The Collaborative International Dictionary of English v.0.48:

Epicoele \Ep"i*coele\ ([e^]p"[i^]*s[=e]l), n. [Pref. epi- + Gr.
   koi^lon a hollow.] (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.
   [1913 Webster]