Coeloptychium
Coeloptychium is an extinct genus of lychniscosidan hexasterophoran sea sponge which has often been used as an index fossil. Its remains have been found in Cretaceous sediments in Germany, Belgium, France and the UK. Coeloptyhcium is best preserved in Campanian sediments in Germany. The type species, C. agaricoides, was named in 1826.