Sterroblastula

a stage of embryonic development in many invertebrates, for example, in some coelenterates, worms, and mollusks; a type of blástula. A sterroblastula usually forms as a result of the spiral cleavage of an egg. It looks like a compact sphere. Unlike other types of blástulas—coeloblastulas and discoblastulas—sterroblastulas have no cavity.