Unnamed Coral Species C, D and E were originally meant to spawn on the backs of Reefback Leviathans, but C and D were moved to the 'Lost River. it is currently unknown where E will spawn if it does get added.
Although coral and fauna are sorted separately in the PDA, corals are actually animals. This is because they do not make their own food and eat microscopic creatures instead. The "skeleton" of a coral is actually just limestone.