Pomatoceros triqueter

Pomatoceros triqueter is a species of tube-building annelid worm in the class Polychaeta. It is common on the north eastern coasts of the Atlantic Ocean and in the Mediterranean Sea.
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".
Distribution
This species is found in the Arctic, eastern North Atlantic, the Mediterranean, Adriatic, Black and Red Sea, the English Channel, the North Sea, Skagerrak, Kattegat the Little and Great Belts and Øresund north east to the Bay of Kiel.
Description
Pomatoceros triqueter secretes a white calcareous tube about three millimetres wide and up to twenty five millimetres...