The Heart-shaped Urchin has a world wide temperate distribution. In Australia its distribution ranges from Sydney around the southern shores to Western Australia, including Tasmania. It is also common on European and American coastlines. However, the Australian form only reaches half the size of those found in Europe. (NSW, VIC, TAS, SA, WA)
This urchin is very distinctive because it has a furry, flattened shape. It is not radial, but has a bilateral symmetrical heart-shape (one half is the mirror-reflection of the other). It grows to a length of 45-60 mm.
Due to its irregular shape, the mouth lies towards the front end on the undersurface in a deep depression. The test front-end is also notched, while the hind-end is vertical. The perforated plates on the upper surface, which have tube feet, vary in size to create an unusual five-leafed petal-shape design, which is called a petaloid pattern. The petals are wide and fairly shallow. The pattern is made up of twin rows of holes, through which the hydraulically operated feet extend. These ambulacral plates lie in a furrow. This species can be distinguished from other species of heart-echinoid by not having a row of fine spines around the petal-like shape marking. Tube feet, which are called ambulacra, are also found on the under surface.
The spines form a dense coat. Those on the upper surface are short, being only 2-3 mm long, and are curved with a spatulate (spoon-shaped) tip.
The Heart-shaped Urchins' brittle and easily broken test is creamy-white to light buff in colour. The spines are white or silver-grey. The tube feet are light brown and have a hairy appearance.
Ecology/Way of Life:
The Heart Shaped Urchin is most commonly found in estuaries. It may also be found on very sheltered ocean shores. It is usually found buried in sand at and below low tide level, down to 230 metres.
It shelters in sand by rapidly excavating a burrow with its long spines that have flattened tips. It can form a protective burrow a few centimetres below the sand surface by using slime to partially cement sand grains together to form a small protective cave. It is thought to pass sand and detritus through their bodies and extract the contained food.
Interaction with Humans/Threats:
Because the Heart-shaped Urchin is mostly an estuarine dweller, major pollution to coastal estuaries may form a potential threat.
Bennett, I. (1987). W.J. Dakin's classic study: Australian Seashores. p. 364, Angus & Robertson.
Davey, K. (1988). A Photographic Guide to Seashore Life of Australia. p. 132, New Holland Press.
Clark, H.L. (1946). The Echinoderm Fauna of Australia: Its composition and origin. Carnegie Institution of Washington. Publication 566. p. 382. Washington, D.C.
Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p. 367, Reed.
Shepherd, S.A. & Thomas, I.M. (1989). Marine Invertebrates of Southern Australia. pt. I. p. 451, South Aust. Govt. Press.
Text, map & photograph by Keith Davey.
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