Nearly all species are terrestrial.
Arachnids have a pair of tagmata called a prosoma and opisthosoma.
The prosoma is partially or completely covered with a carapace-like shield. The opisthosoma may be segmented or unsegmented. Animal Diversity . Brusca, R. C., and G. J. Brusca. Pearse, V., J. Pearse, M. Buchsbaum, and R. Buchsbaum.