Whale (origin Old English hwæl) is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to the suborder Odontoceti (toothed whales). This suborder also includes the sperm whale, killer whale, pilot whale, and beluga whale. The other Cetacean suborder, Mysticeti (baleen whales), comprises filter feeders that eat small organisms caught by straining seawater through a comblike structure found in the mouth called baleen. This suborder includes the blue whale, the humpback whale, the bowhead whale and the minke whale. All cetaceans have forelimbs modified as fins, a tail with horizontal flukes, and nasal openings (blowholes) on top of the head.