protocoelomate
/ˌprəʊtə(ʊ)ˈsiːlə(ʊ)meɪt/Zoology rare
noun
Originally: (A. S. Hyatt's name for) a member of a grade of primitive multicellular animals characterized by a simple central cavity with branching sacs (not now considered coelomic), comprising most or all of the sponges. Now: a metazoan animal considered to represent or resemble a common ancestor of coelomate phyla.
Origin
Late 19th century. From proto- + coelomate. Compare scientific Latin protocoelomata.