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Bio Notes 7 - Feb 17th

Superclass Agnatha

"Jawless Vertebrates"
Probably arose in the late precambrain & early cambrian.
-Early Agnathans small, less than 50 cm in length.
-They were jawlessw/ oval or slit slike mouths; MOST lacked paired fins & were bottom dwellers (benthic)
-Some were active & had paired fins
-Ostracoderms were the earliest vertebrates & declined during Devonian period (Age of Fishes)
-Lampreys & Hagfish are the only extant agnathans
-Extant forms include about 60 species of Lampreys & hag fish which lack paired fins & external armor.
-Lampreys are Ectoparasitic (eat living host) & use rasping tongue to penetrate skin & feed on prey's (fish) blood.
-Spend larval development in fresh H2O streams & migrate to sea or lakes as they mature.
-Hagfish superficially resemble lampreys
-They (Hagfish) are scavengers (dead of dying things) NO rasping mouthparts.
-Exclusively marine.
-Some species feed on sick or dead fish & others feed on marine worms.
-Lack a larval stage.
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Superclass Gnathostomata
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"Jawed Vertebrates"
-Agnathans gradually replaced by verts w/ jaws.
-Early Gnathostomes included class Chondricthyes (cartilaginous), Osteichthyes (bony fish). & a now extinct group of armored fish called Placoderms. Class Placodermi had paired fins & hinged jaws.
-Hinged jaws evolved as modifications of gill arches (skeletal rods) which previously supported the anterior pharyngeal (gill) slits.
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Class Chondricthyes
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"Cartilaginous Fishes"

About 750 extant species of cartilaginous fishes
(Sharks, skates, rays, Chimera-Ratfish).
Ratfish may be evolutionary link b/w sharks & bony fish.
-Group has flexible skeletons composed of cartilage
-Well developed jaws
-Paired fins
-Ancestors had bony skeletons
-Cartilaginous skeleton is a derived characteristic, (ancestors were bony then evolved a cartilaginous skeleton), evolving secondarily
-Parts of the skeleton are strengthend by calcified granule.
-Continual swimming produces H2O flow through mouth & over gills for gas exchange.
-Some sharks rest on sea floor & in caves; use jaw & pharyngeal muscles to pump H2O over gills while resting.
-Some buoyancy provided by large amounts of oil stored in liver (no swim bladder). Most continuallly swim to remain in H2O column.
-Most shark are carnivorous. (literally meat eating - not eating plankton)
-Largest sharks & rays are suspension feeders (whale sharks, basking sharks).
-Teeth evolved as modified scales (Placoid scales, Dentricles (little teeth))
-Digestive tract proportionately shorter than in other vertebrates.
-Spiral Valve increases surface area & slows movement in intestine (to compensate for small digestive tract).
-Sharks possess sharp vision (can't distinguish color) & Olfactory senses.
-Electric sensory regions (Ampullae of Lorenzini) detect muscle contractions /*the electrical responses produces by that */ of prey located on the head.
-Lateral line system along the flanks.
-Composed of microscopic organs sesitive to H2O pressure changes & detects vibrations.
-Sharks reproduce sexually w/ internal fertilization
-Pair of claspers on pelvic fins of males transfers sperm into females reproductive tract.
-Oviparous (Egg laying) Ovoviparous (eggs hatch in female tract & come out alive) (Viviparous (true live barrer))
Some species are oviparous, ovoviviparous, & a few are viviparous.
-Cloaca(Sewer in Latin-everything goes there) (Common chamber for reproduction, digestive, or excremtory system) is present).
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Osteichthyes
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"Bonyfishes" 3 classes
30,000+ Extant species largest group of vertebrates.
-Abundant in marine & fresh H20
-Skeleton bony, reinforced w/ calcium phosphate
-Skin covered w/ flatened, bony scales
-skin glands produce mucus that reduces drag when swimming
-Lateral line system present.
-Gas exchange occurs by drawing H2O over 4 or 5 pairs of gills located in chambers covered by operculum (gill cover)
-Swim bladder located dorsal to digestive tract, provides buoyancy. Transfer of gases b/w blood & swim bladder.(when want to sink - they decrease the inflation on the flatter & vice versa)
-Varies bladder inflation & adjusts the density of the fish.
-MOst bonyfish are oviparous(egg layers w/external fertilization) w/ external fertilization
-SOME are ovoviparous (Egg layers inside) or viviparous (truly live barrers) w/ internal fertilization.
-Rivulus marmoratus rare FL killifish is the only self- fert Hermaphroditic vertebrate. Has an "Ovotestis"
-Sharks arose in the sea, bony fishes probably originated in fresh H2O.
-Swim bladder was modified from lungs of Ancestral Fishes which supplemented the gills for gas exchange in stagnant waters. (Lung fish get air by gulping at the surface - needed due to lack of O in stagnant H2O.)
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3 Extant class of
"Bony Fishes" (Osteichthyes)
1) Class Actinopterygii

"Ray-finned Fishes"

-most familiar fish

-fins suported mainly by flexible rays.


2) Class Actinistia
"Lobe-finned fishes"
-Fins fleshy, muscular & supported by extension of bony skeleton.