Information: - In animal anatomy, the notochord is a flexible rod made out of a material similar to cartilage. If a species has a notochord, it is, by definition, a chordate. The notochord lies along the anteroposterior ("head to tail") axis, is usually closer to the dorsal than the ventral surface of the animal, and is composed of cells derived from the mesoderm. The notochord has been observed to have many functions including developmental functions. The most commonly cited functions are as a site of muscle attachment, vertebral precursor, and as a midline tissue that provides signals to the surrounding tissue during development. - In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum. - A fish is any member of a group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification. - The beak, bill, or rostrum is an external anatomical structure of birds that is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young. The terms "beak" and "rostrum" are also used to refer to a similar mouth part in some dicynodonts, Ornithischians, cephalopods, cetaceans, billfishes, pufferfishes, turtles, Anuran tadpoles and sirens. - Snail is a common name that is applied most often to land snails, terrestrial pulmonate gastropod molluscs. However, the common name "snail" is also applied to most of the members of the molluscan class Gastropoda that have a coiled shell that is large enough for the animal to retract completely into. When the word "snail" is used in this most general sense, it includes not just land snails but also thousands of species of sea snails and freshwater snails. Occasionally a few other molluscs that are not actually gastropods, such as the Monoplacophora, which superficially resemble small limpets, may also informally be referred to as "snails". - Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a "backbone" or "spine"), derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include insects; crabs, lobsters and their kin; snails, clams, octopuses and their kin; starfish, sea-urchins and their kin; and worms. - Clam is the general common name of any mollusks within the class Bivalvia. More specifically, true clams are bivalves having two shells of equal size connected by two adductor muscles and having a powerful burrowing foot. They are infaunal, spending most of their lives partially buried in the sand of the ocean floor. These characteristics distinguish the true clams from other bivalves, such as oysters, mussels, and scallops. - 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. - Birds (Aves), also known as avian dinosaurs, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Birds live worldwide and range in size from the bee hummingbird to the ostrich. They rank as the class of tetrapods with the most living species, at approximately ten thousand, with more than half of these being passerines, sometimes known as perching birds or, less accurately, as songbirds. - A claw is a curved , pointed appendage , found at the end of a toe or finger in most amniotes ( mammals , reptiles , birds ) . However , the word '' claw '' is also often used in reference to an invertebrate . Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders , at the end of the leg or tarsus for gripping a surface as the creature walks . Crabs ' , lobsters ' and scorpions ' pincers , or more formally , their '' chelae '' , are sometimes called claws . A true claw , ( as opposed to a chela ) is made of hard protein called keratin . Claws are used to catch and hold prey in carnivorous mammals such as cats and dogs , but may also be used for such purposes as digging , climbing trees , self - defense , and grooming , in those and other species . Similar appendages that are flat and do not come to a sharp point are called nails instead . Claw - like projections that do not form at the end of digits , but spring from other parts of the foot are properly named spurs . Claws of animals like tigers , lions , and bears were used in making items such as ornaments , pendants , and brooches . - Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (= short, = tail), usually entirely hidden under the thorax. They live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and have a single pair of claws. Many other animals with similar names such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice are not true crabs. - In biology, a phylum (plural: phyla) is a taxonomic rank below kingdom and above class. Traditionally, in botany the term division was used instead of "phylum", although from 1993 the International Code of Nomenclature for algae, fungi, and plants accepted the designation "phylum". Depending on definitions, the kingdom Animalia contains approximately 35 phyla, Plantae contains about 12, and Fungi contains around 7. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta. - Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or "basket stars". About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, below the surface. - Worms are many different distantly related animals that typically have a long cylindrical tube-like body and no limbs. Worms vary in size from microscopic to over in length for marine polychaete worms (bristle worms), for the African giant earthworm, "Microchaetus", and for the marine nemertean worm (bootlace worm), "Lineus longissimus". Various types of worm occupy a small variety of parasitic niches, living inside the bodies of other animals. Free-living worm species do not live on land, but instead live in marine or freshwater environments, or underground by burrowing. - Insects (from Latin ', a calque of Greek ['], "cut into sections") are a class of invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae. They are the most diverse group of animals on the planet, including more than a million described species and representing more than half of all known living organisms. The number of extant species is estimated at between six and ten million, and potentially represent over 90% of the differing animal life forms on Earth. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, a habitat dominated by another arthropod group, crustaceans. Given the paragraphs above, decide what entity has the relation 'instance of' with 'anatomical structure'.
The answer to this question is:
claw