Clade Chordata

Body System

Body Structure

5 chordate characteristics

Dorsal notochord

Dorsal, hollow nerve cord

Pharyngeal gill slits

Muscular post-anal tail

Endostyle or thyroid gland

Taxonomic Division

Phylum Cephalochordata (lancelets)

Adult stage bears all five chordate characteristics and NO larval stage

Phylum Tunicata (sea squirts, tunicates)

Sac-like,filter-feeding chordates with a tadpole larva that has ALL five chordate characteristics, lack a cranium

Phylum Vertebrata

Chordates that have a cranium surrounding the brain

Lancelets filter feed and have a complete digestive

Lancelets have a closed circulatory system

Lancelets do excretion and respiration by diffusion over the body surface

Lancelets have a dorsal hollow nerve cord

Reproduction and Development

Lancelets are dioecious with external fertilization

Urochordates are monoecious with an ovary and testis within the coelom... with external fertilization. The fertilized eggs develop into tadpole larvae

Urochordates have a small "brain" (neural ganglion) connected to various other ganglia by nerve cords

Urochordates have no respiratory or excretion organs -- individual cells exchange gases and nitrogenous waste with the water inside or outside the body by diffusion