Baleen plates arise in the fetus as thickenings of skin on the upper jaw. At birth, baleen is soft and short, but it soon stiffens. The frayed edge of each plate intertwines to form a mat which functions as a strainer during filter feeding. Gray whales have about 130 to 180 baleen plates on each side. The right whale family, notably the bowhead whales, have the longest baleen.
Baleen plates range in color from black to yellow or white, depending on the species.
Baleen whales retain tooth buds during the embryonic stage. These tooth buds disappear before birth. Baleen whales have a smooth skin surface with no oil glands or pores. Many species have several hairs located on the snout, jaws, and chin. Samples of skin and blubber have been collected by shooting a hollow dart into a whale's body.