| A | B |
|---|
| amniote egg | Egg that has extraembryonic membranes and often a shell. Contributed to successful invasion of land by vertebrates. |
| bird | Vertebrate with reptilian ancestry; only organism that produces feathers. |
| cartilaginous fish | Jawed fish with a cartilage endoskeleton and prominent fins (the sharks). |
| chordate | Animal having a notochord; dorsal hollow nerve cord; pharynx; and gill slits in pharynx wall during at least part of life cycle. |
| fin | In fish an appendage that helps stabilize propel and guide body in water. |
| fish | An aquatic animal of the most ancient diverse vertebrate lineage; |
| gill slit | Opening in a thin-walled pharynx. Gill slits serve in food trapping and respiration; jaws evolved from certain gill slit supports. |
| hominid | All species on or near evolutionary road leading to modern humans. |
| hominoid | Apes humans and recent ancestors. |
| jaw | In chordates either of two cartilaginous or bony parts bordering the mouth typically bearing teeth used to secure or pummel food. Many invertebrates have similar opposing parts. |
| lancelet | A filter-feeding invertebrate chordate with a body tapered at both ends. |
| lung | Internal sac-shaped respiratory surface that evolved in oxygen-poor habitats as an adaptation that increases the surface area for gas exchange. |
| mammal | Vertebrate whose females nourish offspring with milk from mammary glands. |
| notochord | In chordates a rod of stiffened tissue (not cartilage or bone) that is a supporting structure for the body. |
| ostracoderm | One of the earliest jawless fishes; a bottom-dwelling filter feeder. Extinct. |
| placenta | Blood-engorged organ of pregnant female placental mammals; made of endometrial tissue and extraembryonic membranes. Permits exchanges between the mother and fetus without intermingling their bloodstreams; sustains the new individual and allows its blood vessels to develop separately. |
| primate | Mammalian lineage dating from the Eocene; includes prosimians tarsioids and anthropoids |
| scale | In fish a small bony plates that protect the body surface without weighing it down. |
| swim bladder | Adjustable flotation device that helps many fishes maintain neutral buoyancy in water; its volume changes as it exchanges gases with blood. |
| vertebra | One of a series of hard bones that serve as a backbone and that protect the spinal cord. |
| vertebrate | Animal having a backbone. |
| amphibian | Vertebrate with a body plan and reproductive mode somewhere between fishes and reptiles and a mostly bony endoskeleton. |
| bipedalism | Habitually walking upright on two feet as by ostriches and hominids. |
| bony fish | Type of fish with an endoskeleton usually well developed |
| dentition | the type size and number of an animal's teeth. |
| filter feeder | Animal that filters food from a current of water directed through a body part |
| gill | Respiratory organ that have a thin moist vascularized layer for gas exchange. |
| hagfish | Type of scavenging jawless fish that secretes slimy mucus. |
| human | A primate of the species Homo sapiens. |
| lamprey | Type of predatory jawless fish that has a cylindrical body with a cartilaginous skeleton and an oral disk with rasping parts. |
| lobe-finned fish | Only bony fish with skeletal supporting elements inside a pair of thick ventral fins; also has paired lungs. Lineage probably included ancestors of amphibians. |
| nerve cord | A prominent longitudinal nerve; most animals have one; two or three. |
| pharynx | In land vertebrates this is a dual entrance to the esophagus and trachea. |
| placoderm | One of the earliest fishes with jaws and paired fins; extinct. |
| reptile | Carnivorous species belonging to the first vertebrate lineage to escape dependency on free water by way of internal fertilization with efficient kidneys and an amniote eggs. |
| tunicate | A baglike filter-feeding urochordate. |
