Yeah, I was looking for a good candidate. A crustacean makes sense because I have worms and echinoderms already. Most of the exclusively swimming crustaceans are pretty little, though.

I wonder if there’s some kind of small cephelopod that would be good. Otherwise, nudibranches, jellyfish or comb jellies. The bobbit worm might honestly need it’s own tank if it has too much opportunity to catch things.