Spiropsari

This tiny creature, known as the Spiropsari(spinning fish) uses a rather unique type of movement to travel. Instead of moving its tail horizontally or vertically, it would spin them. This is because of the high density makes moving harder, and spinning its tail, while uneffiecient, is one of the best ways to travel when you are tiny.

These creature eat thermophiles, and travel in groups, like krill shrimps. They travel thousands of meters by riding deep sea water stream, and is one of the main source of food for creatures living in the open sea biome.

Their body is rather simple, consisting of only head and tail. Its fins, which their ancestors previously had, deformed, and turned into "anchor point" for tail muscle(like how our tail bone is now used for anchor point for spine)