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Blue-Black Urchin

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description Blue-Black Urchin Overview

The blue-black urchin is the common name for Echinothrix diadema, a diadematid sea urchin distributed across the tropical Indo-Pacific. It has two visibly different spine types: long primary spines and shorter secondary spines, with coloration that can appear black, blue-black, or banded depending on the individual and lighting. As an herbivore that grazes algae, it is part of coral-reef food webs and is chiefly relevant to reef ecology and field identification.

help Blue-Black Urchin FAQ

What is the scientific name of the blue-black urchin?

The blue-black urchin is commonly identified as Echinothrix diadema, a tropical member of the family Diadematidae. It is generally dark or blue-black, with a blue sheen visible on some spines.

Where is Echinothrix diadema found?

Its Indo-Pacific range extends from the Red Sea and East African region across tropical reefs toward Hawaii and other Pacific islands. It is associated with coral-reef environments rather than temperate coastal waters.

What are the two types of spines on a blue-black urchin?

It has long primary spines that provide defense and shorter secondary spines involved in movement and handling the substrate. Those two spine systems are typical of many regular sea urchins, but Echinothrix diadema's uniformly dark appearance helps distinguish it from the banded Echinothrix calamaris.

How does the blue-black urchin differ from Echinothrix calamaris?

Adult Echinothrix diadema normally has fully dark, unbanded spines and a small, dark anal sac. Echinothrix calamaris is commonly recognized by banded spines, although color forms and juveniles can make identification more difficult.

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