Germ band differentiation in the stomatopod Gonodactylaceus falcatus and the origin of the stereotyped cell division pattern in Malacostraca (Crustacea).

We analysed aspects of the embryonic development of the stomatopod crustacean Gonodactylaceus falcatus focusing on the cell division in the ectoderm of the germ band. As in many other malacostracan crustaceans, the growth zone in the caudal papilla is formed by 19 ectoteloblasts and 8 mesoteloblasts arranged in rings. These teloblasts give rise to the cellular material of the largest part of the post-naupliar germ band in a stereotyped cell division pattern. The regularly arranged cells of the genealogical units produced by the ectoteloblast divide twice in longitudinal direction. The intersegmental furrows form within the descendants of one genealogical unit in the ectoderm. Hence, embryos of G. falcatus share some features of the stereotyped cell division pattern with that in other malacostracan crustaceans, which is unique among arthropods. In contrast to the other malacostracan taxa studied so far, stomatopods show slightly oblique spindle direction and a tilted position of the cells within the genealogical units. The inclusion of data on Leptostraca suggests that aspects of stereotyped cell divisions in the germ band must be assumed for the ground pattern of Malacostraca. Moreover, Stomatopoda and Leptostraca share the lateral displacement of cells during the mediolateral divisions of the ectodermal genealogical units in the post-naupliar germ band. The Caridoida within the Eumalacostraca apomorphically evolved the strict longitudinal orientation of spindle axes and cell positions, reaching the highest degree of regularity in the Peracarida. The phylogenetic analysis of the distribution of developmental characters is the prerequisite for the analysis of the evolution of developmental patterns and mechanisms.