The Class Diplopoda has the arthropods known as the millipedes. Millipedes have two pairs of legs per body segment (excluding the first segment that is just behind the head which doesn't have any and the next few which only have one pair).
Millipedes generally have long cylindrical bodies although some millipedes are flattened. Others like the the pill bugs are short and can roll into a ball when threatened.
Millipedes eat decaying leaves and other decaying plant material. Because of this, millipedes are considered detritivores. The secrete compounds onto this decaying mater and then scrap it up with their jaws.
There are about 10,000 species of millipedes in the class Diplopoda. There are 13 orders and 115 families.
The largest millipede is The Giant African Millipede (Archispirostreptus gigas).