brittle star vs. serpant star

The distinction between brittle vs serpent stars is a totally arbitrary thing that we've made up in the hobby - there is no scientific difference between the two. Brittle stars look just like serpents, but their legs appear to have longer bristles, whereas a serpent star has comparatively smooth legs. Behavior-wise, serpents are less prone to hunting other tank organisms that brittles, but both need to be kept well-fed to be completely safe. To be honest, brittle stars are a bit overhyped in terms of their threat...most brittle species won't bother much. The only notoriously bad brittle species IMO is the green brittlestar.