Family: Trochidae. This family includes around 180 species found throughout the world. Tops vary in size and color, but all have a pyramidal shape. They are found in tidal rock pools as well as deep ocean depths and feed on seaweed and sponges. Top shells, like many mollusks, produce a flat, thin, circular trap door or operculum, which is often translucent or black. The trap door grows at the end of the muscular foot, providing protection for the mollusk as it withdraws inside the shell. Interesting Facts: Female top snails are larger than males. The animal is a popular source of food in some areas of the world. The commercial trochus shell (Trochus niloticus) is used to make pearlized buttons for clothing sold throughout the world and is one of the leading industries in the Philippine Islands.