This chart appears to place a copepod (1) with parasitic representatives of the order Isopoda. The Suborder Cymothoida and some other Isopod families parasitise as ectoparasites grazing on mucus and skin or as endoparasites sitting in the mouth/pharynx of a fish collecting food. this chart shows some common body forms. note how the legs are repeated at each segment compared to those of amphipods which are modified for different tasks on different segments (2-8).
Arthrostraca was an order that included all species of Isopods and Amphipods because of their superficial similarities. This combination of two groups was retained within a newer classification scheme as Edriophthalma and a sister taxa Mysidacea which have since been rejected in favour of the order Peracarida which encompasses all members which were previously in these two groups. This chart shows the nervous system (blue), circulatory organ of the open blood system (pink), alimentary canal (yellow), digestive glands (orange) and brooding eggs under flattened segments of limbs (grey circles in 2 & 6).