phylum cordata introduction to the fish protochordates and jawless fishes

Phylum CordataIntroduction 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