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Diet -- carnivore, especially cattle and humans. Another of the fierce offspring of Echidna and Typhon, the Hydra was a large serpent with multiple heads and poisonous breath. A nephew helped him by cauterizing each wound as a head was lopped off. The last head was immortal, so Heracles buried it under a large rock. The Hydra possesses a regeneration ability to not only regrow its head but also grow more heads in a similar albeit less impressive way to how some lizards can regrow their tail.
Its long neck may be used for reaching into treetops, water, or caves for prey. Age of Empires Series Wiki Explore. The Titans Tale of the Dragon. Explore Wikis Community Central. Edit source History Talk 0.
Do you like this video? Play Sound. Pre-released screenshot featuring a Hydra on the right. Upon contact with prey, the contents of the stinging cells are explosively discharged, firing stings that can paralyze small animals. Biologists are especially interested in hydra because of their remarkable regenerative ability — they do not appear to die of old age, or to age at all. In this article, you will learn about this fantastic creature in detail: by definition, classification, and cellular structure.
I will show you several interesting behaviors when a hydra feeds or move. We will also see what happens to a sick hydra. Finally, you will also learn where and how to collect a hydra for your microscopic project.
Hydras are classified under the phylum Cnidaria and the class Hydrozoa. Examples of Cnidarians include jellyfish , sea anemones , corals , and hydras. They are predominantly marine species, but a smaller number of species including hydras are found in rivers and freshwater lakes. Cnidarians are incredibly diverse. Examples of Cnidarians include jellyfishes, sea anemones, corals, and hydras. Photo credit: Dr.
Sebastian Fraune. Hydras live in all kinds of freshwater habitats, including ponds, ditches, and slow-flowing rivers and streams. They are native to temperate and tropical regions. Hydra usually anchors itself to a substrate like a water plant by its foot. Photo credit: Jan Hamrsky. Yes, hydra has a low tolerance for pollution. Since hydra cannot be found in contaminated water, they can be used as a biological indicator to rank toxicants on the level of a potential hazard.
Their tentacles may extend much longer — some species of green hydra may measure about 5 cm to 20 cm when extended. The body of a hydra may retract while sensing a danger , making the organism appear shorter and rounded. Stentors are almost the largest single-celled ciliates and can grow up to 4 mm.
You can see the hydra is much bigger than stentors. A small hydra may look transparent in its tentacles and yellowish in its tube-like body. Hydra oligactis is brown; therefore, also known as the brown hydra Hydra viridissima is commonly called green hydra because of its distinctive color due to the symbiotic green algae Chlorella that live within its body. Right: Hydra viridissima. Photo credit: Hydra oligactis , Hydra viridissima. Hydra has a tubular body with radial symmetry.
The radial symmetry is also a shared feature of the phylum Cnidaria. You can see the body wall of a Hydra consisting of two layers of cells. Hydra has two main body layers. The outer layer is the epidermis like our skin which can secret a protective layer hydramacin against bacterial infection. Respiration and excretion occur by diffusion through the surface of the epidermis.
The inner layer is called the gastrodermis , which lines the stomach. Between the two layers is a gel-like substance called mesoglea. Modified from Vogg MC. The bottom end of a hydra is secured on the surface by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that accounts for its adhesive properties.
At the free end of the body is a mouth opening hypostome surrounded by tentacles. The mouth is connected to the body cavity. The prey captured by the tentacles will then be engulfed within the body cavity for digestion. Since hydra has only one opening, the waste after digestion will be discharged through the same mouth opening. Tentacles from 6 to 10 in number radiate outward from the rim of the mouth. These tentacles can be greatly extended at the time of feeding or locomotion.
Each tentacle is covered with highly specialized stinging cells called cnidocytes. Cnidocytes contain specialized structures called nematocysts , which look like miniature light bulbs with a coiled thread inside. Near the outer edge of the cnidocyte is a short hair, called a cnidocil. The cnidocil functions like a trigger to control the firing of a nematocyst. Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release.
These toxins can paralyze the prey. A cnidocyte fires a structure that contains the toxin from a characteristic subcellular organelle called a nematocyst. Left: a cnidocyte at the resting stage. Right: a fired cnidocyte. Hydra does not have a recognizable brain or true muscles, but hydra has a primitive nervous system called the nerve net. Nerve nets connect sensory photoreceptors light-sensitive and touch-sensitive nerve cells located in the body wall and tentacles. This simple nervous system helps hydra quickly respond to all kinds of stimuli.
You can see the hydra has a network-like nerve system. Photo credit: ck Photo credit: U Heidelberg. Hydras mainly feed on aquatic invertebrates such as Daphnia. While feeding, Hydras extend their body to maximum length and then slowly extend their tentacles. Once fully extended can be four to five times the length of the body , the tentacles are slowly maneuvered around, waiting for contact with suitable prey. Upon contact with prey, hundreds of nematocysts can fire their stings and neurotoxins at the same time.
This can paralyze the prey. Within minutes, the tentacles can surround the prey and move the prey into the opened mouth aperture. The prey will then be engulfed within the body cavity for digestion. Hydra can stretch its body wall considerably in order to digest prey more than twice its size. Since hydra has no anal pore, the indigestible remains of the prey will be discharged through the mouth aperture via contractions.
The mouth disappears after it eats, meaning a hydra regrow a new mouth for each bite. Is that amazing? Some Hydra species like Hydra viridissima can form a symbiotic relationship with green algae Chlorella living within its body. Hydra provides a safe place to live, and green algae synthesize food by photosynthesis in return.
This symbiosis gives a significant advantage to hydras when environmental conditions change food is scarce. In the absence of prey, a green hydra may still be able to survive for about 3 months using nutrients produced through photosynthesis.
This allows the hydra to tolerate starvation. Green hydra Hydra viridissima and its symbiotic algae Chlorella sp. Modified from Marinespecies. Typically, a hydra remains attached by the basal disc to some suitable object in the water.
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