The name comes from Ancient Greek κοῖλος (koîlos) 'hollow' and ἔντερον (énteron) 'intestine', referring to the hollow body cavity common to these two phyla.

The body has a single opening, the hypostome, surrounded by sensory tentacles equipped with either nematocysts or colloblasts to capture mostly planktonic prey.

The scientific validity of the term coelenterate is currently rejected, as the Cnidaria and Ctenophora have less in common than previously assumed.

[4] In particular, the phylogenetic position of Ctenophora is controversial; it was first considered a sub-group of coelenterata but Hyman regarded it as a separate phylum.

Complicating the issue is the 1997 work of Lynn Margulis (revising an earlier model by Thomas Cavalier-Smith) that placed the Cnidaria and Ctenophora alone in the branch Radiata within Eumetazoa.