Polydora ciliata is a species of annelid worm in the family Spionidae, commonly known as a bristleworm.

The multi-segmented body is broadest fairly near the front and then tapers gradually to the pygidium (terminal segment) which bears a funnel.

As a burrowing species, it tunnels into limestone; chalk and clay, calcareous algae, the holdfasts of seaweeds, wood, muddy sediment and mollusc shells, including those of oysters, mussels and periwinkles.

[4] The burrow of P. ciliata is U-shaped, and the presence of these worms can be recognised by the sets of small, double perforations they make.

The tube is lined with mucus and fine grains of sediment and extends slightly above the surrounding material.