Sea urchin (Echinus esculentus) skeletons or shells are often seen as little flashes of colour in the mass of broken shells and pebbles on the shoreline. However, these marine creatures have gone on a long journey to get to this stage.
The common (or edible) sea urchin is found in UK waters and is a powerful omnivorous grazer. They will eat barnacles as well as algae and can ‘graze’ whole areas of the sea bed and rocks clear. A complex structure of plates and muscles supports five chisel-like teeth that they use to scrape food from the underwater surfaces.
Their skeleton, also known as a test is usually bright red with white points where their spines attach. Some may appear pink and others have a purplish blue hue. The white spines are quite short compared to other urchins around the world. Some of the biggest can grow to over 20cm across.
The urchins have long tube feet which are extended when they need to anchor themselves or move around and are usually longer than the thicker spines. Between the feet are small pincers that they use to remove debris. Without these cleaning pincers the urchin would find life difficult collecting debris as it moved.
As with any creature their lives will end. Many will be victims of deep sea trawling and habitat destruction and the species is near threatened. Some will be washed ashore in storms or predated by otters and seals. The fragile shell and spines will remain even after the squishy insides have been eaten or washed away.
Slowly over time the action of the waves will remove the spines from the shell, eventually leaving just the familiar inner shell. To find a whole shell is a special treat on any beach adventure and a treasure from any adventure. The intact shells will have a hole in the top and small hooks on the inside around the base.