Epicoele

Ep´i`coele

    (ĕp´ĭ`sēl)
n.1.(Anat.) A cavity formed by the invagination of the outer wall of the body, as the atrium of an amphioxus and possibly the body cavity of vertebrates.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.