Ticks and mites are actually arachnids.
Arachnids are a class of joint-legged invertebrate animals that include spiders, scorpions, ticks, and mites. Ticks and mites belong to the subclass Acari within the class Arachnida. They are closely related to spiders and scorpions but have distinct characteristics that set them apart, such as their smaller size, specialized mouthparts for feeding on blood or other fluids, and often parasitic lifestyles.
Crustaceans, on the other hand, are a separate group of arthropods that include animals such as crabs, lobsters, shrimps, and barnacles. Insects and myriapods are also arthropods but belong to different classes within the phylum. Insects are classified under the class Insecta, while myriapods belong to the classes Diplopoda (millipedes) and Chilopoda (centipedes).