An investigation into the male reproductive system of two freshwater crabs from the Amazon: is there a sperm plug or packet formation?

ABSTRACT The male reproductive system of Amazon freshwater crabs Sylviocarcinus pictus and Dilocarcinus pagei were described and compared in terms of anatomy and histochemistry In addition, sperm transfer experiments of D. pagei with sequential copulations were performed and the anatomy of the seminal receptacle was checked. The anatomy of the male reproductive system of both species is an inverted ‘U’ shape, connected by the testes, from which the pair of vas deferens divided into anterior, median and posterior regions depart. Sylviocarcinus pictus and D. pagei revealed coenospermia, which differed from the families of freshwater crabs in Southeast Asia. The histochemical composition of the seminal fluid is similar in both Trichodactylidae, following the pattern described for most Brachyura. Through the copulation experiments and anatomical results, these animals do not show a sperm plug, but rather form different sperm packs when engaging in multiple copulations with different males.