst; however, to some prey, this strike can be paralyzing.

Hydras mainly feed on small aquatic invertebrates such as Daphnia and Cyclops. All species of Hydra exist in a mutual relationship with various types of unicellular algae. The Hydra affords the algae protection from predators and in return, phoyosynthetic products from the algae are beneficial as a food source to the 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. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas. They are usually a few millimeters long and are best studied with a microscope. Biologists are especially interested in hydras due to their regenerative ability. Hydras appear to be unique among animals in that they do not undergo senescence (aging).

Hydra is a small animal with a body length ranging from 1 mm to 20 mm when fully extended. It has a tubular body secured by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that allows for its adhesive properties. At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles. Each tentacle, or cnida (plural: 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. To humans, this poses a nuisance at worst; however, to some prey, this strike can be paralyzing.

Hydras mainly feed on small aquatic invertebrates such as Daphnia and Cyclops. All species of Hydra exist in a mutual relationship with various types of unicellular algae. The Hydra affords the algae protection from predators and in return, phoyosynthetic products from the algae are beneficial as a food source to the Hydra .

Answer 2

Hydra live attached to vegetation by the base of the tubular body or column, with their tentacles suspended free in the water. At the base of the tentacles is the mouth. Smaller animals which blunder into the tentacles are stung and paralyzed and drawn into the mouth. Most species of hydra are less than 0.6 inches (15 mm) in length, not including the tentacles, and are inconspicuous. Both column and tentacles are highly contractile and, by expelling gastrovascular fluid from the mouth, a hydra can shrink to a fraction of its previous volume. Hydra will only rarely be spotted in their natural habitats, but if samples of aquatic vegetation are transferred to a clear glass or plastic container, they will often be found in considerable numbers. Both the column and tentacles gradually extend in still water.

Several species of hydra have been recorded in the Great Plains, but most are difficult to identify without detailed microscopy. Two species, however, are distinctive. Hydra (Chlorohydra) viridissima (green hydra) is a bright green species, owing to the presence of numerous algae called zoochlorellae, which live as symbionts within the endodermal cells.The zoochlorellae carry out photosynthesis and produce sugars that are used by the hydra. In return, the carnivorous diet of the hydra provides a source of nitrogen for the algae. Green hydra are small, seldom more than 0.4 inches (10 mm) long, with tentacles about half the length of the column.

Hydra oligactis is easily distinguished from other hydra by its very long tentacles, which may extend to 2 inches (5 cm) or more when relaxed. The column is a pale translucent brown, 0.6 to 1 inch (15 to 25 mm) in length, with the base distinctly narrowed to form a "stem" or "foot."

Hydra vulgaris and H. braueri have been grouped as a "species clusters" by Campbell (1987), and each probably contains several true species. Classification depends on the structure of the eggs and stinging cells (see below). All of these species have tentacles that are similar in length to the column or somewhat shorter. The color is pale translucent brown or gray. None possesses the basal narrowing of the column seen in H. oligactis . This group includes animals that are 0.2 to 0.6 inches (5 to 15 mm) in length.

Hydra oligactis and Chlorohydra viridissima are both widespread and common in South Dakota in still and slow-flowing

freshwater habitats. Members of the H. vulgaris and H. braueri complexes may also be encountered. Unlike many freshwater

animals, hydra tolerate considerable eutrophication, which is a problem in many state waterways owing to intensive agriculture. They are also tolerant of wide temperature fluctuations, although most of our species probably over-winter as dormant eggs. I have found hydra in saline lakes with salinities up to 40 milliosmoles (approximately 1%) but they probably do not occur in salinities much higher than this. These broad ecological tolerances make hydra widespread and common, although they are sensitive to heavy metal toxicity.

Natural History

Hydra are sessile and live attached to aquatic vegetation, submerged twigs or rocks. They are frequently found on the floating leaves and suspended roots of duckweed, Lemna spp. Attachment is accomplished by mucous secretions from the basal disc. Although hydra remain stationary for long periods, they may move considerable distances by bending the column, attaching with the tentacles, releasing the basal disc, then flipping the column over and re-attaching. This behavior is termed somersaulting.

Prey are paralyzed by neurotoxins released from tiny stinging organelles , called cnidae or nematocysts. The cnidae are formed within the ectodermal cells of the column, and especially the tentacles, where they are packed in high densities. Each cnida is a capsule containing a long, invaginated hollow thread (see Figure 1). When stimulated by chemical or mechanical cues, the permeability of the cnida increases and water enters, increasing the pressure and blowing the thread inside out. Cnidae are usually released from the ectodermal cells when discharged. The largest cnidae (penetrants) contain the neurotoxins that are injected into prey via the hollow thread. Smaller cnidae include the volvents , which coil spontaneously on contact, and glutinants , which are adhesive.

Once a prey item is captured and paralyzed by the tentacles, body fluids leaking from puncture wounds stimulate a simple feeding response in the hydra. This involves a shortening of the tentacles, expansion and opening of the mouth, and the engulfing of the victim. The major stimulant for this response is the common tri-peptide (a chain of 3 amino acids), glutathione. Digestion of the prey item in the gastrovascular cavity proceeds over several hours. Large molecules are taken up by the gastrovascular cells, where digestion is completed. Cuticles and other undigested remains are subsequently expelled through the mouth. Almost any small invertebrates, up to the size of the hydra, may be consumed, including annelid worms, rotifers, insect larvae, and (especially) small crustaceans, such as Daphnia , Chydorus and Cyclops spp.

Hydra reproduce in the summer months. Most reproduction is asexual involving a process termed budding, in which a new hydra develops as a bud from the parent column (see species illustration). Buds later break free, but are genetically identical to the parents (clones). Under favorable conditions, hydra may possess several buds at various stages of development. Sexual reproduction is usually confined to late summer. Ovaries develop as oval swellings near the column base, while testes form as conical projections higher up. Hydra oligactis is dioecious , with males and females occurring as separate individuals. However, most species are hermaphrodites, the testes and ovaries developing on the same animal. Sperm swim out from the testis and enter the ovaries of other individuals. Ovaries each contain a single egg. Once fertilized, this egg develops a protective ornamented shell and frequently enters a stage of arrested development or dormancy. When favorable conditions return (often in the following spring), development resumes and the young hydra develops directly without a larval stage.

Answer 3

Hydroids are found in the shallow waters of the sea in the kelp, and they are attached to the seaweeds and the rocks.

Answer 4

Hydra live in fresh water environments, other cnidarians live in marine environments

Answer 5

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The hydra had it lair near the lake of Lerna in the Argolid.

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Answer 6

Hydras live in freshwater.