Beginning with Aristotle 2400 years ago, research on crustacean embryology has a long tradition. Rathke’s 1829 landmark study on the noble crayfish initiated modern approaches. Crustaceans in general—and most of their large taxa—show a great diversity in all stages of their developmental pathways from the zygote up to the adult animal. This chapter describes the various modes of cleavage, gastrulation, germ band formation, and segmentation found in crustacean taxa. Cleavage is either total, partial, or mixed. Total cleavage can be indeterminate, without predictable cell lineage; or determinate, with a stereotyped cell division pattern. Gastrulation modes can also vary to a high degree. One finds invagination, epiboly, immigration, delamination, and a mix of some of these. Likewise, the stages of germ layer separation and the number of cells that initiate gastrulation differ. In yolk-rich eggs, a germ disk forms at the future ventral side of the embryo, and the axes and orientation of the germ are recognizable. Through elongation in the anteroposterior direction by a posterior growth zone and intercalary cell divisions, the germ disk is transformed into the germ band. As a result of a unique, stereotyped cell division pattern in the germ band of malacostracans, germ band growth and the segmentation process up to the differentiation of neuronal precursors and early limb anlagen can be analyzed at the level of individual cells. Recent morphological and molecular techniques allow a very detailed spatiotemporal resolution of developmental processes and they offer new perspectives on long-standing morphological questions.
Increased leaf mesophyll porosity following transient retinoblastoma-related protein silencing is revealed by microcomputed tomography imaging and leads to a system-level physiological response to the altered cell division pattern