I also got several diadema sp. urchins on the carribean aquacultured
live rock I bought. Two of them are friendlier sorts, but this one
pictured at the top of my page (the one with white bands on the spines)
occasionally nibbled on corals. I caught him nibbling on an acropora
frag. The damage was small (just on one tip) and healed quickly, but I
didn't want things to get worse. It's now living in my quarantine tank,
which has quickly become my "unwanted critters" tank.

http://www.atreis.com/sw-critters.html

Eric
http://www.atreis.com/

david wrote:
I looked up teh urchins on the web. They look more like diadema urchins.
The spines are relatively short with a purple hue. It looked something like
a reef urchin, but it did not have the round white bad at the base of each
stem. I have been wondering why I have been losing coraline, I assume these
guys are not helping matters.
"Pszemol" wrote in message
...

"david" wrote in message

ink.net...

I bought live rock for my new tank about 1.5 months ago. (Carribean
Aquacultured) I noticed a couple of urchins came with the live rocks,

but

now I have seven. Are these creatures a pest I need to worry about? I

read

they eat algae which is fine by me, but do they do any damage to other

reef

creatures?

What urchins are they? Diadema? Tuxedo urchin?
The second is not growing large and is recommended for a larger reef tank.

It is rather unlikely they spawn in your tank... and if so,
there is even more unlikely their larvae survive pumps/filters.
Most likely, tiny ones come with the rock and you did not noticed them.
Now, when they grown, they are more visible :-)