The Prechordates

• Phyla that have some chordate features but not all

• Considered to be possible ancestors to the phylum Chordata

Phylum ChaetognathaArrow worms

• Approximately 70 species; 1-10 cm long

• All marine, free-living, planktonic

• bilaterally symmetrical, as are all of the rest of the phyla

• body of three regions: head, trunk, tail

• has lateral and caudal fins

• has circumesophogeal ganglia

Phylum ChaetognathaArrow worms

• no circulatory system, excretory system, respiratory

• skeleton is hydrostatic type

• are hermaphroditic; with cross-fertilization, and internal

• are carnivorous - predators of plankton

Phylum ChaetognathaArrow worms

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

• 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 

Phylum Hemichordata (the acorn worms)