Gill-slits do not open directly to outside.Each gill-slits opens into a gill pouch called branchial sac, which lies between the bodywall and the pharynx.Each branchial sac in turn opens to the exterior by a small independent gill pore.In B.misakiensis the first four pouches become united .The collar coelom also communicates with the common branchial sac of its side through a collar canal.The gill -pores are visible externally in two longitudinal rows one on each side of the mid-dorsal ridge in the branchiogenital region of the trunk.
No comments:
Post a Comment