Answer :

MattD
Due to their construction, they are often mistakenly equated with species of crustaceans. Scorpios are often considered shellfish due to the fact that they have armor, but actually scorpions belong to the order of arachnids (Arachnida) the size of their ranges from 13 to even over 180 mm (emperor scorpion), living in both the tropical areas (from rainforest the desert regions), as well as high-altitude areas periodically covered with snow.
Pulkit
No scorpions are not crustaceans. It is because crustaceans came from larvae and Most crustaceans are free-living aquatic animals, The crustacean body is protected by the hard exoskeleton which is not in the case of scorpions. 

Almost all the scorpions are arachnids.