This cell type is significant because it is similar to a type of protistan that forms colonies, the choanoflagellates , and suggests to us how multi-celled animals may have arisen from colonial protistans. Both choanocytes and choanoflagellates have a flagellum and a collar. The common name for poriferans, of course, is sponges. The other sponges lack calcium carbonate or mineral inclusions and are therefore softer. Some of these are the sponges we know as commercial sponges or bath sponges.
Sponges are diverse in color and shape and can be very beautiful.
They have nerve nets, a decentralized form of nervous system that permits coordinated behavior. A feature common to all cnidarians is the stinging nematocyst . These structures are found inside specialized cells called cnidocytes, and they often are associated with venom. A show of hands revealed that a surprising number of members of the class have been stung by jellyfish. Several remedies were offered, with the one most frequently mentioned being meat tenderizer.