So, these deep-sea critters are a little over a foot long.
You can find their baby cousins on the beach. Scan the wet, flat sand when the edge of a wave laps up and retreats. If a lot of small holes in the sand appear* as the water drains off, take a deep scoop and gently let the sand fall through the cracks between your fingers. If you’re lucky, you’ll sift out a bunch of wee little isopods about the size of fingernails.
I used to put them in the moats of my sand castles when I was little; every sand castle needs moat monsters.
*(Those holes are caused by critters under the sand breathing out while the sand is still liquid enough to preserve the shape of air bubbles).