螃蟹大多横行,因而被人们称为“横行介士”,这在动物类群中是独一无二的。螃蟹的头胸部两侧具有五对胸足,除第一对为螫足外,其余四对为步足。由于步足的关节只能左右移动,所以只得靠一侧步足侧向推进,另一侧步足趴地而横行了。此外,由于同侧几对步足前长后短,遇到障碍物时也只? Crabs are mostly transverse and are therefore referred to as “across-the-border”, which is unique among animal groups. There are five pairs of chest feet on both sides of the head and thorax of the crab. Except for the first pair of feet, the remaining four pairs are foot and foot. Because the foot joints can only move left and right, they have to rely on one side to push forward laterally, and on the other side to step and go. In addition, because the same side of a couple of steps before long and short, when encountered obstacles only?