Answer:
A major morphological criterion on which traditional classification of animals was based is body symmetry.
Step-by-step explanation:
Traditional classification of animals often relied on observable physical characteristics, such as body symmetry, to categorize and group organisms. Body symmetry refers to the arrangement of an organism's body parts around a central axis. There are two main types of body symmetry found in animals: radial symmetry and bilateral symmetry.
Radial symmetry: Organisms with radial symmetry have body parts arranged symmetrically around a central point, like spokes on a wheel. Examples of animals with radial symmetry include sea anemones, jellyfish, and starfish.
Bilateral symmetry: Organisms with bilateral symmetry have body parts arranged symmetrically along a central axis, creating distinct left and right sides that are mirror images of each other. Most animals, including humans, insects, and mammals, exhibit bilateral symmetry.
This morphological criterion was used in traditional classification systems to distinguish between different groups of animals and understand their evolutionary relationships. However, modern classification systems also incorporate other factors, such as molecular and genetic data, to create a more comprehensive understanding of the relationships between organisms.