No idea what it is.. Looks like a type of snail at first glance, or some very nasty disease.
I'd disinfect your tent, and everything around it, if I wear you.. Not just wash it down, but give it a serious scrubbing with something strong enough that you need rubber gloves to handle it. cuz definite possibility of it spreading to the next grow, depending on what it is.
- Don't leave a single surface untouched.. Pots,, scissors, wateringcan, anything else that's been near the tent. Either cleanse it, or burn it.
Can use strong household chemicals, or 99% ethanol solution..
- Ethanol solution for your lamp is preferred. I recommend the stuff used for cleaning electronics boards by repairs shops before they start soldering, as it damp off fast without damaging the board.. Just make sure you get into everything, if it's a disease the risk of it spreading to next grow is too big not to do the a complete rundown of everything. Or you might never see a harvest again.
Tho, could be something else, but why risk it if no one can identify it?