在体螺层基部的开口称为“壳口”。具有前沟或后沟的壳口称为“不连续壳口”或“不完全壳口”，草食性壳口大多圆滑无缺刻或沟，称为“完全壳口”。
活动端用扣具与狗项圈相连的狗链通过线轮壳口与线轮相连并卷绕起来；
The dog chain, the movable end of which is connected with a dog ring by a fastener is connected with the line wheel by a line wheel casing mouth and wound.
如今右撇子的螃蟹懂得调整猎物---让蜗牛的壳尖远离自己的身体而让蜗壳口对着自己的右边。
Modern-day right-handed crabs orient their prey with the shell pointing away from their body and the opening on the right-hand side .
另外，因为无托步枪退壳口非常接近使用者的面部，当废弹壳跳出时使用者感到非常大的声音、气浪和烟尘。
Additionally, because the ejection port on the bullpup rifle is very close to the user's face, the user would feel greater sound, blast and smoke effects when spent casings eject.
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