This type of trickle valve utilizes a specially designed duckbill rubber sleeve. Duckbill sleeve trickle valves have no moving parts. The duckbill valve is similar in function to the mitral valve in the heart. When pressure is removed, however, the duckbill end returns to its flattened shape, preventing backflow. Duckbill flash suppressors have upper and lower "prongs" and direct gases to the sides. Venefica is a genus of eels in the duckbill eel family Nettastomatidae. "Kritosaurus" was a hadrosaurine hadrosaurid, a flat-headed or solid-crested duckbill. Hemerocoetes is a genus of duckbill fishes. Duckbill eels are found along the continental slopes of tropical and temperate oceans worldwide. "Naashoibitosaurus" is a saurolophine hadrosaurid, a "flat-headed or solid-crested duckbill". The other end, the duckbill, retains its natural flattened shape. In the Neighborhood of Make-Believe, Henrietta has sewn curtains with a duckbill pattern. Nettenchelys bellottii is a species of duckbill eel in the family Nettastomatidae. Nettenchelys exoria is an eel in the family Nettastomatidae (duckbill/witch eels). Nettenchelys taylori is an eel in the family Nettastomatidae (duckbill/witch eels).