Itty Bitty Diadema urchins?

[Ruth]

They definately serve as a not too gentle reminder not to plunge your hand into the tank without thinking! I just finished jumping around holding my thumb because I did just that and managed to ram a spine up my thumbnail
They do encourage the spread of coralline - particularly on the glass viewing areas of my tank.
Right now I don't like mine very much as my stupid thumb (yes attached to an equally stupid person) is still throbbing but most of the time I find it a very interesting creature and they do a good job on pest algea IMO. If only it would get a taste for aptasia and majono!

[Delphinus]

Well, a month in, and not so itty-bitty anymore. 1.5" tip-to-tip at purchase time, now easily >3".

Here are some pics, you can sorta see the blue spines I was referring to earlier. They vibrate like CRAZY.

Definitely neat stuff ...




Added bonus of catching at least 3 pests as well in these shots.