Of course there is such a job. At the zoology research center(which by the way is a big joke because they do not have the neccesary equipment so will never discover anything) there is a guy who studies ants(antologist?! 😆 😆 )
I am not sure it would have a name: you would probably call him a zoologist who studies crustaceans

It may be such a job, but i sincerely doubt it. Not sure though…

Well most crustacians are marine so they go to the marine biologists/ecologists, and do not have an official title as such, as for terrstrial arthropods insects are covered by Entomologists(from Greek ἔντομος, entomos, "that which is cut in pieces or engraved/segmented", hence "insect", logos, "study") your ant studying friend would be a Myrmecologist (Greek: μύρμηξ, myrmex, "ant"; and λόγος, logos, "study") biologists that study mtes are known as Aracologists (Acari "mites" logos "study")

but most Scientists who study these organisms usually count themselves as Ecologists, Biologists, Molecular Biologists or Zoologists, depending on what their area of study is

Hope this helps a bit

Duncan