Any Urchin Experts..

[Rin]

I had a 2" dia. pink urchin with very short spines. He had been in the tank for about 2 weeks. During the day a few days ago I noticed him making his rounds on a particular piece of rock that he seems to fancy. After lights out that night (some 8 hours later) I was doing my flashlight bit to watch the critters that come out at night. I found his test. No spines, no innards, just the test. It was perfectly clean, inside and out. Has anyone heard of this before?

Water params:

Ammonia, Nitrates, Nitrites, Phos: Undetectable
Calc: 500+
Alk: 5.5 dKh
Average temp: 82 F
Salinity: 1.025 (measured at 75°F)
pH: 8.4

Inhabitants:
Page Ranking maroon clowns
Long tent. anemone.
Page Ranking Fairy Wrasses
Purple Tang
red serpent star (8")
unknown, very skinny brittle star (not green)
2 serpent cowries
a couple blue leg crabs
all sorts of astrea snails
2 cleaner shrimp

I also suspect I may have a mantis, but I've never lost any inhabitants to it. I just hear the clicks. The mantis trap has never caught him, either.

Thanks,

[scubadude]

I have no idea...you mean it looks like a ball w/no spikes? Im not sure I understand what you mean by you found his test.?

[Rin]

The 'test' is the skeleton of an urchin. It's the golf ball looking shell with a hole on the top and another on the bottom.

Whatever got him left only the skeleton behind. I have a very impressive amphipod colony in my tank but I don't thing that they are numerous enough to strip a dead urchin in a matter of hours. It's also possible that there may be a bristle worm or two in there, but I haven't seen one for almost 10 months now--and I've been looking.

Speaking of which, anyone have any bristle worms they don't want? I've been too lazy to order a refresher pack.