#CreatureFeature – Heliocidaris erythrogramma (Purple Sea Urchin)

Sea urchins are spherical with a hard shell covered in spines and urchin is an old name-meaning hedgehog.  

Sea urchins are closely related to sea stars, which can be seen in their adult stage fivefold symmetry. They also move around using tube feet that operate like a hydraulic system using water pushed through their vascular system.  

Purple sea urchins colouration can range dramatically from white to green, purple and even black.

Purple Sea Urchins are endemic to Australia occurring along the southern Queensland, NSW, Victoria, Tasmania, South Australia and Western Australia coastlines. Purple sea urchin inhabit coastal waters between up to 35m preferring a depth of 10m. They are classified as benthic creatures meaning they live on the bottom of the water body they inhabit. Purple sea urchins attach themselves to a range of substrates including rocky reef, stones, sea-grass beds, sandy mud, and in crevices and burrows.

Sea urchins mouths are located centrally on the underside of their body. They are herbivores and actively graze on algae covered rock surfaces, seaweed and sea grasses. 

Photo: Dr Isobel Bennett, The Australian Museum

Adults breed by releasing clouds of eggs and sperm that join to become microscopic larvae. These free swimming larvae drift in the ocean current until they find a good place to settle. The larvae begin to form the hard plates (test) of its body these help it sink to the bottom where it can suprisingly transform into a juvenile urchin in as little as an hour.

Did you know?

Sea urchin eggs have regenerating properties that make them important for medical research and may in fact help to find a cure for diseases such as cancer.


Title photo: Rick Stuart-Smith, Reef Life Survey

Jarna Kendle – Biodiversity Program Coordinator

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