Blastula
hollow ball of cells that gives rise to all the tissues and organs of an adult body
Ectoderm
in animals, the outer layer of embryonic tissue from which the skin and nervous system develop
Endoderm
inner layer of embryonic tissue from which the digestive organs develop in animals
Mesoderm
middle layer of embryonic tissue in animals from which the skeleton and muscles develop
Body Plan
An animal's shape, symmetry, and internal organization
Asymmetrical
irregular in shape
Radial Symmetry
arrangement of body parts around a central axis
Bilateral Symmetry
arrangement of body parts so there are distinct left and right halves that mirror each other
Cephalization
in bilaterally symmetric animals, the development of a head end with a concentration of nerves and sensory structures
Coelom
fluid-filled body cavity that forms between the body wall and the digestive tract
Acoelomate
an animal that lacks a coelom, or body cavity
Pseudocoelomate
animal with a body cavity located between the endoderm and the mesoderm
Coelomate
animal with a body cavity located entirely within the mesoderm
Phylogenetic Tree
branching diagram that shows how animals are related through evolution
Gastrovascular Cavity
a digestive cavity with only one opening; found in simple animals
Respiration
simultaneous uptake of oxygen and release of carbon dioxide, by the lungs, gills, or through the skin
Gill
extremely thin projection of tissue rich in blood vessels that in the site of gas exchange in aquatic and a few terrestrial animals
Open Circulatory System
system in which blood leaves the blood vessels and bathes the body's tissues
Closed Circulatory System
system in which the blood does not leave the blood vessels and materials diffuse across the walls of the vessels
Hydrostatic Skeleton
support structure that consists of water contained under pressure in a closed cavity
Exoskeleton
hard external covering of some invertebrates
Endoskeleton
an internal skeleton composed of a hard material, such as bone
Hermaphrodite
an organism that contains both the male and female reproductive organs (testes and ovaries)
External Fertilization
union of egg and sperm occuring outside the body of either parent
Internal Fertilization
fertilization that occurs within the body of the female parent