One of two groups of crustacean to become terrestrial. Less than 15mm in length and varying widely in appearance. Heavily-armoured flattened bodies, 7 pairs of legs, 2 pairs of antennae (one pair more prominent). Will roll into a ball to protect itself from predators. Found in dark and moist environments such as leaf litter, compost heaps, under rocks and logs. Eat decaying vegetable matter and fungi. Predators are mainly other invertebrates.