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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