The correct option is siphon.
Siphons are the part of mantle. These are hollow tube-like structures present in the aquatic mollusks. The cilia on their gills draw in sea water through siphons. The water moves down one siphon tube, over the gills, and out the other siphon tube. The water flow is used for one or more purposes such as locomotion, feeding, respiration, and reproduction
