On a cold afternoon at the beginning of February I visited Swansea Bay in South Wales. The tide was out. Tubes made from sand-grains clustered together forming massive reefs on boulders at the low tide mark. The tubes are formed by colonies of marine worms known as honeycomb worms (Sabellaria alveolata). The image below is a close-up of the same type of tubes taken at Lyme Regis in Dorset.