Coel--- is from the Latin Coelus, heaven. In late Latin, pronounced, as you correctly noted, chaylus, as in Regina Coeli (re-geena chaylee). In the English pronunciation which used to be used, this comes out as regina (rhymes with vagina) see-lye. So the prefix 'coel' would be pronounced seel and coelocanth is see-lo-canth. (I think this is the correct spelling.)