Please answer the following question: Information:  - The gray whale ("Eschrichtius robustus"), also known as the grey whale, gray back whale, Pacific gray whale, or California gray whale is a baleen whale that migrates between feeding and breeding grounds yearly. It reaches a length of , a weight of , and lives between 55 and 70 years. The common name of the whale comes from the gray patches and white mottling on its dark skin. Gray whales were once called devil fish because of their fighting behavior when hunted. The gray whale is the sole living species in the genus Eschrichtius, which in turn is the sole living genus in the family Eschrichtiidae. This mammal descended from filter-feeding whales that appeared at the beginning of the Oligocene, over 30 million years ago.  - A bristle is a stiff hair or feather (natural or artificial), either on an animal, such as a pig, or on a tool such as a brush or broom.  - Keratin is one of a family of fibrous structural proteins. Keratin is the protein that protects epithelial cells from damage or stress. It is the key structural material making up the outer layer of human skin. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals. The only other biological matter known to approximate the toughness of keratinized tissue is chitin.  - The blue whale ("Balaenoptera musculus") is a marine mammal belonging to the baleen whales (Mysticeti). At up to in length and with a maximum recorded weight of and probably reaching over 181 tonnes (200 short tons), it is the largest animal known to have ever existed.  - Animals are multicellular, eukaryotic organisms of the kingdom Animalia (also called Metazoa). The animal kingdom emerged as a basal clade within Apoikozoa as a sister of the choanoflagellates. Sponges are the most basal clade of animals. Animals are motile, meaning they can move spontaneously and independently at some point in their lives. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs: they must ingest other organisms or their products for sustenance.  - Rorquals / rrkwl / ( Balaenopteridae ) are the largest group of baleen whales , a family with nine extant species in two genera . They include what is believed to be the largest animal that has ever lived , the blue whale , which can reach 180 tonnes ( 200 short tons ) , and the fin whale , which reaches 120 tonnes ( 130 short tons ) ; even the smallest of the group , the northern minke whale , reaches 9 tonnes ( 9.9 short tons ) . Rorquals take their name from French rorqual , which derives from the Norwegian word røyrkval , meaning `` furrow whale '' .  - Baleen whales (systematic name Mysticeti), known earlier as whalebone whales, form a parvorder of the infraorder Cetacea (whales, dolphins and porpoises). They are a widely distributed and diverse parvorder of carnivorous marine mammals. Mysticeti comprise the families Balaenidae (right whales), Balaenopteridae (rorquals), Cetotheriidae (the pygmy right whale), and Eschrichtiidae (the gray whale). There are currently 15 species of baleen whale. While cetaceans were historically thought to have descended from mesonychids, molecular evidence supports them as relatives of even-toed ungulates (Artiodactyla). Baleen whales split from toothed whales (Odontoceti) around 34 million years ago.  - Mammals are any vertebrates within the class Mammalia (from Latin "mamma" "breast"), a clade of endothermic amniotes distinguished from reptiles and birds by the possession of a neocortex (a region of the brain), hair, three middle ear bones and mammary glands. The sister group of mammals may be the extinct "Haldanodon." The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade. The mammals consist of the Yinotheria including monotrema and the Theriiformes including the theria.  - The bowhead whale ("Balaena mysticetus") is a species of the family Balaenidae, in suborder Mysticeti, and genus "Balaena", once thought to include the right whale.  - The fin whale ("Balaenoptera physalus"), also called the finback whale, razorback, or common rorqual, is a marine mammal belonging to the suborder of baleen whales. It is the second-largest animal after the blue whale. The largest reportedly grow to long with a maximum confirmed length of 25.9 m (85 ft), a maximum recorded weight of nearly , and a maximum estimated weight of around . American naturalist Roy Chapman Andrews called the fin whale "the greyhound of the sea... for its beautiful, slender body is built like a racing yacht and the animal can surpass the speed of the fastest ocean steamship."  - Baleen is a filter-feeder system inside the mouths of baleen whales. The baleen system works by whale opening its mouth underwater and taking in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as food source for the whale. Baleen is similar to bristles and is made of keratin, the same substance found in human fingernails and hair. Baleen is a skin derivative. Some whales, such as the bowhead whale, have longer baleen than others. Other whales, such as the gray whale, only use one side of their baleen. These baleen bristles are arranged in plates across the upper jaw of the whale. Baleen is often called whalebone, but that name also can refer to the normal bones of whales, which have often been used as a material, especially as a cheaper substitute for ivory in carving.  - Roy Chapman Andrews (January 26, 1884  March 11, 1960) was an American explorer, adventurer and naturalist who became the director of the American Museum of Natural History. He is primarily known for leading a series of expeditions through the fragmented China of the early 20th century into the Gobi Desert and Mongolia. The expeditions made important discoveries and brought the first-known fossil dinosaur eggs to the museum. His popular writings about his adventures made him famous.    After reading the paragraphs above, choose the best answer for the entity that related to 'rorqual' with the relationship of 'parent taxon'.  Choices: - animal  - artiodactyla  - balaena  - blue whale  - california  - dinosaur  - eschrichtius  - fin whale  - human  - mammal  - metazoa  - musculus  - mysticeti  - pig  - rorqual  - sauropsida  - theria  - theriiformes
A:
mysticeti