The Prechordates Phyla that have some chordate features but not all Considered to be possible ancestors to the phylum Chordata

Phylum Chaetognatha Arrow worms Approximately 70 species; 1-10 cm long All marine, free-living, planktonic bilaterally symmetrical, as are all of the rest of the phyla

Phylum Chaetognatha Arrow worms body of three regions: head, trunk, tail has lateral and caudal fins has circumesophogeal ganglia

Phylum Chaetognatha Arrow worms no circulatory system, excretory system, respiratory skeleton is hydrostatic type are hermaphroditic; with cross-fertilization, and internal are carnivorous - predators of plankton

Phylum Hemichordata (the acorn worms) about 100 species, all marine, 0.5 cm - 2 m benthic (live on the bottom) and free living solitary or colonial vermiform- elongate

Phylum Hemichordata (the acorn worms) body in three parts; proboscis, collar and trunk are gill slits for respiration no post-anal tail

Phylum Hemichordata (the acorn worms) have free living larvae called tornaria Resemble echinoderm larvae

Phylum Hemichordata (the acorn worms) primarily feeding on detritus and microscopic organisms have circulatory system; two main blood vessels and a central sinus (heart) sexes are separate; fertilization is external