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