The document discusses early fish evolution, including jawless fish like hagfish and lampreys. It describes key characteristics of hagfish, including that they have no backbone but are still considered vertebrates. It then discusses different classes of jawless fish like lampreys and ostracoderms, which were early armored fish. Placoderms followed as the first jawed fish.

1. Early Fish Evolution
• Phylum Chordata
• Subphylum Urochordata

3. • Phylum Chordata
• Subphylum Cephalochordata

6. Fish History
• Phylum Chordata
• Subphylum Vertebrata

7. Jawless Fishes
Class: Myxini - Hagfishes
Class: Cephalaspidomorphi – Lampreys
Class: Ostracodermi – Ostracoderms,
jawless fishes with plate covered skin

8. Hagfish are very
primitive vertebrates.
Primarily scavengers,
they live near the ocean
floor where they
consume dead fish and
marine worms.

9. Hagfish have no paired appendages or backbone
yet they are considered vertebrates. They have a
cartilaginous “shelf” upon which their brain rests.
Biologists consider this the beginnings of the
skull.

10. Hagfish have no jaws.
Their tongue has two
rows of rasp-like
structures that enable
them to scrape at their
food.
A row of sensory
tentacles surround the
hagfish’s mouth.

11. Hagfish are sometimes
called “knot fish”
because they are able
to tie themselves into
knots. They do this to
rid their skin of excess
slime and to gain
leverage so that they
can enter the anus of
dead fish upon which
they scavenge.

12. Agnathan Fish
Class: Cephalaspidomorphi
Lampreys

18. Brook Lamprey – an
Ohio native.
This species only attains a length of about six
inches. It spends several years as a larva
burrowed in the sediment at the bottom of a
stream where it filter feeds.
After metamorphosis, the adults do not feed.
They simply migrate to a suitable breeding site
in their stream, reproduce, then die.

19. The Silver Lamprey is another Ohio native. Adults of
this species are parasitic upon fish. It is uncommon but
does occur in the Ohio River and some of its larger
tributaries.
Scientists very rarely are able to collect this fish. Only
seven have been collected in Ohio in the past 30 years.
Evidence of its presence is occasionally seen when a
fisherman catches a fish with deep wounds caused by the
silver lamprey. Adults attain a maximum length of
about 8 to 10 inches.

20. The Sea Lamprey is not native to Ohio, but it has been accidentally
introduced by ocean going ships. In the Atlantic Ocean, this species
may attain a length of 3 feet, but in Lake Erie it seldom grows to more
than 2 feet.
It has caused tremendous damage to the commercial fishing industry.
It has all but eliminated the Lake Trout, a large fish that was harvested
from Lake Erie by the thousands of tons as recently as the 1930’s. By
the 1960’s only about 400 pounds of Lake Trout were harvested from
the same waters. Government agencies spend tens of thousands of
dollars annually in an attempt to control this species.

22. The lamprey’s
jawless mouth is
able to form a
suction on the body
wall of its host fish
enabling it to use
the rasps on its
tongue to scrape
open wounds.
The blood, and fluids that ooze from the wound are swallowed
by the lamprey as its source of food. When full, it releases its
hold. The host fish usually heals, but in Lake Erie, where
sufficiently large fish are rare, scores of Sea Lampreys may
attached to a single fish. Lake Trout populations have suffered.

24. This experiment was conducted in an aquarium. Newly
metamorphosed Sea Lampreys were released with Lake
Trout. They instantly attached to the trout and started
feeding.

25. The grasp of these small Sea Lampreys on this Lake Trout
are so strong that they don’t release, even when removed
from the water.

26. This Lake Trout has been stuffed and mounted with a Sea
Lamprey parasitizing it. Lake Trout from the great lakes
often have up to ten Sea Lampreys on them and hundreds
of old wounds. After being so heavily parasitized, most of
the trout will die.

27. This Lake Trout has
just had a Sea
Lamprey pulled
from its body wall.
The wound created by the lamprey is quite evident in
this photograph. Fish usually recover from one or two
wounds, but oozing blood attracts more lampreys. If
they find the wounded fish, more lampreys will attach.

28. This wildlife officer is holding
two Lake Trout that were severely
wounded by Sea Lampreys in
Lake Erie.
Efforts to eliminate Sea Lampreys
have failed but measures to limit
their populations have been
successful. Unfortunately they
are controlled by chemical means.
TFM, the most successful
lampricide has grim effects on
other species of aquatic animals.
TFM causes no harm to adult
lampreys. It kills the filter
feeding larvae.

30. A lamprey larvae looks
remarkably similar to a
Lancelet (Amphioxus).
When first discovered,
scientists considered the
lamprey larvae to be a new
species of Lancelet and they
gave them the genus name
Ammocoetes. Eventually they learned that these were lamprey
larvae. Today Lancelets are the evolutionary ancestors of
lampreys based on developmental, ecological, and anatomical
similarities between larval lampreys and Lancelets. Like
Lancelets, ammocoetes live burrowed in the mud, filter feeding on
protozoans and organic matter. Today the word ammocoete is
used as the term for any lamprey larva.

31. Fish History
• Phylum Chordata
• Subphylum Vertebrata
• Class Ostracodermi

32. Class: Ostracodermi - The Ostracoderms
These jawless fishes had paired fins, a bony spine, and
heavy, protective, bony armor that covered their skin.

37. Ostracoderms are only
known as fossils today.
However they once ruled the
seas for nearly 100 million
years.
They probably got their food
by sucking up the sediments
from the sea floor and
digesting any organic
material from it.
Scientists speculate that the Ostracoderms’ heavy armor made
them too slow to compete as more advanced fishes evolved.
Consequently they eventually became extinct.

38. Fish History
• Phylum Chordata
• Subphylum Vertebrata
• Class Placodermi

39. Class: Placodermi - this fossilized fish represents the
first vertebrate animal to have evolved jaws.
Similar to Ostracoderms, the Placoderms were large, heavy,
and covered with bony plates. Their jaws, however allowed
them to hunt, and consequently they pushed the Ostracoderms
into extinction.
This Placoderm fish
fossil was discovered in
northern Ohio and is
on exhibit at the
Cleveland Museum of
Natural History.

42. The word Agnatha used to be a Class that included
lampreys and hagfishes, boneless, jawless fishes.
However they are divided into the Classes: Myxini
and Cephalaspidomorphi today.
Although it isn’t a taxonomic term, the word
Agnatha is still used by biologists to describe any
jawless vertebrates.
A – without gnath – jaws

43. Gnathostomes are vertebrate animals that do
have jaws.
Gnath – jaw
Stome – hole or opening
Gnathostome means opening (mouth) with
jaws.