Urchin ID

[Fredfish]

First, thanks for another well written article. I must say that you and Eric Borneman have tought me more about my tank and its inhabitants than any other source.

Now the questions. If it is black, has long spines and has a blue ring around its anus, is it always Diadema savignyi? Same question for the orange ring and Diadema setosum.

I have purchased several urchins over the last two years only to watch them cruise through my algae tank and starve to death so I am hesitant to purchase additional urchins without knowing in advance that they will have a non-specialized diet.

That leads to my next question. Are many/most urchins specialized feeders? Or is it just the ones I buy ?

Fred.

 

[rshimek]

Hi Fred,

Let me put the usual caveat... while I am a professional taxonomist, my expertise is mostly in the mollusks.

However, from what I have read, the colored ring definitions that you gave are correct.

For most urchins, there has not been much real work on their diets. This is particularly true in the tropics (temperate urchins, particularly from the Pacific NW, have much more well known diets).

I suspect many of the tropical shallow water urchins are specialized to eat coralline algae (green coralline algae is the glue that forms a reef, so it is everywhere, so many species could get by on it).

However, it appears that even though such diets are specialized in that regard, there does seem to be some diversity of diet in almost all of them. Rock dwelling urchins that are generalized algal predators on non-calcareous algae seem to be pretty much limited to the long-spined clan, though.

 

[Fredfish]

Thanks Ron.

One of the reasons for confirming the ring color thing is that there were some posts on RC a while back saying that the longspine urchin with the blue ring was predatory on corals or some such thing. While I do not generaly trust such posts unless the author is a genuine biologist with some demonstrated knowledge in that area, it was enough to create doubt

Is there any good identification text for urchins?

Fred.

 

[rshimek]

Hi Fred,

No, there is no good identification text for live ones, in general.

Probably the best effort is this site:

http://www.nhm.ac.uk/palaeontology/echinoids/INTRO/INTRODUC.HTM