Subfamily Spirorbinae

The subfamily Spirorbinae is a subset of the polychaete worms (marine worms).  Spirorbin worms form a tiny, calcareous spiral shell which houses the animal.  The worm can fully retract into the shell, or may extend its radioles (feathery appendages) to feed.  One paddle-shaped radiole is used to close up the mouth of the shell when the worm is retracted. 

Anatomy of Spirorbin worms

Radioles- feathery appendages which can extend from the mouth of the shell to collect food
Operculum- a modified radiole used to cover the mouth of the shell