Tilanatar

Tilanatars are huge, aquatic crustaceans resembling horseshoe crabs, often with plant-life and entire eco-systems revolving around them.
The massive size of tilanatars allows them to part enough mist to survive purely on their own; this, along with their docile, herbivorous nature makes them very attractive to smaller aquatic creatures, living in a symbiotic relationship with eachother as the tilanatar parts the mist, and the smaller creatures eat parasites and plants off of their back.
When tilanatars surface, they could easily be mistaken for small islands.   The name 'tilanatar', is the Urkali name for the creatures, adopted by many as the standard term, though they are sometimes called 'atlas crabs'.