The highest category or level in the Linnaean system of classification.

The category or level in the Linnaean classification system in which organisms are primarily distinguished on the basis of overall basic body plan or organization (e.g., soft, unsegmented bodies in contrast to external skeletons along with jointed bodies and limbs).

The category or level in the Linnaean system of classification in which organisms are primarily distinguished on the basis of cellular organization and methods of nutrition. Whether they are single- or multiple-celled and whether they absorb, ingest, or produce food are also critical factors.

The kingdom that includes organisms that do not produce their own food but must eat other organisms to obtain it. They have nerves and muscles that aid in controlled movement around their environment.

The kingdom that includes organisms that produce new cell matter out of inorganic material by photosynthesis. They do not have the ability to move around their environment except by growing or being transported by wind, water, or other external forces.

The characteristic of left and right sides of the body generally being mirror images of each other. If there are two functionally similar body parts, they are usually found roughly equidistant from the center line, parallel to each other.

A rudimentary internal skeleton made of stiff cartilage that runs lengthwise under the dorsal surface of the body of some animals. Generally, there is a single hollow nerve chord on top of it. Among humans and the other vertebrates, this structure is replaced by a more complex skeleton following the embryonic stage of development.

The phylum of animals that have elongated bilaterally symmetrical bodies. In some phase of their life cycle, they have a notochord and gill slits or pouches. Members of this phylum also often have a head, a tail, and a digestive system with an opening at both ends of the body. This phylum includes fish, amphibians, reptiles, birds, mammals, and 2 invertebrate subphyla (tunicates and lancelets). Humans are members of this phylum.

The phylum of animals that is characterized by external skeletons as well as jointed bodies and limbs. Insects, spiders, centipedes, lobsters, and crabs are members of this phylum.

The phylum of animals that is characterized by soft, unsegmented bodies that are usually, but not always, enclosed in hard shells. They also usually have at least one strong foot that helps them move. Octopi, squids, snails, slugs, clams, and other shellfish are members of this phylum.

Organs in some animals that are used to obtain oxygen under water. In the case of humans, other mammals, birds, and reptiles, lungs replace rudimentary forms of these organs after the embryonic stage of development. Frogs replace them with lungs in the transition from tadpoles to adults. Fish retain them all of their lives.

The subphylum of chordates in which the notochord is replaced by a more complex spinal chord late in the embryonic stage of development. The spinal chord is protected by a segmented vertebral column of cartilage and/or bone.

The level of classification immediately below phylum and above class in the Linnaean classification system.