Chordates, Fishes & Amphibians

Chordates● Chordate- members of the phylum Chordata

● Must have 4 characteristics at some stage in life● Dorsal hollow nerve cord● Notochord- long supporting rod that runs through body just

below nerve cord● Pharyngeal pouches- paired structures in throat region● Tail that extends beyond the anus

● Most chordates are vertebrates● They have vertebrae- individual segments that make up the

backbone & encloses the spinal cord

Fishes● Aquatic vertebrates that (for the most part)have:● Paired fins- for movement● Scales- for protection● Gills- for gas exchange

● Feeding● Every mode of feeding found in the fishes● Some may vary feeding depending upon what is available● Have specialized fingerlike pouches called pyloric ceca that

secrete digestive enzymes & absorb nutrients

● Respiration● Most use gills that are made up

of filaments

● Filaments provide large surface area for exchange of oxygen & carbon dioxide

● Bring water into mouth and move it over the gill filaments and out the gill slits

● Circulation● Closed circulatory system

● Blood is pumped from heart to the gills (where it gets oxygen) and then to the rest of the body and back to the heart

● Most fishes have a 4-part heart, with TWO chambers● Atrium- blood enters and flows to the ventricle● Ventricle- pumps blood into bulbus arteriosis

● 2 chambers: atrium & ventricle

● Response● Well-developed ● Brain has several parts

● Olfactory lobe- smell● Cerebrum- voluntary activities● Optic lobe- vision● Cerebellum- body movements● Medulla oblongata- functioning of internal organs

● Lateral line system- allows fishes to detect gentle currents & vibrations

● Movement● Alternately contract paired muscles on either side of

backbone● This creates backward force on the surrounding water & when

fins move, it propels the fish forward

● Many bone fishes have a swim bladder that adjusts their buoyancy b/c their tissue is more dense than the water

● Reproduction● Eggs are fertilized either internal or external, depending on

the species● Oviparous- eggs hatch outside the mother’s body● Ovoviparous- eggs remain in the mother after fertilization &

are “born alive” using yolk for nutrients while developing● Viviparous- embryos remain in mothers body and get

nutrients from mother

Excretion● Rid themselves of nitrogenous wastes in form of ammonia

● Some wastes diffuse through gills

● Kidneys remove wastes from the blood

Groups of Fishes● Jawless fishes (Class Agnatha)- have no true teeth or jaws

● Lampreys & hagfishes

● Cartilagenous fishes (Class Chondrichthyes)- skeleton made of cartilage- no bones!● Sharks, rays● Have many rows of teeth● Have toothlike scales covering skin to make it rough

● Bony fishes (Class Osteichthyes)- skeleton made of bone● Ray-finned fishes have slender bony spines connected to fins● Flounder, bass, catfish, angelfish

Amphibians● Amphibian means double life- meaning live both in water

and on land● Lives in water as a larva● Lives on land as an adult● Breathes with lungs as an adult● Has moist skin that contains mucus glands● Lacks scales and claws

● Feeding● Tadpoles are filter feeders or herbivores● Adults are carnivorous● At end of digestive tract is large muscular cavity called cloaca

which is where digestive wastes, urine, eggs/sperm leave the body

● Respiration● Gas exchange occurs through skin and gills in the larval stage● In adults, the gills are replaced by lungs

● Circulation● Double-loop

● First loop carries oxygen-poor blood from heart to the lungs and skin & takes oxygen-rich blood from the lungs and skin back to the heart

● Second loop transports oxygen-rich blood from heart to rest of the body and oxygen-poor blood from body back to the heart.

Amphibian heart has 3 chambers

● Excretion● Kidneys filter wastes from the blood● Urine travels through waste to ureters & out the cloaca

● Reproduction● Eggs are laid in water, so can keep moist● In frogs, the male will squeeze a female & she will release

eggs which he then fertilizes- Externally

● Movement● Larvae move like fishes● Most adults have 4 limbs use legs to move

● Response● Well-developed nervous system, similar to the fish● Have a nictitating membrane covering the eye to keep it

moist on land and protect it under water● Hear through a tympanic membrane located on each side of

the head

Groups of Amphibians● Salamanders (order Urodela)● Have long tails● Carnivores at all stages● Include salamanders & newts

● Frogs & Toads (order Anura)● Jump● Frogs have long legs, toad legs are shorter● Frogs are generally aquatic, toads are terrestrial● Both lack tails

● Caecilians (order Apoda)● Legless animals● Many have scales