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| Lettuce coral |
There are about 9000 species of cnidarians that include the jellyfish (meduza), corals, sean anemones (tengeri rozsák) and hydra. The majority are tropical and sub-tropical and living in coastal waters. There are a few freshwater species. Some are sessile (don't move), while others are free-swimming. Some are solitary and others are colonial.
Body structure
- radial symmetry
- true tissues, but no organs
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| The body structure of cnidarians in polyp and medusa form. The gastrovascular cavity is where digestion occurs and gases are exchanges with the water. |
- special stinging cells on tentacles, called cnidocytes (csalánsejtek) that contain nematocysts (the stinging, thread-like part). Once the prey is stung, it is paralyzed and can be pulled/pushed into the animal's mouth using its tentacles
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| Cnidocyte and how it works |
- simple diffused nerve net for their nervous system (hálozatos idegrendszer), controls complex body activities like swimming, sliding and even somersaulting (as well as hunting, of course)!
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| Cnidarian nerve net |
Reproduction
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| Reproduction in jellyfish |
Some species of cnidarians don't go through a full life cycle, they only exist in one form (eg. they are only polyps). In these cases, we can observed a slightly reduced life cycle, where asexual or sexual reproduction actually occurs in either form.
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| A generalized life cycle |
Classification
1. Hydrozoa (hidraállatok): are only in the polyp form, includes some freshwater species
2. Scyphozoa (kehelyállatok): are found in both polyp and medusa form, but the medusa form is the dominant form in their life cycle. These are the jellyfish
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| Moon jelly |
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| Taxateca jelly |
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| White spotted jelly |
3. Anthozoa (virágállatok): only have the polyp form. These are the corals and sea anemones
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| Sea anemone |
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| Sea anemone |
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| Brain coral |
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