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Can you tell the difference between the corals and the plants? Look closely!
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Cnidarians

The Cnidaria phylum consists of animals with stinging cells called cnidoblasts. This includes corals, jellyfish, anemones and hydroids. Cnidarians do not have a head, and commonly look like a flower. The petals are actually tentacles which contain the cnidoblasts. There are over 9000 species living today.

Corals are often mistaken by amateurs to be plants. For example, the coral in the image are on the left, the right side is full of plants! In reality, there are both soft and hard corals, but all of them are animals. Hard corals form coral reefs, which serve as the base for important ecosystems. Without them, many marine animals would become extinct. Hard corals have two parts: a hard outer shell called a corallite, and soft tissues called polyps. Corals are so pretty that some people make reef aquariums.

Jellyfish are different from corals in that they can move around in the water. The typical jellyfish has a round, bowl-shaped top with tentacles handing down. Although they are very pretty, jellyfish should be avoided because their stings can be very dangerous. They come in a range of sizes, from a few inches to 3 feet. Flecker's Box-jelly is the largest jellyfish and also the most dangerous. It is responsible for hundreds of deaths.

Last modified February 24, 2011 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA