rhagon

from The Century Dictionary.

• noun A type of sponge-structure resulting from the modification of a primitive form, as an olynthus, by the outgrowth of the endoderm into a number of approximately spherical chambers communicating with the exterior by a prosopyle and with the paragastric cavity by an apopyle (see prosopyle), with conversion of the flagellated into pavement epithelium except in the chambers.