User blog comment:Jamintheinfinite/Subnautica Creature Evolution/@comment-28450065-20180529093931/@comment-29172324-20180530144832

"The abundance of Stalactites suggests that these caverns were dry-standing for several million years, only later being flooded presumably when the ceiling collapsed due to erosion" - Jelly Shroom page.

Due to this I didnt bother putting the crab snake with them because it most likely evolved differently. The crabsnake is an eel though and the other eels were related and the river prowlers data bank does say genetic overlap with other eels. So it could be possible but I'm not so sure.