I've written about this type of situation many times, and haven't had any problems with using "species", although I'm unclear what you mean by "adjective form". Do you mean like: "What special (emphasis on the "e" rather than on the "c") abilities do you have?"
If you could give us a sample sentence to work with, that would help.
I'm publishing a new book which deals with many competing alien species that are all at war with humans, and I've been frustrated over the lack of alternatives for "species" or "race", so that's a common problem, but I'm not sure there is a specific solution. You might want to make it species specific. Say if the race is Quatrlduck, than the adjective form would be Quatrlduckal. That's pretty straightforward. Otherwise, you're talking about an adjective which describes "having the attributes of a species", which is merely having categories to label specimen by, hardly what you'd be likely to be looking for.
If you insist on an adjective for of species, I'd probably go with special, but modify it so it's clear you don't mean "Ah, isn't he special". I'd add an accent mark, such as "spècial", so readers know the accent is different. Another option is to invent a new word like "specium", such as "What are your specific specium attributes?"
Basically, you're trying to twist English into directions it was never intended to go.
