Higher Chordates:Fishes & Amphibians

Chapter 34

Phylum Chordata

Recall:

• Subphylum Urochordata– Tunicates

• Subphylum Cephalochordata– Lancelets

• Class Myxini– Hagfish– Least derived craniate lineage still surviving

• Chordates with a head

Subphyla Vertebrata

• Endoskeleton– Vertebrae: bone or

cartilage

• Closed circulatory system– Single well developed

heart

• Skull with a brain– Anterior to the spinal cord

• Extinct vertebrate: – Conodont

Class Agnatha• Jawless fish

– Ostracoderms• extinct

– Cyclostomes• Lampreys, hagfish

• Lack paired fins, scales

• First organisms with a backbone

• Appeared 500 mya

Class Acanthodia

• Spiny fish • Developed jaws

with bony edges– Gnathostomes

• Internal skeletons of cartilage

• Extinct • Appeared 430 mya

Class Placodermi

• Fish with massive heads

• Extinct• Appeared 410 mya

Class Chondricthyes• Cartilage fish (bone in teeth & scales)• Sharks, skates, rays, ratfish & chimeras• Appeared 400 mya

Chondricthyes characteristics

• Premier Predators– Streamlined body (power, not grace)– Oil bladder (buoyancy)– Acute vision (but colorblind)– Detect electric fields

Chondricthyes characteristics• Reproduction

(variety)– Oviparous

• lay eggs externally

– Ovoviviparous• keep eggs in uterus

until hatching

– Viviparous• Placenta – live birth

Class Osteichthyes• Ossification of the skeleton (Bone)• Draw H2O across gills

– Operculum bony covering• Swim bladder (buoyancy)• Mostly oviparous• Appeared 400 mya• 95% of today’s fishes

Subclass Actinopterygii

• Ray finned fish– Bony rays in fins

for maneuvering, defense, and other functions

Subclass Sarcopterygii

• Lobe finned fish– Rod-shaped bones in fins surrounded with

thickened layer of muscle– Swim or “walk” across substrate

• Actinista (coelacanth)• Dipnoi (lungfish)

Evolution of tetrapods

One of the most significant events in vertebrate history was when the fins of some lobe-finned organism evolved into the limbs and feet of tetrapods

Class Amphibia

• “Two lives”– aquatic larva develops into a terrestrial adult

• Gas exchange– Lungs and moist skin

• All amphibians must lay eggs in water

Order Urodela

• Salamanders– tails

Order Anura

• Frogs and toads– No tail

Order Apoda

• Caecilians– Legless– Wormlike– Burrowing

Amphibian Metamorphosis