I'm told the most probable way deep sea vent critters get from one hotspot to another is intermediate stages at dead whales on the bottom of the sea.

The bit with the ratfish and the crabs reminds me of something really silly I saw on ORCA's undersea camera they had parked off Monterrey Bay for several months awhile back, along with a bit of bait to attract passers by (after a major repair, they put down an entire pig carcass.. THAT provided a lot of entertainment for everything.) Anyway, while I was watching a small hermit crab wandered by, and checked to see if there was anything edible on offer - leastwise it wandered about the tray before the cameras for a bit. As it did, a larger (non-hermit) crab came stalking up and began shoving the hermit crab around. The two crabs duked around for a bit before the hermit crab decided to leave the territory to the larger crab and departed to the right of the field of view. The larger crab stomped back across the field of view in triumph (you could just see it thinking "Hmmmmpfh! Showed HIM!") and nearly ran over a poor ratfish who had just been sitting there minding its own business.