Extended larval development in the hololimnetic shrimp Macrobrachium pantanalense (Decapoda, Palaemonidae) reared in the laboratory

The postembryonic development of Macrobrachium pantanalense, a freshwater shrimp from central South America, was experimentally studied in the laboratory. In contrast to most other hololimnetic Caridea, this species passes through an extended larval phase with intraspecific variability in the number and morphology of stages. Here we describe the shortest developmental pathway comprising nine zoeal stages, the first post-zoeal stage (morphologically transitional between a late larva and an early juvenile), and an early juvenile with vestiges of larval traits. Post-zoeal development is characterized by a gradual reduction of the natatory exopods of the pereiopods (a larval character) and a concurrent transformation of the endopods to walking legs (juvenile trait). A comparison with the larvae of a closely related, often confused estuarine species from northern South America, M. amazonicum, revealed consistent interspecific differences, especially in the morphology of the fifth pereiopod, allowing for an unambiguous distinction of these two allopatric congeners.