User blog comment:Jamintheinfinite/Subnautica Creature Evolution/@comment-28450065-20180323194412/@comment-28450065-20180323230530

Expanding on this, I see potential for relation between the Crabsquid and Cave Crawler. The blue section on the Crawler's topside is described as a "Gas exchange membrane", which could be similar in structure to the Crabsquid's inflated membrane. And there are so few invertebrates on this planet that ones with such similarities are bound to have some relation.

The Reefback is the only oddball amongst the invertebrate animals.