The prosome of pterobranchs is specialized into a muscular and ciliated cephalic shield used in locomotion and in secreting the coenecium. The mesosome extends into one pair (in the genus "Rhabdopleura") or several pairs (in the genus "Cephalodiscus") of tentaculated arms used in filter feeding. The metasome, or trunk, contains a looped digestive tract, gonads, and extends into a contractile stalk that connects individuals to the other members of the colony, produced by asexual budding. In the genus "Cephalodiscus", asexually produced individuals stay attached to the contractile stalk of the parent individual until completing their development. In the genus "Rhabdopleura", zooids are permanently connected to the rest of the colony via a common stolon system.