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Unit 8.2

Class Agnatha, Chondrichthyes, &

Osteichthyes

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The Vertebrates

Subphylum Vertebrata

• All vertebrates have a backbone, cranium, and spinal cord.

• All contain paired-mass muscular systems

• Sensory organs, especially the eyes, are concentrated anteriorly & there is pronounced cephalization.

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Fig. 48.8

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Superclass Agnatha• First appeared in the

Cambrian period about 500 mya

• No jaws• No paired appendages• Notochord provides primary

protection and support for nerve cord

• Fertilization & development are carried out externally

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Ostracoderms• Earliest vertebrates• Evolved during the

early Paleozoic era• Jawless - fed by filter

feeding.• Covered in armor

made of bony plates.• Totally extinct group

of fish (P-T extinction)

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Hagfish and Lampreys

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Class Cephalaspidomorphi

Lamprey

Ectoparasites

Lampreys

• Live mostly in coastal and fresh waters.

• Always return to fresh water to reproduce.

• Larvae show low tolerance for high temperatures. Thus, they are not found in the tropics.

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Lampreys• Begin life as burrowing,

toothless larvae.• After 5 to 7 years, they

undergo an incredible metamorphosis to turn into pelagic, adult parasites.

• Attach to fish, secrete an anticoagulant, and feed on blood.

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Class MyxiniHagfish

Hagfish• The only animals to

have a skull, but not a vertebral column.

• Have worm-like hearts. 1 main brachial pump and 3 auxiliary hearts.

• Able to change sex to meet population needs.

• No larval stage

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Hagfish• Able to secrete copious

amounts of thick slime to deter or evade predation.

• Clean off the slime by tying themselves in knots.

• Endoparasites - feed by borrowing into the mouth, gills, or anus of a host fish and consuming their prey from the inside out.

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Superclass Gnathostomata• Jaws• Paired appendages

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Fig. 48.13

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Class Chondrichthyes

• Cartilaginous skeleton• Notochord present• No opercula. Must

swim constantly to allow oxygenated water to move across gills.

• No swim bladder. They are unable to regulate their buoyancy levels.

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Superorder: Selachimorpha(Sharks)

Dogfish Shark

Superorder: Selachimorpha

• Respire with the use of 5 to 7 exposed gill slits.

• Skin covered with dermal denticles - tooth-like structures that protect the skin and cause it to feel like sandpaper when rubbed against the grain.

• Denticles also produce small vortices that reduce hydrodynamic drag and increase swimming efficiency

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Superorder: Selachimorpha

• The largest of all fish is the whale shark. It is a filter feeder.

• Most sharks are simple carnivores.

• Teeth are anchored into flesh rather than bone and they rip out and are replaced very rapidly.

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Superorder: Selachimorpha• Although most fish are

exothermic, the short-fin mako shark and the great white shark are slightly endothermic.

• Most sharks are ovoviviparous. They carry their eggs internally until the young hatch and are born alive and fully functional.

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Superorder: Selachimorpha

• Sharks have electroreceptor organs called the Ampullae of Lorenzini that detect the electromagnetic fields that all living things produce. This assists sharks in hunting and in navigation.

• Sharks also have a very keen sense of smell and can detect 1:1,000,000 blood in water.

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Superorder: Batoidea(Rays & Skates)

Stingray

Superorder: Batoidea• Possess 5 gill slits

that are located underneath the pectoral fins rather than on the side of the head as in sharks.

• Body is flattened and wide instead of streamlined like sharks.

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Superorder: Batoidea• Wide distribution of group

members. Tropical to cold-water species exist.

• Most are benthic (live on the sea floor) and respire by moving water in through their spiracles towards their gills.

• Manta ray is an example of a rare pelagic batoidean.

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Superorder: Batoidea• Skates and rays are very similar. However,

skates tend to have a more shovel-shaped head than rays and they lack spines in their tails.

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Class Placodermi• Among the first jawed

fish along with the ancestors of Class Chondrichthyes

• Went extinct along with the Ostracoderms

• Head and thorax were covered by bony plates

• 320 mya fossil shows earliest example of viviparous birth

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Class Osteichthyes

• Boney fish. Actually called endochondral bone because it is formed by the ossification of cartilage.

• Comprise the most various and largest class of vertebrates on Earth today.

• Includes the vast majority of all fish.

Class Osteichthyes• Swim bladder present.

Allows a fish to adjust its buoyancy and thus its position in the water column.

• Operculum present. Allows fish to pump water across the gills without having to physically move through the water.

• Lateral line – senses vibrations in the water

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Subclass Actinopterygii

• Comprised of most members of class Osteichthyes.

• Fins supported by bony rays.

• All members have homocercal tails.

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Subclass Sarcopterygii

• Lobed fins joined to the body at a single bone.

• Two dorsal fins with separate bases and diphycercal caudal fins

• There are only 8 living species in this subclass. These include lungfish and coelacanths.

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Subclass Sarcopterygii

• Lungfish are able to utilize a primitive lung to breath air when their ponds dry out or the water becomes anoxic.

• Lungfish are known to use their fleshy pectoral fins like legs and crawl to new ponds when their previous ponds dry out.

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Subclass Sarcopterygii• The subclass split into two main groups long ago with

the coelacanths staying in the ocean and the lungfish & tetrapodomorphs moving to freshwater environments.

• Tetrapodomorphs further evolved into land vertebrates.

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Fish Scales

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Countercurrent Exchange

Buoyancy• Sharks must constantly

swim to keep from sinking. They use dynamic lift to maintain a constant level in the water column.

• Oils in sharks’ livers and the ability of some sharks to swallow air allow then to obtain some level of buoyancy.

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Buoyancy• Members of class

Osteichthyes possess a swim bladder that is able to fill with air and alter the buoyancy of the fish.

• The bladder fills by gas exchange with blood vessels lining the sac. As oxygen diffuses in the sac, the fish becomes more buoyant and rises. The process works the same in reverse.

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Osmoregulation in Fish

1% Salt

HYPER, HYPO, ISOTONIC?

Freshwater Fish (Hypotonic)

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1% Salt

0% Salt Water

Salt

UrineAbsorb Salt

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Marine Fish (Hypertonic)

1% Salt

3.5% Salt Water

Salt

UrineSecrete Salt

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Reproduction

• Oviparous – Lay eggs outside the body so they may

develop and hatch.

• Ovoviviparous– Egg remains in mother until offspring hatch– The offspring are born alive

• Viviparous– Embryo receives nourishment from mother– The offspring are born alive

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Courtship Behavior