The correct option is C Amphiblastula
Amphiblastula is the larva of Scypha. It is formed by inversion of stomoblastula and they undergo gastrulation by invagination. It is a free swimming larva. Amphiblastula is partly flagellated and partly non-flagellated. It is the characteristic larva of the Calcarea and of some members of the Demospongiae. Thus, the correct answer is option C.