This will be the final part of my worldbuilding concept: Today I want to discuss the Final Consumers, as well as the Decomposers of my ecosystem.
Final Consumers
Leviathans are the dominant intelligent species living on Europa. They are the largest members of the class Multibracchia, growing up to be around 15m tall. Their last common ancestor with other members of their class was around 10 million years ago, from which point they evolved away from being free-swimming, instead using their two front tentacles to traverse the ocean floor, leaving the other four free for the usage of tools.
Their beak has moved from the centre of their tentacles, to the front of their head, giving them a forward-facing appearance similar to us humans. The fins on the side of their head serve no purpose anymore, though the size and shape hints at the origin of the Leviathan; longer ones indicating someone from abyssal regions, shorter ones indicating at someone from mid-level regions. Their skin tones range from shades of orange to red, which seems to hinge on the depths they settle in and less so actual genetics. Leviathans have a very complex system of language – using bioluminescent signals made with the spot atop their heads to communicate. Brightness, duration (not only of the signal itself, but also its brightening and fading) and fluctuation play into it.
They have settlements all across the mid-level oceans of Europa, built on the foot of large-scale vents where rich ecosystems have been established. Here they have built a form of agriculture; farming Iron Jaws, the much larger relative of the Iron Beak (and comparable to the Giant Clam on Earth). They also keep livestock in the form of Sea Maids; a domesticated form of the Sea Nymphs – this sub-species has completely atrophied fins and is much to heavy and slow to re-enter the wilderness, however. Leviathans also spread out to the cliffs bordering on the abyssal depths, where they hunt Shell-Breakers and other large Cancernatans in so called “hunting villages”.
As it seems they’re still in the early stages of civilization. Though it is unknown to which degree they will be able to develop technology, given that their circumstances are very different to ours as they are confined to the depths of the ocean.

Decomposers
Though the Depth Strider may look very imposing – being about the size of an adult human man – this member of the order of Reptator acts mostly as a scavenger, eating dead and decaying soft-bodied organism they find in shallow to mid-level oceans. On occasion they are also known to eat slow-or unmovingLaminaferrealike Iron Beaks; sticking their long arms into the stone cracks, where they reside in and prying open their shells. Some sub-species have also evolved to eat Floaters, who they catch by climbing up the vents and grabbing them out of the water.

Boneyard Crabs are part of the Armaturatus phylum, distantly related to the White Bristle Crab. They evolved away from being filter feeders, instead turning into scavengers that can be found on the abyssal ocean floor. They feed on the bodies of all matter of large marine animals; from Sea Nymphs to Black Phantoms. They play a valuable role in the ecosystem by preventing the accumulation of decaying matter – they are considered the clean-up crew of Europa’s oceans.
Once a body sinks all the way to the bottom they show up in droves, often hundreds of them crawl out from all sorts of caves and crevices and pick skeletons and exoskeletons completely clean with their two sets of pincers.










































