This is a slate pencil sea urchin. Scientific name is Heterocentrotus mammillatus and the Hawaiian name is ‘uku’ula’ula.

Sea urchins are in the phylum of Echinodermata. They have spiny skin and are recognized by their radial symmetry. Sea stars, urchins, sea cucumbers, and sand dollars are all in the same group.

The internal organs are covered by a calcium carbonate shell. This shell is called it’s test and it is further protected by thick blunt spines known as tines. They connect to the test like a ball and socket and allow the urchin to move. The tines and the tiny tube feet help the urchin move. Urchins will wedge themselves into the reef during the daytime and will move at night. Their mouth is on the bottom of the test and they have five teeth that they use to scrape algae off the reef.

They got their name because when they die, the red bleaches out of the urchin. The tines were then used to write on slate. Very much like chalk. Hence the name slate pencil sea urchin. Who knew that you could write with a sea urchin? How fun!!

This colorful image was taken off a West Maui Beach by the dedicated staff of Ocean Project Maui. They offer custom, private snorkel tours around the island of Maui, Hawaii. Each #COLORSOFTHEOCEAN image you see in our monthly blog, was captured during a private guided snorkel tour. These amazing images, as well as images above and below the water of the clients/supporters are included in every tour at no additional cost.

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