Some of you may have read the heated discussion over the ID of the sea urchins found on Cyrene Reef on the Wildfilm's blog. Dr David Lane who visited Singapore recently told some of the guides that not all sea urchins with an orange anal ring are Diadema setosum, and one of the specimens spotted which has black-and-white stripes on its spines, and has smaller blue spines could be Echinothrix calamaris, while others with blue lines on the test could be Diadema savigyni.
On reading the first blog entry by Budak, I noticed that the specimen in his blog look dramatically different from the previous specimens of Echinothrix calamaris that I have seen. Most importantly from what I've read on several online guides, the orange anal ring is indeed a distinguishing feature for Diadema setosum.
For the second entry by Ria, I remembered I've read that while both Diadema setosum and Diadema savigyni looks rather similar, the former has the orange anal ring with 5 white spots on its test. Coincidently, the book I read was published by Dr Lane and another echinoderm expert.
With the various discrepancies, I see the need to perhaps seek the opinion of other experts to clarify things, though various other volunteers disagree.
While doing my research online, I found a study on the taxonomic significance of test morphology in the echinoid genera Diadema and Echinothrix published in the year 2006. Since the study is fairly recent, and to be published in a journal means it had been scrutinised by other experts in the field, I personally feel this paper is sufficient to shed some light on the confusion on the various IDs.
Update: I just realised many volunteers, including some experienced ones, had thought that the test refers to the skeleton of a dead urchin without spines. Actually, the test refers to the globular shell of the the sea urchin, whether it is alive or not. And the study is conducted on both living and denuded specimens. And one thing for certain, if the study has really been conducted on dead sea urchin tests, then the colours will already be all gone, and they won't be able to even conduct this study in the first place. Just also to clarify that Diadema sea urchins are some of the easiest species to identify in the field, and in fact, from photos if taken correctly to show the anal cone, test other other key features.
According to the paper, the key to identifying the 3 sea urchins and some of their characteristics are:
1. Diadema setosum
Key: Orange anal ring. Blue/green “spot” markings on genital plates.
Other characteristics: Lines of blue spots on test, no apical ring, white spot marking (day and night), no platelets on anal cone.
An example of this species showing the characteristics above is the one which Dr Lane said could be a Diadema savigyni in the cyrene reef blog.
2. Diadema savigyni
Key: Test distinctly circular not rounded pentagonal when viewed aborally. Test (in living echinoids) distinctly black, with a bold pattern of iridophores down the mid-lines of the interambulacra.
Other characteristics: Bold blue lines on test, bold blue apical ring, white spot marking typically at night only while showing small red/brown spot markings during the day, no platelets on anal cone.
An example of this species showing the characteristics above can be found at Poppe Images. Update: Noticed that the link above is inactive. So here's another example from one of my blog entries.
3. Echinothrix calamaris
Key: Ambulacra prominently raised aborally. Genital plates significantly longer than wide (brown colour morph). Ambulacra only slightly raised aborally. Genital plates not significantly longer than wide (white colour morph)
Other characteristics: Green bands on test, periproct is large and brown with white platelets.
An example of this species can be found on my blog.
You may view the entire paper here.
Personally, I never blindly believe in what an expert says, but always verify with a few sources. If you can find the info in a published journal, it's even better since it would have had several peer reviews before it's published - as good as you have consulted with several experts. While this may not mean the outcome will be 100 percent accurate, at least I minimise the chances of learning the wrong things. And also, the experts are not always the first to say that they could be wrong, as we must remember that the experts are humans too, and humans do, and will, make mistakes. The experts know that, and that's why they always have peer review, but unfortunately many lay people assume otherwise.
Asking question is the heart of Science. It's always beneficial to ask what if the one raising the question could be right and do some research on it.
Maybe some people may wonder why I bother to try to find out the correct IDs and correct other people's blog. Many of the volunteer bloggers I know would have probably gotten at least a few emails from me for wrong IDs. And I have received several emails myself from peers who noticed mistakes in my blogs. Perhaps it's because I'm a webmaster by profession, and I'm more sensitive to the power of the Internet. It has a multiplying effect. The people who read the wrong info will just pass it on, and worse still if the reader is a nature guide who may spread the wrong info to his participants, and blogs the wrong info to spread to whoever reading the blog entry.
I'm really no expert myself, so I'm also thankful to those who have corrected any mistakes on my blog, and even more thankful that there are so many scientific sites around these days for me to verify any information that I wish to clarify :)
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