Fossils of Archaeoniscus suggest that this genus lived in diverse aquatic habitats, including the marine, paralic, and freshwater environments.

While earlier descriptions suggested that it may have had an ectoparasitic association with fishes, some researchers argue that at least two species, A. aranguthyorum and A. coreaensis, lived a benthic free-living lifestyle based on morphological characteristics that are either unsuitable for or unrelated to parasitic behavior.

Reverend Peter Bellinger Brodie first discovered the crustacean fossils from the Purbeck Group in the Vale of Wardour, England.

[6] In 1918, Wilhelm Haack erected a monotypic family Archaeoniscidae and claimed that it is distinct from the suborder Oniscidea based on the large pleotelson, the shapes of antennulae, antennae and uropods.

[7] In 1992, Robert W. Wieder and Rodney M. Feldmann examined various isopod fossils from Austin Chalk in Texas, United States.

Of these fossils, Wieder and Feldmann considered some specimens that are only known from posterior exuviae to belong to Archaeoniscus based on the raised axial node on the pleotelson which they claim to be distinct from almost every other known isopod species.

The head is embedded into the first pereonite (the first segment of the pereion); it also possesses mandibles positioned transversely with a broad incisor process and has globular eyes on its lateral margin.

Archaeoniscus lacks marginal spines on its broad and semicircular pleotelson, the structure formed by the fusion of the last abdominal segment of an arthropod and its telson.

The unmodified ambulatory pereiopods have distinct coxal dorsal articulations, which are distinguishable from modern cymothoids, suggesting that the genus was not suited for ectoparasitic behavior.

[9] A. texanus has significant morphological differences in comparison to other species within this genus, including the presence of a long fifth pleonite, triangular epimeres, shorter pleotelson and more robust uropod.

[6] Archaeoniscus, initially described as a possible cymothoid and now contained in its own monotypic family Archaeoniscidae, has an unclear phylogenetic position within the order Isopoda.