Chordates {chordate}| (Chordata) are deuterostomes and have bilateral symmetry.
types
Amphioxus is a living chordate, has no jaw, is flat, and is small. Pikaia was an ancient chordate [Bone, 1979].
evolution
Hemichordata ancestors and Echinodermata and Pterobranchia ancestors split. Chordata ancestors and Hemichordata ancestors split. Chordates developed from prechordate larval forms.
notochord
Early chordates had one firm cartilage segmented rod down back along body long axis, allowing increased swimming efficiency by providing places for muscle attachment. Adult notochords allowed reproductive-method changes.
external respiration
Early chordates had paired pharyngeal gill slits. Side openings allowed greater water flow into mouth, over gills, and out body. Blood oxygen uptake and carbon-dioxide removal became more efficient with gills.
filter feeding
Skin calcification made dermal bone that allowed structures for catching small organisms in water flowing into mouth. Filter feeding gathered more food and calcium.
nervous system
Dorsal hollow nerve lay along back under notochord, from periphery to head, and had sense and motor pathways. Cerebrospinal fluid formed in middle.
brain
Head ganglion unified control over all body segments and other ganglia, coordinating sense input and motor output. Brain allowed better swimming, burrowing, and defense and more coordinated behavior. Eye, pineal gland, hypothalamus, and hindbrain began in chordates. Chordates had serotonin neurons, which later evolved to brainstem.
senses
Sense cells detected motions and stationary patterns.
Biological Sciences>Zoology>Kinds>Chordate
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Date Modified: 2022.0224