Aspects of embryonic and postembryonic development of the Japanese freshwater crayfish Cambaroides japonicus (Crustacea, Decapoda) including a hypothesis on the evolution of maternal care in the Astacida

Little is known about the biology of the East Asian freshwater crayfish of the genus Cambaroides. Furthermore, the phylogenetic relationships of Cambaroides are controversial. To gain more information about East Asian crayfish and to shed some light on the phylogeny and evolution of freshwater crayfish, some aspects of the embryonic and postembryonic development of the Japanese freshwater crayfish species Cambaroides japonicus are described. The general appearance of the embryo and the growth zone consisting of about 40 ectoteloblasts correspond with the apomorphic pattern described for all other freshwater crayfish species. The occurrence of eight mesoteloblasts is a typical malacostracan character. In addition to the occurrence of freshwater crayfish apomorphies, such as a telson thread, the postembryonic development of C. japonicus follows the ground pattern of the Northern Hemisphere Astacoidea. In particular, some characteristics are in common with the postembryonic development of the Astacidae. These concern the shape of the telson of the juvenile stage 1 and the occurrence of plumose telson setae in juvenile stage 2. Furthermore, the recurved hooks of the hatchlings are lost in the juvenile stage 2, indicating an early independence of the juveniles from the mother. On the other hand, the early appearance of a spermatheca (annulus ventralis) is shared between C. japonicus and the other (American) Cambaridae. The hypothesis is developed that the evolutionary success of the different freshwater crayfish taxa might be related to the stepwise extension of maternal care as an adaptation to the freshwater environment.