COMPARATIVE COMPARATIVE VERTEBRATE ANATOMYVERTEBRATE ANATOMY

Agnatha and ChondrichthyesAgnatha and Chondrichthyes

Agnathans and Chondrichthyes

*

AgnathansAgnathans

AgnathansAgnathans = Group that includes the = Group that includes the

jawless vertebrates with a fossil record jawless vertebrates with a fossil record

extending back over 500 million years extending back over 500 million years

that is represented today by the livingthat is represented today by the living

hagfisheshagfishes and and lampreyslampreys..

AgnathansAgnathans

HagfishHagfish “Myxine” “Myxine”

(Myxiniformes)(Myxiniformes)

LampreyLamprey “Petromyzon”“Petromyzon”

(Petromyzontiformes)(Petromyzontiformes)

*Both possess a*Both possess a

CyclostomeCyclostome (round (round

mouth).mouth).

Hagfish

Lamprey

HagfishesHagfishes

There are 45 living species.There are 45 living species. Possess integumentary glands that Possess integumentary glands that

secrete mucus for protection. (Gives secrete mucus for protection. (Gives

them the common name “Slime Hags”.)them the common name “Slime Hags”.) Similar to amphioxus, tunicates, and Similar to amphioxus, tunicates, and

echinoderms because they lack jaws, echinoderms because they lack jaws,

paired appendages, and bone.paired appendages, and bone. Lack vertebrae.*Lack vertebrae.*

Hagfishes, Cont.Hagfishes, Cont.

Remain Remain IsosmoticIsosmotic with sea water. with sea water. Are Are Serially HermaphroditicSerially Hermaphroditic (are male (are male

when newly matured but become when newly matured but become

female). [Other organisms may start as female). [Other organisms may start as

female and become male.]female and become male.] Oviparous reproduction.Oviparous reproduction.

LampreysLampreys

There are approximately 40 living species.There are approximately 40 living species. Feed by attaching the buccal funnel with Feed by attaching the buccal funnel with

keratinized “teeth” to prey and secreting keratinized “teeth” to prey and secreting

an anticoagulant onto the tissue.an anticoagulant onto the tissue. Most species areMost species are AnadromousAnadromous.. (Reside in (Reside in

the ocean as adults and return to rivers to the ocean as adults and return to rivers to

spawn).spawn).

Lampreys, Cont.Lampreys, Cont.

Some species remain in fresh water their Some species remain in fresh water their

entire lives.entire lives. Adults die after spawning.Adults die after spawning. Eggs hatch into Eggs hatch into AmmocoeteAmmocoete larvae. larvae. Larvae are filter feeders that trap food in Larvae are filter feeders that trap food in

a mucus-like secretion which comes a mucus-like secretion which comes

from the subpharyngeal gland.from the subpharyngeal gland.

Extinct Jawless Vertebrates Extinct Jawless Vertebrates

There are many groups of extinct jawless There are many groups of extinct jawless

vertebrates according to fossil records.vertebrates according to fossil records. Many of these species possessed body Many of these species possessed body

scales, shields, or plates.scales, shields, or plates. Also, many species possessed Also, many species possessed

“ “acellular” bone, which differs from acellular” bone, which differs from

typical vertebrate bone by lacking typical vertebrate bone by lacking

enclosed cells.enclosed cells.

GnathostomesGnathostomes

GnathostomataGnathostomata = All of the jawed = All of the jawed

vertebrates.vertebrates. Also possess:Also possess:

- Paired Nostrils- Paired Nostrils

- Five Gill Slits- Five Gill Slits

- Articulated Gill Arches- Articulated Gill Arches

- Two Sets of Paired Appendages- Two Sets of Paired Appendages

- Three Semicircular Ducts in the Ears- Three Semicircular Ducts in the Ears

Gnathosomtes, Cont.Gnathosomtes, Cont.

Considered the dominant vertebrates.Considered the dominant vertebrates. Include: Include:

- - PlacodermsPlacoderms (plate; skin) (heavily (plate; skin) (heavily

armored) [Extinct.]armored) [Extinct.]

- - ChondrichthyesChondrichthyes (cartilaginous fishes) (cartilaginous fishes)

- Etc. (every other vertebrate group)- Etc. (every other vertebrate group)

[Group of Placoderms and Chondrichthyes [Group of Placoderms and Chondrichthyes

together is called Elasmobranchiomorphi.]together is called Elasmobranchiomorphi.]

Evolution of JawsEvolution of Jaws

ChondrichthyesChondrichthyes

ChondrichthyesChondrichthyes = The cartilaginous = The cartilaginous

fishes, including the sharks, skates, fishes, including the sharks, skates,

rays, and chimaeras.rays, and chimaeras.

- - ElasmobranchiiElasmobranchii includes the sharks, includes the sharks,

skates, and rays.skates, and rays.

- - HolocephiliHolocephili includes the chimaeras. includes the chimaeras.

Chondrichthyes, Cont.Chondrichthyes, Cont.

*From Wikipedia

Chimaera (Ghost Shark)

Chondrichthyes, Cont.Chondrichthyes, Cont.

There are approximately 800 living There are approximately 800 living

species.species. Lack true bone and dermal plates Lack true bone and dermal plates

although the cartilage is calcified.although the cartilage is calcified. Possess Possess Placoid ScalesPlacoid Scales that may be that may be

remnants of body armor.remnants of body armor. May be Oviparous, Ovoviparous, or May be Oviparous, Ovoviparous, or

Viviparous.Viviparous.

Chondrichthyes, Cont.Chondrichthyes, Cont.

Fertilization of eggs is internal and males Fertilization of eggs is internal and males

possess Claspers to facilitate possess Claspers to facilitate

copulation.copulation. Lack swim bladders, but produce lipids Lack swim bladders, but produce lipids

in the liver to increase bouyancy.in the liver to increase bouyancy. Possess electroreceptors called Possess electroreceptors called

Ampullae of LorenziniAmpullae of Lorenzini to locate prey.to locate prey.

Chondrichthyes, Cont.Chondrichthyes, Cont.

Differences in Differences in HolocephaliHolocephali::

- Scales are mostly absent.- Scales are mostly absent.

- Upper jaw is firmly attached to the - Upper jaw is firmly attached to the

cranium.cranium.

- Gills are covered by a flap called an - Gills are covered by a flap called an

OperculumOperculum..

Evolution of the FishesEvolution of the Fishes

ConclusionsConclusions

The following trends occurred in the The following trends occurred in the evolution of vertebrate lineages.evolution of vertebrate lineages.

– Vertebral ColumnVertebral Column

– JawsJaws

– Paired Appendages (fins)Paired Appendages (fins)

– Respiration by GillsRespiration by Gills