Bonner Institut für organismische Biologie,
Universität Bonn

Abstract

Most bilaterian animals rely on specialized organs to eliminate the byproducts of protein and amino acid degradation, primarily in the form of nitrogenous waste. Beyond the Malpighian tubules found in insects, myriapods, and chelicerates, the predominant excretory mechanism among bilaterians involves two distinct processes: filtration followed by modification. Organs that perform these functions are collectively referred to as filtration nephridia. The structural correlates of these processes vary across bilaterians and are closely linked to the organization of their body cavities. In protonephridia, ultrafiltration and modification occur within a single unit, while metanephridial systems are restricted to organisms possessing a coelomic cavity. In this talk, I will examine the evolutionary transformations of these excretory systems and address the question of their homology. In annelids, these organs exhibit a degree of interconvertibility with reproductive structures, revealing an intimate connection between excretion and reproduction. In mollusks, filtration nephridia develop into fully differentiated kidneys. Finally, I will compare these systems with the vertebrate kidney, emphasizing correspondences in structure and development within a broader evolutionary context.