Matted filefish are not the most beautiful fish one can keep in a reef tank, but they do in fact eat aiptasia.
Matted filefish (Acreichthys tomentosus).
Matted filefish have a kind of camouflage coloration, and they usually swim with a tilted body position, just like in the pictures. Always looking for food.
Filefish do eat aiptasia, but they also might nip corals, and eat various worms, including feather dusters, although perhaps not as much as copperband butterflyfish would do.
Matted filefish (Acreichthys tomentosus) and its reflection in the aquarium glass.
In captivity matted filefish should be fed chunks of various seafood — I like to feed my fish mussels from a grocery store, just freeze them first for a few days and thaw them before feeding.