Thank you Paul!! Looks like a Eupelte indeed! One more picture here. They were found in algae turfs, but not in mussel beds. This makes sense I guess since the Peltiididae famaly are adapted to live on algae (Giere, 2009)
The second image resembles members of Porcellidiidae more, and the underdeveloped antennules together with the lack of caudal rami suggest it to be a sub-adult at or near the final molting stage.