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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

T

E

T

U

N

I

C

A

T

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

L

E

T

Lancelet

L

A

N

C

E

L

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