What do sponge jellyfish crab have common in?

Sponges, jellyfish, and crabs are all members of the phylum Cnidaria, which is a group of aquatic invertebrates. Cnidarians are characterized by their radial symmetry, a body plan that is made up of a central axis surrounded by a ring of tentacles. They also have a gastrovascular cavity, which is a digestive system that is used to both ingest and expel food.

Sponges are the simplest type of Cnidarians and they lack tissues and organs. Jellyfish are more complex Cnidarians and they have a body that is made up of a gelatinous substance called mesoglea. Crabs are the most complex type of Cnidarians and they have a body that is made up of a hard exoskeleton.