The arthropods are the most diverse phylum of organisms on Earth, and parasitism has emerged as a life style a number of times. Morphological modifications are usually rather minor changes to enhance feeding or attachment, such as in the insects and arachnids. The crustaceans, on the other hand, often take on rather bizarre forms.
Life cycle stages of most parasitic arthropods are fairly typical of their free-living relatives (although there is considerable variation even within the basic arthropod scheme).
As you examine the material, keep in mind that most parasitic arthropods are external and fairly host-specific. Ask yourself how they find their particular host and stay on it, what do they feed on, and how they disperse to new hosts.