The body of a cnidarian may look very simple, but it can be very complex. Inside of a
cnidarian there is a gastrovascular cavity, which consists of a mouth and an anus, and is used for digestion. There
is a nerve net, with no brain, which is used to control movement, and is made of many simple receptors. Some cnidarians
can have complex nerve systems with eyes that include lenses and retinas. In order to sense where they are at and to
sense gravity, cnidarians have a structure called a statolith, which is located in the inner ear. Also, the one thing
that distiguishes cnidarians from any other phylum is the tentacles located around their mouth. These tentacles contain
nematocysts, which are stinging cells. These cells are used to capture food and defend themselves from other animals.