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How do bony fishes differ from cartilaginous fishes?
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Chordate
X-ray fish (Pristella maxillaris), is an example of a chordate with a visible backbone.
Bony fishes (Osteichthyes) and cartilaginous fishes (Chondrichthyes) differ significantly in their anatomy and physiology:
- Skeleton: As the name implies, bony fishes possess a skeleton composed at least partly of true bone, whereas cartilaginous fishes (such as sharks, skates, and rays) have skeletons made of cartilage.4
- Buoyancy: Most bony fishes have a swim bladder, a gas-filled organ that helps them maintain buoyancy. This organ is absent in all cartilaginous fishes.12
- Gills: Bony fishes typically feature a bony, movable gill cover called an operculum that protects the gill chamber. In contrast, cartilaginous fishes have exposed gill slits or flaps of skin.32
- Scales: Bony fishes often have bony, platelike scales (such as cycloid or ctenoid types). Cartilaginous fishes are characterized by spiny, toothlike placoid scales, also known as denticles.45
- Reproduction: While bony fishes often utilize external fertilization, cartilaginous fishes exclusively employ internal fertilization.46