Chordata 1, Lecture Notes

All chordates possess these 5 unique characteristics at some point in their life(even if they disappear later on)-a notochord-single, dorsal hollow nerve cord-pharyngeal ("gill") pouches/slits-post anal tail-pharyngeal endostyle/ thyroid

Evidence of evolution, early embryos of diverse groups share many features, as development proceeds, embryonic forms diverge and become more similar to adults of their own species

Flexible rod-like structure that extends the length of the body and serves as an axis for muscle attachment

Cartilaginous or bony vertebrae in jawed vertebrates

-a single hollow (tube like) nerve cord-dorsal to alimentary canal and the notochord-in vertebrates the anterior end becomes enlarged to form the brain, the remainder is the spinal cord.

Anterior end becomes enlarged to form the brain, the remainder is spinal cord

-slit like opening connecting the pharyngeal cavity and the outside environment -in aquatic chordates, become gills-in tetrapods, they become part of throat and ear cavity

-Ciliated grooves in floor of pharynx that traps food-present in protochordates and lemprey larvae where the pharynx evolved as a filter-feeding apparatus-in more derived adult lamprey & vertebrates: homologous to the thyroid

Filter feeding apparatus

-posterior to anus-associated with somatic musculature-facilitates motility/ propulsion in aquatic environments

Subphylum; tunicates, ascidians, sea squirts-only posses the 5 chordate characteristics as a tadpole larva-sessile adults have lost all chordate characteristics except pharyngeal gill slits & endostyle-filter feeders via pharynx

Only as a tadpole larva

-Pharyngeal gills slits and endostyle

Filter feeders via pharynx

When the swimming larvae becomes sexually mature