Phylum Cordata Introduction to the Fish Protochordates and Jawless Fishes

Fish Fish origins date back 500 million years according to the fossil record. There are 20,000 different species of fish (both marine and freshwater). They have a very diverse array of colors, shapes and sizes.

Cordate Characteristics Phylum Cordata is the most diverse phylum in the Animal Kingdom. The presence of a… Hollow, dorsal nerve cord Notochord (supports the nerve cord) Pharyngeal gill slits …characterize something as a chordate

Primitive Vertebrates The primitive cordates like the protochordates and jawless fish lack advanced structures of other vertebrates (including the fish) Vertebrates all have a skeleton, backbone, skull or advanced brain (protochordates do not have these)

Evolutionary Interest Protochordates are of interest to scientists because they are believed to be the link between invertebrates and vertebrates.

Tunicates Tunicates are often referred to as sea squirts because they squirt water when touched. Have incurrent and excurrent siphons through which water enters and exits Individuals are hermaphrodites, but do not fertilize themselves. Fertilization and development are external since gametes are shed into the water.

Tunicate

T U N I C A E

T U N I C A E

Lancelets Lives buried in the sand with its head sticking out filtering plankton out of the water. Separate sexes – fertilization and development are external.

L A N C E T

Lancelet

L A N C E T

Acorn Worm Burrow in the sand of the intertidal and subtidal zone where they feed on the organic materials in the sand.

Acorn Worm

Acorn Worm Cast

Jawless Fish First fish Adults retain their notochord for support of their body. Both Sea lamprey and hagfish live as parasites and use their circular rows of teeth to burrow into dead and dying animals.

Lamprey Mouth

Hagfish

Hagfish Mouth