贝甲类、枝角类、介形类、蔓足类以及叶虾类甲壳动物的头胸甲特别延长扩大，向身体腹侧弯曲，形成的一块由左右瓣合成的蚌壳形甲壳
The carapace of mollusks, branchiopods, bivalves, amphipods, and leaf shrimp is particularly elongated and enlarged, bending towards the ventral side of the body, forming a clamshell-shaped carapace composed of left and right valves.

内部的壳
The inner shell