Phylum Chordata

Phylum Chordata common characteristics segmented muscles  ventral heart  complete digestive system Five defining chordate characteristics  pharyngeal gill slits  dorsal, hollow nerve cord post anal tail endostyle/thyroid gland  notochord

Body Structure pharyngeal slits & atriopore Notochord with myomeres post-anal tail dorsal, hollow nerve cord

Subphylum Urochordata (Tunicates) “tail string” all are filter feeders sessile & pelagic; solitary & colonial tadpole-like larva Adult Larva

Three Classes Ascidiacea Larvacea Thaliacea

Class Ascidiacea “sea squirts” u-shaped gut, with incurrent oral and excurrent atrial siphons large central chamber (atrium)

Larval Ascidean

Class Thaliacea

Class Larvacea

Subphylum Cephalochordata “head string” Lancelets (Amphioxus) burrow into sand & shell gravels filter feeders

Closed Circulatory System flow pattern similar to fishes no “heart” peristaltic contractions of blood vessels

Filter Feeders

larval notochord replaced by vertebral column in adults Phylum Chordata Subphylum Vertebrata larval notochord replaced by vertebral column in adults dorsal nerve cord pharyngeal gill slits

Trends in Vertebrate Evolution Living Endoskeleton Pharynx and Efficient Respiration Advanced Nervous System Paired Limbs

Early Chordata Fossils Pikaia Resembles Amphioxus Distinct notochord Chevron shaped muscle