The correct option is A Sycon
Amphiblastula is the larva of Scypha or Sycon. 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 Sycon.
Thus, the correct answer is option A.