Dorsal, Ventral, Anterior, and Posterior

• Dorsal - top (back)
• Ventral - bottom (front)
• Anterior - "headness"
• Posterior - "tailness"

Ectoderm

• outside tissue layer
• gives rise to skin and nervous system

Endoderm

• inside tissue layer
• forms lining of the gut and digestive organs

Mesoderm

• middle tissue layer
• becomes muscles, skeleton, connective tissue, and circulatory structures

Diploblastic

two tissue layers

(ectoderm and endoderm)

Triploblastic

three tissue layers

(ectoderm/endoderm/mesoderm)

Coelom

body cavity in addition to a digestive cavity

Acoelomate

no body cavity

Pseudocoelomate

• false body cavity located between endoderm and mesoderm
• lack epithelial lining (no peritoneum)
• hemocoel - filled with blood

Coelomate

• true body cavity
• located within mesoderm
• lined with epithelial tissue (peritoneum)
• internal organs suspended by double layers of mesoderm known as mesentery
• fluid filled

Blastopore

opening in the gastrula stage of an embryo

Protostome

• mouth forms at or near blastopore
• coelom forms by splitting of the mesoderm
• spiral cleavage
• more primitive

Deuterostome

• anus forms at or near blastopore
• mouth forms elsewhere
• coelom formed by out-pouching of the embryonic gut
• radial cleavage
• more advanced

Dioecious

two separate sexes

Monoecious

one individual but has both male and female reproductive organs (hermaphrodite)

Absent Circulatory System

uses diffusion and osmosis instead

Open Circulatory System

has a heart but no vessels

Closed Circulatory System

has a heart and vessels

Cephalization

• aggregation of sensory cells/nerve cells (ganglion)
• located in anterior portion

Incomplete Digestive System

one opening

Complete Digestive System

two openings

(mouth and anus)

No Respiratory Structures

uses simple diffusion

Respiratory Structures Present

gills or lungs

No Excretory Structures

uses simple diffusion

Primitive Excretory Structures

flame cells, nephridia, or malpighian tubules

Complex Excretory Structures

kidney

Asymmetry

no shape or form

Radial Symmetry

arranged around a central point and can be divided along many planes

Bilateral Symmetry

cut down middle and the right and left sides are mirror images of each other