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 photos copyright John P. Hoover unless otherwise credited

Some interesting sea urchins not in Hawaii's Sea Creatures
Here's an (unofficial?) Bishop Museum list of Hawaiian sea urchins

Diadema savignyi (Michelin, 1845)
family Diadematidae
     This urchin often has bright iridescent blue lines on the upper surface of its test and is quite rare in Hawai`i. I have never seen a live one here, or even a photo of one taken in the Islands until Pauline Fiene photographed this one off Mau in 2009. At first she thought it was a juvenile Diadema paucispinum, because of its very long spines, but when she saw it again 3 months later in the same location and noticed that it hadn't grown, she began to wonder. Eventually she found a photo of savignyi in Debelius and Kuiter's massive marine invertebrate atlas and realized what it was.

Centrostephanus asteriscus Agassiz and Clark, 1907 ???
family Diadematidae
     I found this urchin under a slab off the Lana`i Lookout, O`ahu, at about 40 ft. Sea urchin specialist Dr. Richard Mooi of the California Academy of Sciences tentatively identified it from a slide as possibly belonging to the genus Centrostephanus. The Bishop Museum species list lists Centrostephanus asteriscus as the only member of the genus present in Hawai`i. Since it is seen so infrequently at scuba diving depths it's possible that its center of population lies in deep water. I saw another one once, off Makua, at about 60 ft.. It had an urchin shrimp in it.

Cory Pittman writes:

I was scanning the recent entries on your site and noticed the photo of Centrostephanus asteriscus. I've also seen it twice. Once was a lone individual under rubble at Honolua bay (around 40-50 ft). The other time was a pair in a hole in rubble that the black coral divers had knocked off a freshly collected colony at the Lahaina docks. Presumably, those came from around 200 ft which would support the suggestion of a deeper distribution.

Metalia sternalis Lamarck, 1816
family Brissidae
    This irregular urchin test was sitting on the sand at about 50 ft. at Makua, O`ahu. It was larger than most other Hawaiian species except the common Brissus latecarinatus, but it appeared to be different. I sent the photo to Dr. Richard Mooi at the California Academy of Sciences. He replied:

The reason that the big urchin is different from B. latecarinatus is that it seems to be a good match for Metalia sternalis. Since some of the identification depends on things like pedicellariae and pore-pair counts, it's a little difficult to wing it from the photo. However, gross matching with sources other than Mortensen (who has remarkably poor image coverage of this important echinoid) strongly suggests M. sternalis (Lamarck, 1816).