''Colobocentrotus atratus'', the helmet urchin or shingle urchin, is a species of
sea urchin in the family
Echinometridae.
In Hawaii it is known as "hāʻukeʻuke." It is found on wave-swept intertidal shores in the
Indo-West Pacific
The Indo-Pacific is a vast biogeographic region of Earth.
In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
, particularly on the shores of
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
.
Description
This urchin is a deep maroon colour and shaped like a domed
limpet. It can grow to the size of a softball, but is usually much smaller. The upper surface is a mosaic of tiny polygonal plates formed from modified spines to form a smooth mosaic. This is fringed by a ring of large, flattened modified spines. On the underside there is another ring of smaller flattened spines and a large number of
tube feet
Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on br ...
.
Biology
This urchin is usually found on
substrates fully exposed to waves and their associated
abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...
effect, often in groups. It feeds on
periwinkles, other urchins and
coralline algae
Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of ...
.
In a test comparing shingle urchins to other species of urchin, it was found that their ability to withstand being washed away by moving water excelled. A combination of their shape, their flattened spines and particularly the strong adhesion of their tube feet made them three times as resistant as other species such as ''
Echinometra''. This enables them to live on inhospitable wave-battered shorelines.
The Echinoblog
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References
External links
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{{Taxonbar, from=Q868315
Echinometridae
Animals described in 1758
Taxa named by Carl Linnaeus