Final answer:
Bony fish have a skeleton made of ossified bone, providing them with a sturdy internal structure, except for a few like sturgeons and paddlefish with cartilaginous skeletons. They make up the largest class of vertebrates with around 30,000 species.
Step-by-step explanation:
Bony fish, belonging to the clade Osteichthyes, are characterized by having a skeleton composed of ossified bone with specialized bone cells known as osteocytes. These cells produce and maintain a calcium phosphate matrix, giving the bony fish a sturdy internal structure. However, a few exceptions exist, such as sturgeons and paddlefish, which have retained primarily cartilaginous skeletons.
The skeleton of bony fish offers several evolutionary advantages, including support for larger body sizes and the attachment of muscles that aid in movement. Additionally, bony fish have developed other adaptations, such as scales for protection, glands for mucus secretion to aid in swimming and osmoregulation, and sensory systems like the lateral line for detecting vibrations in the water. Their evolutionary journey has led to a vast diversity in the present day, with around 30,000 species, making them the largest class of vertebrates in existence.