There are plenty of stinging organisms in our tank, and they’re not always obvious. Sure, things like anemones and corals use stinging cells (nematocysts) to subdue their prey, which sometimes turns out to be our hands, but there are plenty of other things crawling around in the live rock that can inflict some damage as well. Bristleworms immediately come to mind. These polychaetes are great detritivores, but their bristles can become lodged in a fingertip or two and lead to some serious pain. Sea urchins are another fairly obvious threat, as their spines can easily penetrate the skin and even break off in a finger, leaving intense pain. Other creatures like bryozoans, various snails, and other rock dwellers can cause various skin irritations. Long story short, wear gloves when handling live rock or just tinkering in your aquarium in general. You could bare hand it, but you’re running a serious risk of infection.