or, they could be like coral, and filter feed mirobes in the air, they come from a dark planet if i remember right so mold and fungus are extremely common most likely, soo hell they could even be fungus stalks with a central system of mycelium in there skull acting as a makeshift nervous system?, maybe the fact they look like skeleton is convergent evolution? (aka when two species evolve in such a way too look extremely similiar even though there from two entirely differnt species/ecosystems)