I would just see if you can easily remove it. Plus once the fish is out of water with magnifying you should be able to get an idea what it is. I reason I'm hesitant to medicate is all meds to treat argulus/lernia are fairly toxic organophosphates, its like putting bug spray in your tank. You really don't want your hands contacting water/fish after treatment, not to mention affect on the fish itself.
I don't think you can do too much damage removing. Keep in the mind it is close to gill, so be gentle and if it seems like you will do more damage than good; leave be.