The sentence you wrote, "Hiding in the stinging arms of a sea anemone, clownfish feel safe," is grammatically correct.
Here's why:
- Starting with "Hiding in the stinging arms of a sea anemone," is a participial phrase that describes what the clownfish is doing.
- Clownfish feel safe. This is the main sentence that tells us the effect of hiding there.
- The sentence flows well and uses correct grammar.
So, your sentence is good to go!