Organogenesis

Abstract

This chapter reviews the development of the major organ systems in crustaceans, including musculature, nervous system, circulatory system, digestive system, osmoregulatory system, excretory system, reproductive system, and sensory organs. It describes the morphological unfolding of these organ systems, which generally follows cleavage, gastrulation, and segmentation in the course of ontogeny. Particular emphasis is given to the organ-specific temporal dynamics of development, the onset of functionality, and possible correlations with developmental mode, life history, and ecology. The anatomy and cellular characteristics of developing organs are generally better investigated than aspects of physiology, biochemistry, and molecular biology. Investigations in different crustaceans revealed that the speed of development of the various organ systems varies considerably within an individual and between species. As a rule of thumb, anlagen of the nervous tissue, muscular tissue, digestive system, and excretory organs appear first, followed by the circulatory system. Osmoregulatory organs are formed later. The reproductive organs are the last to emerge and to become functional. The mode of development, behavior, and ecology of the postembryonic stages seem to be major determinants that influence the speed differences of organogenesis. This is reflected by timing differences in development of the digestive system between directly and indirectly developing representatives or species with or without lecithotrophic larvae. Other features of the dynamics of organogenesis suggest evolutionary constraints, such as the delayed development of the nervous system in postnaupliar, relative to naupliar, segments in some species. Mechanistic constraints may be involved in heart development and development of nontransitory osmoregulatory organs.