Pseudocoelomate

Part of speech: noun, adjective

Definitions

1. An animal having a fluid-filled body cavity between the gut and outer body wall that lacks a complete mesodermal lining
2. A creature with a pseudocoelom, a body chamber that is not fully enclosed by mesoderm tissue as in more complex animals
3. An organism possessing a body cavity that is incompletely lined by mesoderm, found in roundworms and certain other invertebrates

Etymology: "Pseudocoelomate" is a technical coinage built from two Greek-derived parts, not a word with an older life in English. Its first element comes from "pseudo-", Greek for "false," and the second from "coelom," the body cavity that lies between the gut and the outer wall of an animal, itself from Greek "koilōma," meaning "cavity" or "hollow." The "-ate" ending, used in biology to form adjectives describing an organism that has or possesses a feature, was attached to "pseudocoelom" to describe animals with this kind of body cavity. The term names animals such as roundworms, rotifers and horsehair worms, whose body cavity is only partly lined by the mesoderm, the middle germ layer that forms the lining of a true coelom in other animals. Their cavity is therefore a "false" coelom in the sense that it is not fully enclosed by the layer that lines it elsewhere. The noun form, used to refer to such an animal itself, was built from the adjective in the same way.