Thulian smoolks specialize in iron hydroxide, a precipitate found in the groundwater of the West Mason Caves.
There are two subspecies of Thulian smoolks. The first arose when red smoolks first colonized the entrances of the West Mason Caves. The entrances still had sunlight, so as Thulian smoolks they still photosynthesized. The second developed from individuals which grew farther away from the entrances. Since they had less light to photosynthesize, they became more reliant on iron-eating as a form of nutrition. However, even these Thulian smoolks cannot grow to maturity in total darkness. Thulian Smoolks which grow in total darkness exhibit stunted growth, a papery texture, lessened pigmentation, and a propensity to set aflame. (Not on their own)
(Oops, I depicted the caves like they were solutional limestone caves...maybe the composition is calcarenite? Calcarenite is like both limestone and sandstone.) (Yes, Thulian is supposed to be capitalized.)