well they have 1 and its open
This will depend upon the insect that you are talking about. Some have only two chambers and others can have a lot more.
Yes; many cnidarians have an exoskeleton.
Cnidarians do not have legs. Many have stinging tentacles. The number of these varies by species.
Cnidarians do no possess eyes for sight, though many of them are able to sense light vs dark.
1
200
small cnidarians and big cnidarians
Cnidarians include jellyfish and corals. Cnidarians are less complex than annelids or mollusks because the latter have gills with many layers of tissue.
5 chambers
cnidarians have no nervous system
The cnidarians are in the Kindom family
Yes, cnidarians are invertebrates.