 The valves widen slightly at the front end, forming a narrow opening (or gape), through which water is pumped in at the sides and out from the middle.The ventral valve is slightly longer and slightly more convex.The margin of the valves is fringed by chitinous tan colored bristle (or chaetae), short at the side of the valves, but much longer at the front where they assist in keeping open the access of the body cavity to the outside water.