Sulphish are basically giant tardigrades, and are up to 20 centimeters long. They have a thick skin in order to ward off some of the heat.
They have appendages extending out of their backs, which harbour symbiotic bacteria. These bacteria provide most of the nutrients it needs.
The symbiotic bacteria provide most of the nutrients the tardigrade needs. However, sulphish will often eat hardy thermophiles which inhabit the bottom of the lakes.