Teloblasts in Crustaceans

Abstract

The posterior growth zone of the germ band of malacostracan crustaceans is characterized by the occurrence of large ectodermal and mesodermal stem cells, the teloblasts. This stands in contrast to all other euarthropod groups, which lack a corresponding cell type. Teloblasts are perpendicularly arranged to the anteroposterior axis of the germ band. They divide asymmetrically in a stereotyped sequence with the smaller daughter cells being budded in an anterior direction. This way teloblasts give rise to the cells of the largest part of the post-naupliar germ band. The post-naupliar cells of the ectoderm and mesoderm are arranged in a gridlike manner and show a stereotyped cell division pattern. The behavior and differentiation of the teloblasts’ progeny up to formation of serial structures such as intersegmental furrows, early limb buds, ganglion primordia, and muscle precursors are described. Questions like the hierarchy of germ layers, the evolutionary origin and differential role of stereotyped cell lineages, homology issues, and the overall development of crustacean germ discs and germ bands are addressed.