I have collected both species here, the ranges of reidi and erectus do overlap, but they do not cross breed in the wild, if they did they would be one species, that is the definition of a species, so if they are WC, they are pure bred. As far as appendages, those are dependant on the habitat, if they were caught in the grass flats the coronet is much less developed then when they come from sargassum weed, I have collected them with long coronets in the weed and almost no coronet in the grass flats.
P. Humann gives a great discription of the 2 species and says the easiest way to tell them apart is by the lines radiating from the eyes, erectus has lines (common name- lines seahorse) reidi doesn't have lines. IMO unless they are captive crosses, they are erectus.