Introduction to Animals - Vocabulary

body plan

a term used to describe an animal's shape, symmetry, and internal organization

cephalization

the concentration of nerve tissue and sensory organs at the anterior end of an organism

internal fertilization

fertilization of an egg by sperm that occurs inside the body of a female

blastula

the stage of an embryo before gastrulation

coelom

a body cavity that contains the internal organs/fluid

phylogenic tree

a branching diagram that shows how organisms are related through evolution

gastrovascular cavity

a cavity that serves both digestive and circulatory purposes in some cnidarians/only one opening

bilateral symmetry

a condition in which two equal halves of a body mirror each other

exoskeleton

a hard, external, supporting structure that develops from the ectoderm

gills

a respiratory structure in aquatic animals that consists of many blood vessels surrounded by a membrane that allows for gas exchange

coelomates

an animal that has a body cavity in which the internal organs are located

pseudocoelomates

an animal that has a pseudocoelom, or false body cavity

acoelomates

an animal that lacks a coelom or body cavity

hermaphrodites

an organism that has both male and female reproductive organs

endoskeleton

composed of a hard material, such as bone, and is embedded within an animal

mesoderm

in an embryo, the middle layer of cells that gives ride to muscles, blood, and various systems

hydrostatic skeleton

in many invertebrates, the cavity that is filled with water and that has a support function

asymmetrical

irregular in shape; without symmetry

respiration

the exchange of oxygen and carbon dioxide between living cells and their environment

closed circulatory systems

the heart pumps blood through a system of blood vessels

open circulatory system

the heart pumps fluid through vessels that empty into spaces called sinuses

endoderm

the innermost germ layers of the animal embryo

ectoderm

the outermost of the three germ layers of an embryo that develops into the epidermis and epidermal tissues

external fertilization

the union of gametes outside the bodies of the parents, as in many fishes and amphibians

radial symmetry

when the body parts are arranged around a central axis