I'm going to second the Schoutedeni being harmless.
I got bit in the tip of the middle finger adjusting equipment below the water-line.
Just my fingertips were below the water.
They usually know me when my whole arm is in the tank, but a finger was looking a bit too good that day.
All-the-way-out or all-the-way-in is decent advice! A fingertip is not the best idea in afterthought.
It felt like a sharp nip of something on my skin and I swore there was truly broken skin overlooking it repeatedly.
The sensation of the nip went away within a minute or two.
-It was a great reminder to stay alert with the larger ones.