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Related to cetaceous: Sirenians
Any of various marine mammals of the order Cetacea, including the whales, dolphins, and porpoises, having the general shape of a fish with forelimbs modified to form flippers, a tail with horizontal flukes, and one or two blowholes for breathing.
[From New Latin Cētācea, order name, from Latin cētus, whale; see Cetus.]
ce·ta′cean, ce·ta′ceous (-shəs) adj.