Cirratulus cirratus is a species of marine polycheate worm in the family Cirratulidae. It occurs in the littoral and sub-littoral zones of the Atlantic Ocean. Polychaetes, or marine bristle worms, have elongated bodies divided into many segments. Each segment may bear setae (bristles) and parapodia (paddle-like appendages). Some species live freely, either swimming, crawling or burrowing, and these are known as "errant". Others live permanently in tubes, either calcareous or parchment-like, and these are known as "sedentary".