I will try this method when I have time and come back here with the results. Though, I will say one thing here. Most arthropod species likely made up wholly of terrestrial ones, and there is a large number of lesser known marine orders this misses out on.
Presumably, someone who specializes in crustaceans and has observed many obscure crustacean taxa + all the common land arthropod taxa that everyone inevitably comes across has observed the most arthropod orders but may not be in the 10 or even top 100 for arthropod species since those metrics are, again, dominated by terrestrial insects. But this is all just a theory until what you suggest, so stay tuned.
