(a) Cephalothoracic sclerites:

All the cephalothoracic sclerites are to form a single large and continuous dorsal shield. The anterior portion of dorsal sheild is called dorsal plate, and extends over the head as a laterally compressed, serrated process called rostrum.

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At the base of rostrum a pair of orbital notch is found that lodged a stalked, movable, compound eye. Just behind the orbital notch there are two outgrowths, the anterior antennal spine and the posterior hepatic spine.

The posterior region of dorsal sheild is called carapace. On either side of thorax it hangs down freely as branchiostegite or gill cover.

(b) Abdominal sclerites:

Each abdominal segment is covered by separate sclerite and all the sclerites are joined with each other with arthrodial membrane and are movable.

Each sclerite is composed dorsally by tergum, ventrally by narrow bar like plate sternum and the two flap like lateral plates pleura.

Abdominal appendages are connected with pleuron by a small plate epimeron. Tergum and pleura of adjacent segments slightly overlap each other and this arrangement is called imbricate arrangement.

Two adjacent abdominal segments articulate with each other by means of a pair of hinge joints. However, the hinge joints are lacking between the third and fourth segment.