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What four major animal divisions did Georges Cuvier propose?

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Marble bust of Aristotle with a beard and draped robe, showing detailed facial features and wavy hair, set against a dark background. — Philosophy of biology Detail of a Roman copy (2nd century bce) of a Greek alabaster portrait bust of Aristotle, c. 325 bce; in the collection of the Roman National Museum.

In his work Le Règne animal distribué d’après son organisation, the French zoologist Georges Cuvier rejected the 18th-century concept of a single, linear chain of life. Instead, he proposed that animals should be classified into four distinct groups, or "branches," based on their specific anatomical organization.12

The four major animal divisions proposed by Cuvier were:

Vertebrates: Animals possessing a backbone and internal skeleton.12
Mollusks: Animals characterized by a soft body, often protected by a shell.12
Articulates: Animals with segmented bodies, such as insects and crustaceans.12
Radiates: Animals exhibiting radial symmetry, such as starfish and jellyfish.12

Cuvier argued that these four types were completely distinct and represented fundamental differences in anatomical structure, rather than variations along a continuous scale. While modern biological classification has evolved significantly since his time, Cuvier’s approach was a significant advancement that laid the groundwork for future systematic zoology.12