Chorodates

notochord

fexible rod-like structure extending the length of the body axis for muscle attachment, displaced by vertebrea, some remain between vertebrea

dorsal hollow nerve cord

anterior end become enlarged = brain, goes throug the spinal chord to the skull

pharyngeal gill silts or pouches

perforated slits-like openings that lead from the pharyngeal cavity to the outside

postanal tail

together with musculature and the stiffening of notochord provides motility (tail)

Subphylum Urochordata (tunicates)

filter-feeding marine animald that use a perforated pharynx as a net like structure

Subphylum Cephalochordata (amphioxus)

small marine organisms, myomers occure allong both sides of the body

Ostracoderms

had cartilaginour endoskeleton, radiated and then went extinct during the Silurain, few surviver into the Devonian

Subphylum Vertebrata (vertebrates)

chorodates with a “backbone” (hagfish and lampreys)

Superclass Agnatha

jawless fishes, hagfish, and lamprey, absence of jaws, cartilage skeleton

Class Myxini

hagfishes, marine specise, bottom-dwelling scavengers, slime glands (defensive and knotting behavior), rudimentary crainium

Class Cephalaspiodomorphi

lampreys,