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  • Fish are vertebrates with gills and paired fins. Gills are used to breath underwater, allowing fish to take in dissolved oxygen from water, and release carbon dioxide. Fins help keep fish stable by redirecting water around the fish as it swims, they also help fish to maneuver in water. 

    Modern fishes include an estimated 31,000 species. Fishes were the earliest vertebrates, with jawless species being the earliest and jawed species evolving later. They are active feeders, rather than sessile, suspension feeders. Jawless fishes—the hagfishes and lampreys—have a distinct cranium and complex sense organs including eyes, distinguishing them from the invertebrate chordates.


    Figure 1. Pacific hagfish are scavengers that live on the ocean floor. (credit: Linda Snook, NOAA/CBNMS)

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