Apologia Biology, 2nd Edition, Module 11

invertebrates

animals that lack a backbone

vertebrates

animals that possess a backbone

spherical symmetry

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

radial symmetry

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

bilateral 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

epidermis

an outer layer of cells designed to provide protection

mesenchyme

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

collar cells

flagellated cells that push water through a sponge

amoebocytes

cells that move using pseudopods and perform a variety of functions in animals

gemmule

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

polyp

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

medusa

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

epithelium

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

mesoglea

the jelly-like substance that separates the epithelial cells in a cnidarian

nematocysts

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

testes

organs that produce sperm

ovaries

organs that produce eggs

anterior end

the end of an animal that contains its head

posterior end

the end of an animal that contains its tail

circulatory system

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

nervous system

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

ganglia

masses of nerve cell bodies

hermaphroditic

possessing both the male and the female reproductive organs

regeneration

the ability to regrow a missing part of the body

mantle

a sheath of tissue that encloses the vital organs of a mollusk, secretes its shell, and performs respiration

shell

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

visceral hump

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

foot

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

radula

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

univalve

an organism with a single shell

bivalve

an organism with two shells