Polychaetes exist in both free-living and tube-dwelling forms, and may vary in size from only a few millimeters long to lengths as great as 10 feet. The segmented worms bear pairs of fleshy appendages called parapodia on most of their segments and the outgrowths are generally equipped with numerous setae, or bristles. Most of the organisms, which often exhibit bright colors, are also outfitted with palps and tentacles on their heads. However, the heads of some sedentary polychaetes may be indistinct, and those tube-dwelling varieties with distinct heads often lack head appendages.