CHIPMAN, A.D.; University of Cambridge, UK: Early development and segmentation in the centipede Strigamia maritima

Early development in arthropods encompasses the crucial stages wherein the body plan is defined and the segmental organization of the body axis is laid out. However, these crucial stages have only been studied in a limited range of arthropods, leaving gaps in our understanding of the evolution of the development of the arthropod body plan. I describe the early development and the segmentation process of the European coastal centipede Strigamia maritima. Development begins with the migration of nuclei to the surface of the egg, which then condense to form an embryonic rudiment, or blastodisc, covering an entire hemisphere of the egg. Throughout early development, the embryo can be divided into two distinct areas; the blastodisc, a round or oval domain of mostly undifferentiated tissue, and the germband, which has a clear A/P axis, and differentiated segments. The germband forms from the anterior of the blastodisc and extends anteriorly as the blastodisc contracts. New segments are formed one at a time at the posterior margin of the germband, where it meets the blastodisc. Segments continue to differentiate after they are formed, with the anterior segments being developmentally more advanced than posterior ones. I also present preliminary data on the gene cascade that organizes the formation of the segments, including possible evidence for the existence of a pair-rule pattern in segment formation.