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