Feeding mechanisms in the gastropod Crepidula fecunda

The gastropod Crepidula fecunda feeds in 2 distinct ways: grazing of the substrate and suspension feeding. The taenioglossan radula plays a role in both processes. In the former, the radula rasps the surface, and the material is immediately ingested. This means of food acquisition is mainly used by motile individuals, i.e. juveniles and adult males. Adult females are sessile, and are only able to rasp the area beneath the head region, severely limiting the amount of food acquired. Females brooding egg capsules are even more restricted, since the area normally grazed is occupied by the capsule mass. The second mode of feeding, suspension feeding, is exhibited by late juveniles and all adults. Suspended particles are captured in mucous nets on the ventral and dorsal surfaces of the single gill lamella. The entrained particles, loosely bound in mucus, are transported by ciliary action to the distal tips of the filaments, which are bulbous. The material accumulates in 2 mucous strings which traverse the ventral surfaces of the filaments at right angles to the filaments along the entire length of the distal margin of the gill. These strings coalesce into a single, thicker string, which is transferred at intervals to a food canal in the neck, where it is twisted into a compact, mucous cord by a spiral action of the neck canal musculature, The cord is moved through the neck canal to the buccal region, where it is grasped by the radula and ingested. Some material from the gill does not enter the neck canal but is carried by ciliary tracts to a modified region in the mantle, the food pouch, where it is compacted into a mucous ball, which is picked up by the radula and either ingested or rejected as pseudofaeces, In the case of rejection, the ball is pushed to the shell margin by the radula and lips. In C. fecunda food material is stored on the gill, allowing the radula time to undertake other tasks such as rasping the substrate and handling the mucous ball in the food pouch. This dual feeding mechanism diversifies the food and probably increases its nutritional value.