These blade-like teeth occlude (close) with a scissor-like action for shearing and shredding meat. Carnassials are most highly developed in the Felidae and the least developed in the Ursidae. Carnivorans have six incisors and two conical canines in each jaw. The only two exceptions to this are the sea otter (Enhydra lutris), which has four incisors in the lower jaw, and the sloth bear (Melursus ursinus), which has four incisors in the upper jaw. The number of molars and premolars is variable between carnivoran species, but all teeth are deeply rooted and are diphyodont. Incisors are retained by carnivorans and the third incisor is commonly large and sharp (canine-like). Carnivorans have either four or five digits on each foot, with the first digit on the forepaws, also known as the dew claw, being vestigial in most species and absent in some.