Jawless FishPhylum: Chordata

Sub-Phylum: VertebrataClass: Agnatha

FishThe Water Dwellers

Most fish are cold blooded vertebrates that live in water. Scientists believe that fish were the only vertebrates on Earth for about 150 million years.

Scientists classify fish living today into three classes.

Subphylum Vertebrata

Fishes

Jawless Fishes•Do not have a lateral line system•45 species of lampreys (fresh water) and hagfish (oceans)•Cyclostomes “round mouths” ; have neither plates nor scales•Notochord, eel-like shape, a cartilaginous skeleton, and unpaired fins

Jawless fish: Hagfish

• Hagfish are of the order, Myxiniform. They are related to the slimefish. They have the peculiar habit of tying themselves into knots in order to shed their slime coat and make a new one.

• 20 known species• Deep, cold waters• 2.6 ft.• Skin is used for leather goods

Hagfishes

Hagfish• feed on polychaete worms, shrimp, and dead or dying fish • attach to fish, form a knot in the tail and pass it forward to rip off

flesh.  Image © BIODIDAC. • usually enter coelomic cavity and feed on soft parts• many mucous glands present for anti-predator defense

• Bottom dwellers in cold marine waters

• Feed by sawing the fish with its toothed tongue from the inside out

• Extremely flexible to avoid capture or to clean the slime off after self-defense secretions

• When not feeding they remain hidden in burrows on the ocean floor

Jawless fish: Lamprey

Lampreyshttp://itech.pjc.edu/jwooters/zoology/virtual_review/lamprey.htm

• Lampreys are of the order, Petromyzontiform. They are suckers and attach themselves to fish in order to parasitize off them.

• Found in Freshwater• 30 species

- free living or parasitic; adapted for sucking blood and body fluids of other fish - highly developed sense of smell: nasal pore leads to olfactory sacs that connect with olfactory lobes - Feeding: attach by suction, tear a hole with toothy tongue, secrete chemical to prevent clotting - do not have a stomach: mouth, esophagus, a straight intestine, and associated glands

Sea Lamprey Life Cycle

• Life cycle of sea lamprey– Adult parasitic, feeding

stage– Adults swim into small

freshwater streams to breed

– Larvae live in sediment as filter feeders up to seven years

– Metamorphosis, migration to lake or sea to become parasitic adults

Lamprey Anatomy

FINS

LIVING JAWLESS, e.g. LAMPREY: ONLY ALONG BODY

D-eel-icious, if you appreciate an earthiness

• So what does lamprey taste like? "I would have to say it tastes like lamprey," says Chef Bob Bennett, "because it does not have a flavor that you can associate with anything else."

Hagfish

Lamprey

Jawless Fishes – modern diversity

Larvae of a jawless fish

Skeletal elements of a jawless fish

lampreys

Jawless Fishes – modern diversity

Jawless Fishes – ancient diversity

EXTINCT JAWLESS FISH

PairedFin

EVOLUTION

• Earliest fish – Ostracoderms• fossils date to the Ordovician

Period – 425-450 Million years ago

• slow, bottom-dwelling w/thick bony plates and scales, poorly developed fins and no jaws

• believed to be first animal w/a backbone

• became extinct 250 million years ago

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