my understanding is the zig zag yellow tail eel is Macrognathus pancalus which max out around 8" and zig zag marbled eel is just a common name for the regular zig zag eel which is Mastacembelus armatus which max out around 36"
there are actually a couple sometimes labeled or mislabeled zig zag that is the big problem with common names, sometimes drastically differently sized and behaving fish can be called the same thing. An example would be the "Burmese Tire Track eel" I bought that ended up being a Black Spotted Eel
How do you tell if you have a true zig zag? I have what was labeled as a zig zag, he's about the same size as my senegal bichir right now so like 7 inches. Saw a tire track in the store yesterday which was visibly different looking than mine, but I've heard they can look totally different but not be true zig zags