Gecarciniae is a family of true crabs that are adapted for terrestrial existence, commonly known as land crabs. Similar to all other crabs, land crabs possess a series of gills. In addition, the part of the carapace covering the gills is inflated and equipped with blood vessels. These organs extract oxygen from the air, analogical to the vertebrate lungs. Adult land crabs are terrestrial, but visit the sea periodically, where they breed and their larvae develop. Land crabs are tropical omnivores who sometimes cause considerable damage to crops.