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- Cnidarians are a taxonomic group that includes Jellyfish, Polyps, and Corals.
- Many species have two forms: jellyfish and polyp. Each form is born in an alternation of generations. A jellyfish gives birth to polyps and polyps give birth to jellyfish.
- Corals are colonies of tiny polyps, all protected by a calcified skeleton. Normally the polyps remain inside their skeleton during the day and are only visible at night.
- Siphonophores such as Man-o-war and Vellela are colonies of specialized cnidarians, each type with a different function. Some help the creature hold on to rocks, some help it float. Some have weapons for hunting and defense, and some help in reproduction.
- Cnidarians’ bodies are as simple as a tennis ball turned inside itself, with a single hole in the center, as a mouth and an anus, surrounded by tentacles.
- In polyps the mouth looks upwards and in jellyfish it faces downwards.
- All cnidarians have special cells called nematoblasts in their tentacles. These are like microscopic harpoons, which detonate when something touches them. This is how these soft-bodied creatures defend themselves or hunt for food.
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| Sea Anemone; photo by Cliff1066tm cc-by |
Corals; photo by Jayhem cc-by |
Flag Jellyfish; photo by Evelyn Proimos cc-by |
Sources:
-Kayal, Ehsan; et al. (13 April 2018). "Phylogenomics provides a robust topology of the major cnidarian lineages and insights on the origins of key organismal traits". BMC Evolutionary Biology.
-The Variety of Life, Colin Tudge, 2000
Citation: García, A.I. 2015. The Tree Of Nature (Online) at http://thetreeofnature.com
