Baleen whales have two eyes, a mouth, baleen, a rostrum (the section above their mouth), two ears, dorsal fins or ridges, two flippers, a tail composed of two segments called "flukes," two blowholes for breathing, and throat grooves, which may expand or stretch while they take on water during feeding. They also have the umbilicus as well as a urogenital slit. However, external anatomical differences exist among the various types of baleen whales. These include lack of a dorsal fin, variance in overall size, lack of throat grooves and rough patches of skin on the top of the head called callosities.
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