The parvorder of Odontocetes – the toothed whales – include sperm whales, beaked whales, killer whales, dolphins and porpoises. Generally the teeth are designed for catching fish, squid or other marine invertebrates, not for chewing them, so prey is swallowed whole. Teeth are shaped like cones (dolphins and sperm whales), spades (porpoises), pegs (belugas), tusks (narwhals) or variable (beaked whale males). Female beaked whales' teeth are hidden in the gums and are not visible, and most male beaked whales have only two short tusks. Narwhals have vestigial teeth other than their tusk, which is present on males and 15% of females and has millions of nerves to sense water temperature, pressure and salinity. A few toothed whales, such as some killer whales, feed on mammals, such as pinnipeds and other whales.