The earliest to get on dry land, their gills have changed, taking on some of the functions of lungs and allowing them to breathe on land. Their round shape has allowed for the expansion of the gill chambers; in this they differ markedly from the flat bodies of other crabs.
因為最早上陸，鰓的構造具有像肺一樣的功能，以輔助在陸地上呼吸，體形維持著圓球形，以供鰓室擴充，與其他螃蟹扁平的身材極不相同。