Phylum Chordata

Nonvertebrate chordates Fishes Amphibians Reptiles Birds Mammals Invertebrate ancestor Chordate Cladogram

All chordates at sometime during their life history have: a notochord: a dorsal supporting rod located dorsally just below the nerve cord; it provides support and is replaced by the vertebral column in vertebrates a dorsal hollow nerve cord: a fluid-filled canal; spinal cord is protected by vertebrae pharyngeal gill pouches: openings that function in feeding, gas exchange, or both

Chordates that are not vertebrates Subphylum Urochordata contains 1,250 species

Tunicates (Sea Squirts), Larvae The larvae of tunicates resemble the ancestral chordate. It has all three chordate characteristics and looks like a tadpole. The free-swimming larva develops into a sessile, filter-feeding adult. Adult The adult has a thick-walled body sac and an incurrent siphon and an excurrent siphon. Gill slits are the only chordate feature retained by the adult form. In some tunicates, the adult form may have been lost. These animals retained the larval form as adults. Vertebrates may have evolved from forms like these.

Subphylum Cephalochordata

 23 species of lancelets are in the genus Branchiostoma  elongated, lance-shaped body resembles the lancelet, a two-edged surgical knife  inhabit shallow coastal waters; they lie partly buried in sandy substrates and filter feed  Lancelets retain the three chordate characteristics as an adult  notochord extends from head to tail  segmented muscles and their  dorsal hollow nerve cord

Vertebrate Chordates Subphylum Vertebrata Animals with a vertebra column.