There are two subspecies:[1] The red heart urchin has a somewhat flattened, heart-shaped test made of closely fitting, calcium carbonate plates.

It buries itself in the seabed choosing to inhabit sedimentary areas with sand, silt or coarse coral rubble.

[6] Fifty six tube feet situated near the mouth form a disc and mucus causes the sand particles to adhere to it.

The urchin's growth rate is slow as it is limited both by the amount of organic material that can be extracted in this way and also by the lack of oxygen in the sediment, especially at night.

To overcome this limitation, adult urchins often emerge onto the seabed at night and burrow down into the sediment again next day while juveniles remain permanently buried.

This has a considerable impact on the microhabitat and may be beneficial for the urchin as it results in an increase in the growth of the algae and bacteria forming the film round the particles of sediment.

[6] The red heart urchin has few predators but is sometimes preyed on by stingrays and other fish, loggerhead turtles and the sea star Oreaster reticulatus.