Well, she is cute and fluffy. The critter above is a Screffling, a representative of one of the major branches on my fictive tree of life. Sometime in future (perhaps after a series of independent, one-beastie-at-a-time posts, perhaps in one massive infodump) I'll include the whole overarching phylogeny of my various imaginary beasties, but for now I'm not going to attempt something quite so grandiose. Better, I think, to start simply.
So! Screfflings. Screfflings occupy roughly the same position, ecologically speaking, on Gavanna that mammals in general did on Earth during the Mesozoic, or that rodents do today; they aren't rare, exactly, and they do pretty well for themselves, but they aren't about to win any prizes for the largest/fastest/most colorful/most dangerous/highest flying/etc. critter around. Like many Gayenni* beasties, screfflings are capable of adjusting their metabolism between endothermy and ectothermy as conditions demand, and the layer of insulating fur-feathers covering their bodies helps them maintain their body temperature when they're in an endothermic state. Said fur-feathers (the in-world name for them being "screff," hence the name "screffling") are made up of many tiny fibrils, all intertwined and matted together into a hollow, insulating shell. The quick diagram below shows a pretty typical example of a screff.
The darkened patch towards the lower left is where the screff would be rooted into the skin, while the cutaway at the upper right shows the (not terribly interesting) cavity inside. Some species of screfflings have taken this basic form and run wild with it, producing rigid armored plating, loosely connected tufts of fibrils, delicately arcing pennants, and in a few cases even barbed, irritatant tufts that can be dislodged to deter attackers--but the simplest form of screff is by far the most common, and has persisted more or less unchanged for as long as screfflings themselves have existed.
Well. Not much to elevate, instruct, or amuse in the above, I'm afraid--for it to be interesting, I realize one needs to already have some sort of investment in my world, and as it is I suspect this is only particularly enthralling for me. I'll try to have something a bit less abstruse and more interesting next time 'round.
*Of or relating to Gavanna, with Gavanna being the name of my world. I did mention that in the first post, I believe, but Hey, no harm in offering a little clarification.