sentences:  It has a small spine at the bend of the wings.The sexes are identical in appearance; the plumage of fledged immature birds has not been described.The invisible rail is superficially similar to the purple swamphen, "Porphyrio porphyrio", which has recently been found in Halmahera, but that species is larger, with a short, thick red bill and a red forehead shield; it also has purple underparts and a white undertail.