| The shell around each somite can be divided into a dorsal tergum, ventral sternum and a lateral pleuron. |
| The arched upper part of the ring is known as the tergum, and the more flattened under-part as the sternum. |
| The scutum and tergum, with the few exceptions above stated, are articulated together at a large or open angle. |
| Any particular abdominal metamere usually consists of only two sclerites, the tergum and sternum. |
| In the Achorutidae the head is forwardly directed, the tergum of the prothorax conspicuous, and the spring small or vestigial. |
| On each side the tergum overlaps the sternum, and hangs down as a side-flap, or pleuron. |
