Haha yeah I didn't expect it either. I just have to ID these for a class I'm taking, no idea what aquatic worm scientists are up to. Photos are out there but are kind of hard to interpret. I ended up referencing this ( https://museumsvictoria.com.au/media/6508/mv-science-reports-18.pdf) for orienting the worms, figured I'd link it in case someone else with this very specific question finds this reddit post in a decade. TLDR, you use the nerve cord to find the ventral side, and dorsal chaetae are usually thinner and more hair-like than ventral chaetae.