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Chapter 18
Fishes
Characteristics
• Phylum: Craniata
(describes the skull that
surrounds their brain
• Much evolution occurred
in freshwater
• Much evolution involved
the movement of fish
between fresh and
marine environments
• Over 41% of fish live in
freshwater even though
only small percentage of
the Earth’s water
resources is freshwater
Subphylum Hyperotreti: Hagfishes
• 20 species
• Heads are supported by
cartilage and brains enclosed
in a fibrous sheath
• Retain a notochord
• 4 pairs of sensory tentacles
surrounding their mouths
• Cold water marine habitats
• Most primitive group in the
craniata
• Live buried in the sand and
mud
• Feed off of soft bodied
invertebrates and scavenge
dead and dying fish
• Slimy skin
Subphylum Vertebrata:
Ostracoderms
• Extinct agnathans
• Had bony armor as a
defense
• Bottom dwellers
• Filter feeders
Subphylum Vertebrata: HyperoartiaClass Cephalaspidomorphi
• Lampreys
• Found in freshwater and
marine environments
• Prey on other fish and
their larvae as filter
feeders
• Mouth of an adult
lamprey is suckerlike with
lips that have sensory
attachments
• Have salivary glands with
anticoagulant secretions
and feed mainly on the
blood of their prey
Lampreys
• Adult lampreys live in the
ocean or the Great lakes, at
the end of their lives they
migrate to freshwater to spawn
• They build spawning nests in
shallow water, a female
attaches to a rock with her
mouth, male use their mouth to
attach to the female head and
wrap themselves around the
female
• Eggs are shed in batches and
fertilized externally and then
covered in sand
Gnathostomata
1. 2 important evolutionary
developments
–
–
2.
3.
Jaws: allowed for more
efficient gill ventilation
Paired appendages:
used to counteract the
tendency to roll during
locomotion and control
the pitch of the the
swimming fish
2 classes: cartilaginous
and bony fish
Contain the armored fish
which are extinct and
acanthodians which are
also extinct