Latin name: Cnidaria
Average lifespan: about 3 years
Size: Cnidarians range in size from nearly microscopic to more than 100 ft (30 m) long
Weight: and more than a ton (910 kg) in weight.
Group name: Colonies
Cnidaria are some of the simplest and most beautiful "animals." These creatures are flower-like and resemble plants in many respects. However, they have a mouth and a simple digestive system at the center of their tentacles. Because of these two features, these creatures are considered animals and not plants. There are 9000 species of Cnidaria.
What does a Cnidaria look like?
Most cnidarians have tentacles with stinging cells surrounding their mouth. The mouth is the only body opening. All cnidarians have radial symmetry. Cnidarians are said to be the simplest organisms at the tissue grade of organization. Their cells are organized into true tissues. Cnidarians are essentially bags made of two cell layers. The outer layer, or epidermis, contains the cnidocysts, the stinging cells that are characteristic of the phylum. The inner layer, or gastrodermis, lines the gut. In between epidermis and gastrodermis is the mesoglea, a layer of jelly-like substance, which contains scattered cells and collagen fibers. The mouth is often, but not always, surrounded by a ring of tentacles.
Where does the Cnidarian live?
All Cnidarians live under water; most live in the oceans and seas, and a few live in freshwater. But they mostly live in saltwater or oceans.
What does a Cnidarian eat?
Many eat small creatures or trap detritus, plankton and other microscopic titbits. But many also capture and eat large prey. Many cnidarians, however, more supplement their meals with food provided by photosynthetic zooxanthellae (symbiotic single-celled algae) that they harbour in their tentacles and bodies. These algae produce food from sunlight.
Did you know about these Cnidaria facts?
The two different forms of a Cnidarian body
A Cnidarian can have one of two basic body types, polypoid or medusoid.
The polypoid is the configuration of corals and anemones, with the tentacles and mouth generally facing up, and the other side affixed to a substrate or connected to a colony of other creatures of the same species.
In the Medusoid form, the organism is essentially upside-down, with the mouth and tentacles generally pointed down. These types of Cnidarians are usually free-swimmers, like jellyfish.
Most Cnidarians alternate between these two stages, although some, sea anemones and corals for example, do not have an alternation of generations.
Download free Cnidarian wallpapers, click on the image to open the large version.
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Cnidarian coloring pages
Download free Cnidarian coloring pages, click on the image to open the large version.