People raise blackworms pretty much exclusively as fish food but I got some to try and keep for their own sake. They have special adaptations to tangle together into balls that act like a single animal, some of them even functioning as "tentacles" to pull food or "legs" to move them around.
I think that's so amazing and it's so beautiful and relaxing to watch I can't believe they aren't more popular as pets themselves.
Watch the little extra one get pulled into the group near the end c: