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Animals that lack a backbone


Animals that possess a backbone


An organism possesses spherical symmetry if it can be cut into two identical halves by any cut that runs through the organism's center

Spherical symmetry

An organism possesses radial symmetry if it can be cut into two identical halves by any longitudinal cut through its center

Radial symmetry

An organism possesses bilateral symmetry if it can only be cut into two identical halves by a single longitudinal cut along its center which divides it into right and left halves

Bilateral symmetry

An outer layer of cells designed to provide protection


The jellylike substance that separates the epidermis from the inner cells in a sponge


Flagellated cells that push water through a sponge

Collar cells

Cells that move using pseudopods and perform different functions in different animals


A cluster of cells encased in a hard, spicule-reinforced shell


The sessile, tubular form of a cnidarian with a mouth and tentacles at one end and a basal disk at the other


A free-swimming cnidarian with a bell-shaped body and tentacles


Animal tissue consisting of one or more layers of cells that have only one free surface, because the other surface adheres to a membrane or other substance


The jellylike substance that separates the epithelial cells in a cnidarian


Small capsules that contain a toxin which is injected into prey or predators


Organs that produce sperm


Organs that produce eggs


The end of an animal that contains its head

Anterior end

The end of an animal that contains its tail

Posterior end

A system designed to transport food and other necessary substances throughout a creature's body

Circulatory system

A system of sensitive cells that respond to stimuli such as sound, touch, and taste

Nervous system

Masses of nerve cell bodies

Ganglia (singular: ganglion)

Possessing both the male and the female reproductive organs


The ability to regrow a missing part of the body


A sheath of tissue that encloses the vital organs of a mollusk, makes the mollusk's shell, and performs respiration


A tough, multilayered structure secreted by the mantle, generally used for protection, but sometimes for body support


A hump that contains a mollusk's heart, digestive, and excretory organs

Visceral hump

A muscular organ that is used for locomotion and takes a variety of forms depending on the animal


An organ covered with teeth that mollusks use to scrape food into their mouths


An organism with a single shell


An organism with two shells


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