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How are vertebrates grouped by their body structures?
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Chordate
X-ray fish (Pristella maxillaris), is an example of a chordate with a visible backbone.
Vertebrates are classified into four major groups based on their morphology:
- Cyclostomes: These jawless fishes, such as lampreys and hagfishes, lack lateral fins and jaws. They represent the most primitive group, retaining a notochord throughout their lives.12
- Chondrichthyes: This group consists of cartilaginous fishes, including sharks, rays, and chimaeras. They possess a vertebral column composed of cartilaginous, partly calcified centra.12
- Teleostomes: Also known as bony fishes, this group includes ray-finned and lobe-finned fishes. Their vertebrae are often completely ossified, developing outside the notochordal sheath.12
- Tetrapods: This group includes all limbed vertebrates, specifically amphibians, reptiles, birds, and mammals. They are characterized by specialized body plans featuring limbs and distinct regional differentiation of the vertebral column, such as the development of cervical, thoracic, and lumbar regions.13
These structural variations are governed by regulatory genes, such as Hox genes, which determine the spatial organization of body parts during embryonic development.4