By what feature are marine animals distinguished?

Marine animals are primarily distinguished by the presence of jaws, which is a significant evolutionary feature that sets them apart from many other aquatic organisms. Jaws allow these animals to have a more diverse diet, enabling them to catch, chew, and consume different types of prey, which has implications for their survival, reproduction, and ecological interactions.

While color, fins, and skin texture do play roles in the identification and classification of marine animals, they can be variable and influenced by environmental factors, adaptations, and mimicry among various species. Jaws, on the other hand, represent a definitive anatomical characteristic that has had a profound impact on the evolution and functional capabilities of marine life. The presence of jaws marks a critical point in the evolutionary lineage, especially when considering the distinction between certain sub-groups, such as jawed vertebrates versus those without jaws, like some primitive fish and invertebrates.