I was going to comment to say that horseshoe crabs not arachnids, but form a separate class within the subphylum Chelicerata. However, upon doing some quick research, it seems that the most recent studies do in fact place horseshoe crabs within the Arachnida. I don't think it's completely settled yet, and it certainly hasn't made its way into textbooks.
He's a poet and didn't know it - but his feet show it, they're Longfellows. (One of my Dad's sayings, and apologies to QM. I have no idea about the size of your feet.)
Great quiz, but I would lump bison into cattle, unless of course you're talking about simply domestic cattle. If that's the case, you could also replace it with "wild cattle'', given that including ghaur, cape buffalo, etc would probably be a stretch. That aside it's a fantastic quiz!
I got stuck with "decapoda" thinking "what kind of arthropod has 10 legs?", and thinking of some kind of centipede. Turns out it's prawns.