Sea urchins are marine creatures that are related to starfish. They have a hard shell called a test that protects the animal’s soft parts. The test is covered by skin and a protective covering of spines. When the animal dies the spines often become detached from the test. 

Sea urchins are herbivores. They use hard jaws to graze on algae on the sea floor. In Bedfordshire sea urchins are most common in Cretaceous rocks, especially the chalk. They are often fossilised in flint, a very hard material. During the Ice Age much of the chalk was eroded away, but the hard flint was left behind as gravel. This gravel can contain fossil sea urchins or sponges

	Conulus, a Cretaceous sea urchin preserved as a flint cast
	Micraster, a Cretaceous sea urchin
	A modern sea urchin with spines still attached
	A spine from a Cretaceous sea urchin preserved in chalk

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