Meeting Abstract

70.5  Sunday, Jan. 6  Centipedes and crayfish � Two extreme modes of sequential segmentation in arthropods CHIPMAN, A.D.; The Hebrew University of Jerusalem ariel.chipman@huji.ac.il

The majority of arthropods generate segments sequentially during embryogenesis, a process usually referred to as �short germ development.� This is in contrast with the well studied process in Drosophila melanogaster, where segments are generated nearly simultaneously (�long germ development�). The way new segments are made in sequentially segmenting arthropods can vary between two extremes, which will be demonstrated by two different arthropod species. In the geophilomorph centipede Strigamia maritima, there is a large pool of cells arranged as an undifferentiated disk, posterior to the zone of segment generation, from which cells are recruited to form new segments. In contrast, in the crayfish Cherax quadricarinatus, there is no pool of cells, and the generation of new segments is coupled with the generation of new tissue through cell division. This occurs in a unique group of cells, known as ectoteloblasts, which act as stem cells at the posterior of the embryo. Despite their phylogenetic distance and different ecologies, the two species share a number of characters relating to embryogenesis, such as large yolky eggs, similar duration of embryogenesis and maternal care until post-hatching stages. Thus, a comparison between them can show how different embryological solutions have evolved for similar problems. I will describe the segmentation process of the centipede, and present preliminary data on segmentation in the crayfish. I will use the comparison between the two developmental processes to discuss how segmentation mechanisms can vary throughout evolution.