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Copepod. Image credit: NASA/JPL
Any of the roughly 7,500 species of marine or freshwater crustacea of the subclass Copepoda. Copepods are possibly the most numerous type of animal in the world and are a major component of the ocean food chain. Some live as parasites, especially on fish. Their segmented, cylindrical bodies have a single median eye and no carapace. Copepods are typically 0.5–2 mm (0.02–0.08 in.) in length, although some parasitic forms may be more than 30.5 cm (1 ft) long.

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