Cnidarians are essentially bag shaped organisms with a mouth but no anus, and they usually have tentacles around the mouth. Cnidarians are characterized by nematocysts. Cnidarians are conspicuous and common inhabitants of both the sea and open waters. Some species are holoplanktonic, but others have an asexual benthic stage in their life cycle and their medusae are part of the meroplankton.
The information came from the following websites.
www.cnidaria.org -This site is about
a Cnidarian Research Institute
www.ucmp.berkeley.edu/cnidaria/cnidaria.html-Cnidarians
For more information see