Belongs to a highly specialized group of freshwater anomuran crustaceans (Aegla platensis) characterized by a flattened, pyriform or pear-shaped carapace, presenting an intermediate appearance between a crab and a small lobster. It features a prominent, sharp rostrum with a well-developed median carina, which is straight or slightly upturned. Its chelipeds (claws) are strongly asymmetrical, with one being visibly larger and stouter, specialized for crushing prey and territorial defense. The abdomen is partially tucked beneath the cephalothorax but retains functional uropods and a broad telson, allowing for rapid backward escape maneuvers. The overall body coloration ranges from olive-green to grayish-brown and ochre, providing highly effective camouflage against muddy and gravelly riverbeds. Adult males reach a carapace length of 18 to 28 millimeters, exhibiting significant sexual dimorphism, as they are notably larger than females.

Geographical distribution: It is widely distributed across the freshwater basins of temperate and subtropical South America. Its presence is well-documented in southern and southeastern Brazil (including the states of Rio Grande do Sul, Santa Catarina, and Paraná), throughout the hydrographic network of Uruguay, in northeastern Argentina (specifically within the provinces of Misiones, Corrientes, Entre Ríos, and Buenos Aires, within the Paraná and Uruguay river basins), and in southern portions of Paraguay.

Habitat: Inhabits lotic freshwater systems with moderate to fast currents, such as montane streams, creeks, and rivers, which are characterized by cool, well-oxygenated, and clear waters. This strictly benthic species depends heavily on heterogeneous substrates consisting of gravel, pebbles, rocks, and accumulated leaf litter. These microhabitats are vital for survival, offering shelter from strong currents and protecting them from visual predators.

Feeding: Exhibits an opportunistic omnivorous and detritivorous feeding strategy, serving as a key processor of organic matter in its ecosystem. Its diet consists of decaying organic detritus, benthic microalgae, aquatic macrophytes, and a variety of small benthic macroinvertebrates, including aquatic insect larvae (primarily chironomids and ephemeropterans), oligochaetes, and small freshwater snails.

Behavior: Displays primarily nocturnal and crepuscular activity patterns, spending daylight hours hidden under large stones, submerged logs, or deep within leaf litter to avoid predation by fish and birds. It is highly territorial and aggressive, with dominant individuals actively defending their shelter sites through complex cheliped displays and physical combat. Unlike true crabs, it moves with great agility in multiple directions and can perform sudden backward swimming bursts by rapidly flexing its abdomen.

Reproduction: Features direct or epimorphic development, entirely skipping the free-swimming larval stages typical of marine decapods. The reproductive period is concentrated during the autumn and winter months, coinciding with cooler water temperatures. Females carry a clutch of 70 to 200 eggs attached to their pleopods beneath the abdomen. Upon hatching, the offspring emerge as fully formed juveniles that remain clinging to the mother´s abdomen for several days before becoming completely independent.

Conservation status: Currently classified as Least Concern (LC) on the IUCN Red List due to its broad geographical range. Nonetheless, regional populations are increasingly threatened by agricultural runoff, pesticide pollution, siltation caused by deforestation of riparian forests, and habitat fragmentation due to the construction of hydroelectric dams.