Christmas tree worms (Barry Peters / CC BY)
The sedentary Christmas tree worm has a segmented body that is typically anchored in a tubular burrow. Only two modified prostomial palps are visible from the outside. These small spiral structures (3.8 centimeters or 1.5 inches in span) are brightly colored and resemble Christmas trees. The worm uses the spirals for feeding and respiration. When disturbed, they are rapidly retracted into the burrow.