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This zoology glossary contains a wide variety of terms and definitions. Its aim is to help you to understand the vast language that has developed for the study of animals. Terms in this category begin with the letter 'A'.

Zoology Glossary Index:
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Abdomen
The hind portion of an animal's body, located below the rib cage in mammals and below the thorax in arthropods. In mammals, the abdomen contains the viscera excluding the heart and lungs.

Abscission
The process by which a part of an organism is shed or separates from the rest of the organism. Usually used in reference to plants, for example when fruit drops from the plant or when leaves are shed from a tree.

ACAP (Agreement on the Conservation of Albatrosses and Petrels)
The Agreement on the Conservation of Albatrosses and Petrels (ACAP) binds signing countries to putting forth immediate efforts to reduce albatross deaths due to fishing lines.

Accidental
Pertaining to species that do not occur in a region under normal circumstances.

Acclimation
Reversible physiological or morphological changes an organism experiences in response to changing environmental conditions; such physiological changes enable the organism to tolerate the new environmental conditions.

Active Transport
The movement of ions or other substances across a membrane such in the direction of increasing concentration (and thus requires an expenditure of energy).

Activity Space
The range or spectrum of environmental conditions and characteristics suitable for the normal activity of an organism.

Adaptation
A genetically controlled characteristic of an organism that enhances its fitness by helping the organism to survive and reproduce. Through adaptation, organisms may become better suited and more successful in their environments over time.

Adaptive Function
A mathematical expression that takes into account the fitnesses of a phenotype in each of several different environments to produce a measurement of the general fitness of the phenotype in a varied environment.

Adaptive Radiation
A type of evolutionary change in which a number of new forms develop from a single original form in response to the availability of new habitats.

Aerial Behavior
A type of behavior exhibited by dolphins and whales in which the animal comes out above the surface of the water (for example, leaps, jumps, or bow rides). Such actions are thought to be forms of communicative or playful behavior.

After-shaft
A double feather that grows from the shaft of a body feather. An after-shaft is important in maintaining warmth and is known to occur in grouse, quail, and relatives.

Age Class
The set of individuals in a population that are all of a particular age or fall within a specfied age group.

Agonistic
Pertaining to behavior that opposes other that of other individuals and causes conflicts.

Aigrette
Breeding feathers characteristic of herons and egrets that are used in courtship displays. Aigrette feathers are long and loose.

Air Sac
A structure unique to the respiratory system of birds. Air sacs are thin-walled structures and through which air flows as the bird breathes.

Airfoil
A structure that creates lift as a result of the differential airflow over that occurs over its top and bottom surfaces. An example of an airfoil in the animal world is a bird's wing.

Allele
One of multiple alternate gene forms that are possible at a chromosomal location.

Alligator
A crocodilian that occurs in subtropical regions and can be distinguished from a crocodile in that it has a broader snout.

Allopatric
Pertaining to organisms that have different ranges due to geographical separation.

Alpha Diversity
A measurement of the variety of organisms that inhabit a defined region or habitat.

Altruism
A type of behavior in which an individual acts to further the welfare of other individuals.

Alula
A set of feathers on the leading edge of a bird's wing located close to the base of the primary feathers that, when raised and lowered, affect the airflow over the wing by increasing or decreasing lift during flight.

Alveolus
A term used to identify a small cavity, sac, or depression in the body. For example, the tiny cavities within the lungs or the depression in which a tooth sits.

Amnion
A delicate membrane that encloses an embryo of higher vertebrates (occurs in reptiles, birds, and mammals).

Amniote
Amniotes are a group of tetrapod vertebrates that lay eggs that are specially adapted to survive in a terrestrial environment.

Amphisbaenian
A wormlike (long and slender) reptile that has a short tail, and scales arranged in rings and is well-adapted to burrowing.

Amplexus
A mating position used by frogs and toads, in which the male holds the female with its front legs and fertilization usually takes place outside of the female's body and thus often requires a moist or aquatic environment.

Anastomosis
A branching and interconnecting network of tubes such as blood vessels, nerves, or leaf veins that branch and reconnect to form a plexus.

Animalia
The taxonomic group (kingdom) that includes organisms that are multicellular, eukaryotic, and heterotropic.

Annelida
The taxonomic group (phylum) of animals that includes segmented worms.

Antelope
The term antelope refers to approximately 90 species of even-toed ungulates that belong to the family Bovidae. Most antelope are native to Africa, though some species are native to Asia. The term antelope does not correspond to a single taxonomic group.

Antenna
A sensory aparatus (also referred to as a 'feeler') that is located on the head of an arthropod.

Antler
A bony structure that grows on the head of a deer. Contrasted with horns, antlers are often branched (whereas horns do not branch).

Apomorph
A new trait or structural feature that arises in an evolving lineage that is dissimilar from the ancestral line.

Aposematic
Characteristics (such bright coloration) that act as warnings to other animals (especially predators) and signal that an animal has defenses (for example, a poisonous frog that is brightly colored).

Arboreal
Pertaining to animals that are adapted to life in the tree tops, tree-dwelling.

Archean
The Archean Eon (3800 to 2500 MYA) was the time period in which the first lifeforms appeared on our planet. At that time, Earth was very different from what it is today. The atmosphere was composed of toxic gases such as methane and ammonia.

Arthropod
A taxonomic group of animals that includes spiders, crabs, insects, and centipedes and whose bodies posess pairs of jointed limbs and in most cases an exoskeleton or hard exterior covering.

Artificial Selection
A type of selection in which individuals are chosen (by a breeder) to mate and produce offspring with particular characteristics desired by the breeder.

Aspect Diversity
A measure of the variety of the physical appearances of species that live in the same habitat and are hunted by predators that use visual hunting skills to identify and capture prey.

Auriculars
A group of feathers that covers the side of a bird's head where the bird's ear openings are located.

Autonomic Nervous System
The part of the vertebrate nervous system that is made up of the motor neurons that innervate the animal's internal organs and that are in most cases not voluntarily controlled by the animal.

Autotroph
An organism that acquires energy from their environment (as opposed to acquiring energy via the ingestion of other organisms).

Aves
A taxonomic group (class) of vertebrates, also known commonly as 'birds', whose distinguishing characteristics include feathers, endothermy, and the production of amiotic eggs.

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