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What in holy hell is this?

This is the best picture I could get of a scaly pattern on my left index finger. There's three rows of these 'scales' running down the entire length of the nail. I don't have it on any other finger.

They're barely visible, hence they've been growing at least for however long it takes a nail to grow without me noticing. I can only see them if I catch a bright light at the right angle.

The closest thing I can find to it is the very last picture here (do not click if you're grossed out by horrid nail conditions!), 'longitudinal grooves', except mine are far less pronounced look far more of a regular pattern.

Am I .6% merman?

yeah