I recently bought a urchin that dies one day after I put it in the tank, it dropped all its spines and died. Also about 3 months ago I bought an urchin that did the same thing. I can't figure out why they are dying. Does anyone have a clue of why they might be dying.
I'd put a small heater in the container you are drip acclimating in. Urchins are very sensitive to changes. This goes for all urchins.
If the volume is too small for a heater you can place a small container inside a larger container of water with a smal heater. This will keep your temp good and increase the chance your urchin will survive.