Need a better picture - could be a lot of different types of nymphs.
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"Listen to some of these guys talk, and it's like they were born from their momma's belly with a fishkeeping encyclopedia in one hand and an API kit in the other" (unrevealed).
if it moves lke a catipillar and doesn't have legs its probably a fly larvae. There are many of flies with aquatic larvae. Keep it away from your fish. Almost everything that looks like what you have there is carnivorous and predatory.
It COULD be a dragonfly larva. I got some water lettuce and pulled several of something similar off. Then a couple months later was watching a documentary and saw dragonfly larva and thought that it looked just like the caterpillars I got rid of