Transcript Lecture 24 Jawless Fish - NGHS

Jawless Fish
Phylum: Chordata
Sub-Phylum: Vertebrata
Class: Agnatha
Fish
The 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
Hagfishes
• 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
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
Lampreys
http://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."
Jawless Fishes – modern diversity
Hagfish
Lamprey
Larvae of a jawless fish
Skeletal elements of a jawless fish
Jawless Fishes – modern diversity
lampreys
Jawless Fishes – ancient diversity
EXTINCT JAWLESS FISH
Paired
Fin
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
Interpret This Graph