Make your own free website on
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.
Superclass Gnathostomata
"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.
Class Chondricthyes
"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).
"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.)
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.