have a comparatively simple physiology. They are basically a sac
of jelly which contains their internal organs. The sac has an opening
their mouth, this is surrounded by tentacles. The tentacles have
stinging structures called nematocysts, which are used to stun or
paralyse their prey. After stinging, the tentacles pull the
prey into the mouth. Each individual is known as a polyp. Coelenterates
that are found on Cornish shores include the sea anemones, true
jellyfish and the hydroids.