Aeglidae

Aeglidae, commonly known as pancoras are a family of freshwater crustaceans of South America. They are the only fresh water anomurans except for the hermit crab Clibanarius fonticola of Vanuatu. They live between 20° S and 50° S, at altitudes between 320 and 3,500 m (1,050–11,480 ft). Pancoras resemble squat lobsters in that the abdomen is partly tucked under the thorax. The notable sexual dimorphism in the abdomen is related to the behaviour of carrying fertilised eggs on the pleopods. The carapace length of the largest species may approach 6 cm (2.4 in), but most are considerably smaller. The internal anatomy has been described for Aegla cholchol and generally resembles that of other anomurans, particularly galatheoid squat lobsters. The morphology of the antennal gland bladder differs from that in other anomurans in having a twisted tubular structure which was interpreted as an adaption to the freshwater lifestyle. Aeglidae is thought to have originated around 75 million years ago and originally inhabited marine environments. The animals began colonizing South America during the Oligocene.