If I was ever going to get into aquariums, I’d focus on the invertebrates. Maybe a bobbit worm and some brittle stars, and something paleagic but I’m not sure what yet.
Maybe shrimp of the group mysidacea? They swim a lot, don’t know if they’re easily available though. I think you can buy them as feeders.
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.