Honestly, that whole complex - stereonepthya, neospongodes, lemnalia, paralemnalia - are confused so much in the hobby and even the literature that I can't even say with any certainty that I've ever seen a photo of any of them that I could be completely sure was actually the species labelled.
But from a hobbyist standpoint, there's fortunately only one thing that matters. Some of them will grow without supplemental feeding, some of them won't. As long as you have one that grows without any special effort, there's little need to try to pin down exactly what it is.
That said, if I had to guess, I'd say either stereonephthya or lemnalia, with the proviso that both could be completely wrong. And whatever it is, it's gorgeous.