Life-history traits of the Amazonian freshwater shrimps Euryrhynchus amazoniensis and E. burchelli (Decapoda: Caridea: Euryrhynchidae)

ABSTRACT The family Euryrhynchidae comprises freshwater shrimps with a disjunct distribution, occurring mainly in the Amazon basin. Basic biological information for this group, which is comparatively recent in evolutionary terms, is still lacking. The present study provides the first morphometric and biological data for Euryrhynchus amazoniensis and E. burchelli, analysing relative growth, sexual dimorphism and patterns of heterochely and handedness in both sexes. Specimens were collected from floodplain areas of two rivers in Manaus, northern Brazil. Individuals were measured for carapace length and for the articles of the chelipeds. In both species, males were larger than females and exhibited proportionally more developed chelipeds. No significant handedness pattern was observed, indicating that the larger cheliped may occur on either side of the body. In E. amazoniensis, relative growth analyses revealed strong sexual dimorphism, with males allocating more energy to cheliped development. Furthermore, the morphological analyses and evidence indicate the presence of different male morphotypes in this species, a pattern commonly reported for other freshwater carideans, but previously unrecorded for Euryrhynchidae. Overall, the results indicate that E. amazoniensis and E. burchelli share morphological patterns typical of other freshwater shrimps but also exhibit evolutionary particularities reflecting unique reproductive and ecological strategies, thereby expanding current knowledge of the biology of Euryrhynchidae.