The document discusses the evolution of early vertebrates from jawless fishes to jawed fishes. It describes the characteristics of modern and extinct Agnathans (jawless) like hagfish and lampreys, including their filter feeding and parasitic behaviors. Chondrichthyes (cartilaginous fishes) such as sharks, rays and chimaeras are discussed next, noting they lack bone and have placoid scales and advanced sensory systems. Key trends in vertebrate evolution included the development of the vertebral column, jaws, paired fins, and gills.

1. COMPARATIVE
VERTEBRATE ANATOMY
Agnatha and Chondrichthyes

2. Agnathans and Chondrichthyes
*

3. Agnathans
 Agnathans = Group that includes the
jawless vertebrates with a fossil record
extending back over 500 million years
that is represented today by the living
hagfishes and lampreys.

4. Agnathans
Hagfish “Myxine”
(Myxiniformes)
Hagfish
Lamprey
“Petromyzon”
(Petromyzontiformes)
*Both possess a
Cyclostome (round Lamprey
mouth).

5. Hagfishes
 There are 45 living species.
 Possess integumentary glands that
secrete mucus for protection. (Gives
them the common name “Slime Hags”.)
 Similar to amphioxus, tunicates, and
echinoderms because they lack jaws,
paired appendages, and bone.
 Lack vertebrae.*

6. Hagfishes, Cont.
 Remain Isosmotic with sea water.
 Are Serially Hermaphroditic (are male
when newly matured but become
female). [Other organisms may start as
female and become male.]
 Oviparous reproduction.

7. Lampreys
 There are approximately 40 living species.
 Feed by attaching the buccal funnel with
keratinized “teeth” to prey and secreting
an anticoagulant onto the tissue.
 Most species are Anadromous. (Reside in
the ocean as adults and return to rivers to
spawn).

8. Lampreys, Cont.
 Some species remain in fresh water their
entire lives.
 Adults die after spawning.
 Eggs hatch into Ammocoete larvae.
 Larvae are filter feeders that trap food in
a mucus-like secretion which comes
from the subpharyngeal gland.

9. Extinct Jawless Vertebrates
 There are many groups of extinct jawless
vertebrates according to fossil records.
 Many of these species possessed body
scales, shields, or plates.
 Also, many species possessed
“acellular” bone, which differs from
typical vertebrate bone by lacking
enclosed cells.

10. Gnathostomes
 Gnathostomata = All of the jawed
vertebrates.
 Also possess:
- Paired Nostrils
- Five Gill Slits
- Articulated Gill Arches
- Two Sets of Paired Appendages
- Three Semicircular Ducts in the Ears

11. Gnathosomtes, Cont.
 Considered the dominant vertebrates.
 Include:
- Placoderms (plate; skin) (heavily
armored) [Extinct.]
- Chondrichthyes (cartilaginous fishes)
- Etc. (every other vertebrate group)
[Group of Placoderms and Chondrichthyes
together is called Elasmobranchiomorphi.]

12. Evolution of Jaws

13. Chondrichthyes
 Chondrichthyes = The cartilaginous
fishes, including the sharks, skates,
rays, and chimaeras.
- Elasmobranchii includes the sharks,
skates, and rays.
- Holocephili includes the chimaeras.

14. Chondrichthyes, Cont.
Chimaera
(Ghost Shark)
*From Wikipedia

15. Chondrichthyes, Cont.
 There are approximately 800 living
species.
 Lack true bone and dermal plates
although the cartilage is calcified.
 Possess Placoid Scales that may be
remnants of body armor.
 May be Oviparous, Ovoviparous, or
Viviparous.

16. Chondrichthyes, Cont.
 Fertilization of eggs is internal and males
possess Claspers to facilitate
copulation.
 Lack swim bladders, but produce lipids
in the liver to increase bouyancy.
 Possess electroreceptors called
Ampullae of Lorenzini to locate prey.

17. Chondrichthyes, Cont.
 Differences in Holocephali:
- Scales are mostly absent.
- Upper jaw is firmly attached to the
cranium.
- Gills are covered by a flap called an
Operculum.

18. Evolution of the Fishes

19. Conclusions
 The following trends occurred in the
evolution of vertebrate lineages.
– Vertebral Column
– Jaws
– Paired Appendages (fins)
– Respiration by Gills