Aeglidae

Aeglids 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.^[4] The carapace length of the largest species may approach 6 cm (2.4 in), but most are considerably smaller.^[3]

Aeglids are omnivorous, preferring plant matter, but also eating adult insects, molluscs, fish and fly larvae.^[5]

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.^[6]

Mating is preceded by a period of courtship, and does not coincide with moulting, as it does in many other decapods.^[7] The eggs of aeglids hatch as juveniles which closely resemble the adults. They are cared for by their parents and live at the bottom of the body of water.^[8]

Aegla, the only extant genus in the family, contains around 74 described extant species.^[9] Of the 63 species and subspecies described by 2008, two are found in lakes, four in caves, and the remaining 57 are found mainly in rivers.^[3] 42 species are found in Brazil, all restricted to the country's southern and southeastern regions (Rio Grande do Sul alone is home to 24).^[9] Other countries with species are Argentina, Bolivia, Chile, Paraguay and Uruguay.^[3] More than a third of the species are considered threatened,^[3] and in Brazil alone 26 species are officially recognized as threatened, including 8 critically endangered.^[10]

This list contains all the described species as of 2013^[update]:^{[Note 1]}

Haumuriaegla glaessneri is a species known only from fossils of Haumurian age (Late Cretaceous) found near Cheviot, New Zealand.^[13] At the time of its discovery, Haumuriaegla was the only known fossil from the family and the only marine member.

Protaegla miniscula was discovered in rocks of Albian age from the Tlayúa Formation, near Tepexi de Rodríguez, Mexico.^[14]

The family as a whole is thought to have originated around 75 million years ago in a marine environment,^[3] and then entered South America from the Pacific side during the Oligocene.