Blastula

early animal embryo consisting of a hollow ball of cells

Gastrula

advanced animal embryo consisting of two or more tissue layers

Invertebrate

animal with no backbone

Vertebrate

animal with a backbone

Eumetazoa

animals with tissues

Parazoa

animals with no tissues

Bilateral symmetry

body symmetry where the body can be divided into two identical halves

Radial symmetry

body symmetry where the body can be divided into multiple similar parts

Cephalization

concentration of sensory organs and brain at the head

Ectoderm

outer tissue layer, becomes skin and nervous system

Endoderm

inner tissue layer, becomes digestive system

Mesoderm

middle tissue layer, becomes muscles and circulatory system

Deuterostome

organisms that develop “anus first”

Protostome

organisms that develop “mouth first”

Coelom

body cavity