i'm glad you asked, i was under the impression that Macrogyrodactylus polypteri is specific to polypterids, but since i wasn't sure, i decided to do a little search, and it turns out there are now 9 described species, and 1 still undescribed. Some of the species were named based on the type host they were found on. e.g. M. polypteri, or M. clarii.
it seems they are host specific. e.g. i didn't see anything saying M. polypteri was found on clarias/heterobranchus catfish, or M. clarii on polypterus. but then again i wasn't look too hard.
Also there are now three species found on Polypterus, with M. polypteri the most common i presume and the earliest known, and M. simentiensis the newly described, and another yet undescribed.
btw CDM, what made you think yours were M. simentiensis and not M. polypteri? i honestly have no clue which is which