Read full entry

Echinothrix diadema

For other urchins known as diadema urchin, see diadema urchin.

The diadema urchin or blue-black urchin (Echinothrix diadema) is a long spined urchin from reefs in the Indo-Pacific, including Hawaii. With its spines, the typical diameter is 10–20 cm (3.9–7.9 in).[2] It is generally black or blue-black in colour, and always dark. The spines are closed at the tip; the anal sac is spotted light and dark.

It is active at night, hiding in crevices or under rocks during the day.

It hosts commensal species like the shrimp Stegopontonia commensalis. Saron marmoratus stays close for protection, like many fish of the families Apogonidae (cardinalfish) and Centriscidae (razorfish and relatives).

It differs from Echinothrix calamaris in that the spines are not banded, except in juveniles. Another similar species is Diadema setosum, which has longer spines, the distinguishing feature being the colour of the anal sac.


  1. ^ Kroh, Andreas (2013). "Echinothrix diadema (Linnaeus, 1758)". In A. Kroh & R. Mooi. World Echinoidea Database. World Register of Marine Species. Retrieved 2013-11-23. 
  2. ^ Florent's Guide To The Tropical Reefs: Blue-Black Urchin. Retrieved 12 September 2014.


Creative Commons Attribution Share Alike 3.0 (CC BY-SA 3.0)

Source: Wikipedia

Belongs to 0 communities

This taxon hasn't been featured in any communities yet.

Learn more about Communities


EOL content is automatically assembled from many different content providers. As a result, from time to time you may find pages on EOL that are confusing.

To request an improvement, please leave a comment on the page. Thank you!