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DescriptionA reddish-brown coloured heart urchin that is longer (7 cm) than wide. The 'test' (calcareous skeletal plates, joined together to form a complete shell) is covered in mobile spines, which are coarser and sparser in comparison with Echinocardium species. Particularly characteristic of Brissopsis lyrifera is a narrow band of ciliated dark spines which rings all five ambulacra petals on the upper surface. It is the only heart urchin likely to be found in muddy sediments.