Named so for boring into solid rock, usually limestone or tuff, these urchins continually scrape with their short spines and so-called teeth to accomplish this. These urchins pretty much stay out of sight, and if no rock is available for them to bore into they will burrow into the substrate, wedge down inside or between coral branches, or crawl under or in any space they can find to hide in.
- The Pale Rock Boring Urchin (Echinometra mathaei) is the most common species found in Hawaiian waters, and possibility the Indo-Pacific. Most shallow reef flats in Hawaii are riddled with channels and holes bored by these animals, but they can be found at depths to 50 or 60 feet wedged under branches of Finger Coral. It only grow to a size of about two inches and is typically light greenish-white to gray, reddish-brown, or purple in color. From our experiences with keeping these urchins, they pay very little or no attention to algae.
- The Oblong Urchin (Echinometra oblonga) is closely related to E. mathaei, and apart from its dull black color and slightly more oblong shape, the physical differences between these two species is slight. They occur in the same shallow reef flat habitat, but the Oblong Urchin is usually restricted to depths of less than about 10 feet, preferring the shallow rocky shores that are exposed to constant wave action.
- The Rock Boring Urchin (Echinometra lucunter) might be considered the Caribbean and Gulf of Mexico version of E. mathaei found in Hawaii.
Some common species that inhabit colder water regions are the Red (Strongylocentrous franciscanus) and the Purple (S. purpuratus) sea urchins, which are found along the North America coast from Baja, California to Alaska. The Green (S. droebachiensis) species is found in the eastern Pacific as far north as Point Barrow, Alaska, and southward to Washington. It occurs in the Aleutian Islands and westward to Kamchatka, Korea, and Hokkaido, Japan. In the north Atlantic, it is found on the East Coast of the U.S. and Canada, and in Greenland, Iceland, and northern Europeals.
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