What are these elegant critters?

[saltyhog]

A friend who's knowledgeable says they're possibly brine shrimp. However, I've never put any brine shrimp in the tank...ever. Only feed frozen food/nori. Tank has been set up most recently 6 years ago. For size reference that glass seam you're looking at is 5/8" glass.

Any ideas what they are and where they came from?

 

[BanjoBandito]

Look like mysid (mysis) shrimp babies from the jerky movement. I've had a tank get them even starting from dry rock. Who knows. Your fish and corals will love em.