Phylum Chordata

Characteristics At some point in life: – Nerve cord. – Notochord. – Gill slits. – Tail. Bilateral symmetry. Ventral heart.

Classification Includes two subphyla of invertebrates: – Urochordata (tunicates and sea squirts). – Cephalochordata (lancelets). Includes one subphyla of vertebrates. – Vertebrata.

Characteristics of the Vertebrates Notochord develops into vertebral column. Two pairs of appendages. Anterior skull. Large brain. Large coelom for internal organs. Closed circulatory system. Gas exchange via gills or lungs. Skin acts as an outer covering.

Subphylum Vertebrata Seven classes.

Superclass Agnatha e.g., Lampreys. Cartilaginous skeleton and contains notochord. Lack jaws, paired fins and appendages. Live as external parasites on fish. Gas exchange via gill slits.

Class Chondrichthyes e.g., Sharks, rays and skates. Cartilaginous endoskeleton Ectothermic. Thick fins. Skin covered in denticles. Gill slits. Two-chambered heart.

Class Chondrichthyes

Class Osteichthyes e.g., Bass, pike and salmon. Boney endoskeleton. Ectothermic. Thin, membranous fins. Thin, smooth scales cover body. Gills covered by operculum. Swim bladders (air-filled for buoyancy). Two-chambered heart.

Class Amphibia e.g., Frogs, toads & salamanders. Aquatic larval stage with gills. Terrestrial adults are tetrapods. Ectothermic. Respiration via lungs and/or skin. Three-chambered heart.

Class Amphibia

Class Reptilia e.g., Snakes, turtles, lizards, crocodiles. Mostly terrestrial tetrapods with dry scaly skin. Ectothermic. Respiration via lungs. Amniotic eggs with soft shells. Three-chambered heart.

Class Aves e.g., Birds. Tetrapods covered in feathers. Forelimbs modified as wings. Most capable of flight. Hollow bones. Lungs connected to air sacs. Endothermic. Amniotic eggs with hard shells. Four-chambered heart.

Class Aves

Class Mammalia e.g., Humans, pigs and deer. Tetrapods covered in hair. Mammary glands for nursing young. Endothermic. Specialized teeth. Four-chambered heart.

Class Mammalia Monotremes: – Lay eggs. – Platypus and spiny anteater.

Class Mammalia Marsupials: – Pouched mammals. – Kangaroo, opossum & koala.

Class Mammalia Placentals: – Offspring develop in uterus. – More developed than marsupials at birth. – Most common form of mammals.