Alga, Lamina + Steamroller + Pharos

Alga: They cling themselves to whatever floats nearest to the surface, hoping to get some sunlight.
 
Lamina: Their bodies can lengthen to reach the surface. Some of them can even grow at 10 metres in height, in the right conditions (although, they shrink if they find themselves above sea level.
 
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Steamroller: They live in dark caves, warming them up. They often hang around old mines to find charcoal on which they feed on. Their bodies contain lots of gases, making them lighter than they appear.
 
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Pharos: The evolved form of Lampade. They spend the majority of their life on the coast of the ocean, where their flames guide fishing boats back to the dock.