Animal Phylogeny and Chordate Classification

Bilateria

Animals with bilateral symmetry and three tissue layers.

Deuterostomes

Animals where the blastopore becomes the anus.

Radial symmetry

Body plan symmetrical around a central axis.

Bilateral symmetry

Body plan with left and right mirror images.

Tube-within-a-tube body design

Body structure with an inner and outer tube.

Notochord

Flexible rod providing support in chordates.

Dorsal nerve cord

Hollow nerve cord forming the spinal cord.

Pharyngeal slits

Structures for filter feeding or respiration.

Post-anal tail

Tail extending beyond the anus in embryos.

Cephalochordates

Invertebrate chordates known as lancelets.

Urochordates

Tunicates with a polysaccharide body covering.

Vertebrates

Chordates with a backbone or vertebral column.

Synapomorphies

Shared derived traits defining a clade.

Cyclostomes

Jawless fishes including hagfishes and lampreys.

Gnathostomes

Jawed vertebrates including sharks and tetrapods.

Chondrichthyes

Cartilaginous fishes like sharks and rays.

Osteichthyes

Bony fishes, including ray-finned and lobe-finned.

Actinopterygii

Ray-finned fishes with thin, bony fins.

Sarcopterygii

Lobe-finned fishes with fleshy, lobed fins.

Amniota

Group including reptiles, birds, and mammals.

Echinodermata

Marine animals with radial symmetry, like starfish.

Hemichordata

Acorn worms, outgroup to chordates.

Cranium

Bony structure protecting the brain.

Gill arches

Structures that evolved into jaws in gnathostomes.

Tetrapoda

Four-limbed vertebrates including amphibians and mammals.