A shark is a vertebrate, not an invertebrate. This classification stems from fundamental biological differences in their internal structures.
Defining Invertebrates
Invertebrates are animals that do not possess a backbone or spinal column. They represent the vast majority of animal species on Earth, making up approximately 97% of all animal life. These animals exhibit incredible diversity in their body plans and support systems.
Many invertebrates, such as insects and crustaceans, have an external skeleton called an exoskeleton for structural support and protection. Other examples include soft-bodied organisms like jellyfish, which use a hydrostatic skeleton, or mollusks like snails, often protected by shells. Common invertebrates found across various habitats include worms, spiders, and starfish.
Defining Vertebrates
Vertebrates are animals characterized by the presence of a vertebral column, commonly known as a backbone or spine. This internal structure protects the spinal cord and provides central support for the body. The vertebral column is part of a larger internal skeleton, or endoskeleton, which can be made of bone or cartilage.
Vertebrates possess a well-developed nervous system, including a brain enclosed within a skull. They also feature a distinct head region and often have specialized sensory organs such as eyes and ears. This group encompasses a wide range of animals, including fish, amphibians, reptiles, birds, and mammals.
Sharks: A Vertebrate Classification
Sharks are classified as vertebrates. The primary reason for this classification is their vertebral column, which encases the spinal cord.
While many vertebrates have skeletons made of bone, sharks and their relatives, such as rays and skates, have skeletons composed primarily of cartilage. This cartilaginous skeleton, which is lighter and more flexible than bone, does not prevent them from being vertebrates. The presence of a backbone, regardless of its material composition, is the determining factor for vertebrate classification.
Sharks also display other features typical of vertebrates, including a well-developed brain protected by a skull, a complex nervous system, and a closed circulatory system. Confusion about sharks’ classification often arises because their cartilaginous skeletons differ from the bony skeletons found in most other fish. However, their anatomical features, such as the distinct vertebral column and skull, align them with vertebrates. Sharks are a part of the class Chondrichthyes, which includes all cartilaginous fish.