1922C.E., William Marion Goldsmith, The Laws of Life, Richard G. Badger; Chapter VIII, page #162:
Technically, the terms cœlom and body cavity are not always synonymous ; but, this should not be confusing. The cœlom is found either in the embryo or adult stage in all forms of life from the earthworm to man, inclusive. Most zoölogists consider the cœlom of sufficient importance to be the basis upon which to divide all metazoa into two classes : acœlomata (without) and cœlomata (with a cœlom). It is, as yet, uncertain whether or not the Platyhelminthes (flatworms) and the Nemathelminthes (roundworms) possess a cœlom. This places them as connecting links between the acœlomata and cœlomata.
