he Fascination of Plankton—— The biologic diversity of living organisms is immense and ranges from simple viruses to multicellular plants, fungi and animals. The term »plankton« summarizes aquatic organisms that predominantly move passively in a water body—as opposed to the term »nekton« that is used for active swimmers including larger squids, fish, and marine mammals.1 Plankton includes a vast array of different organisms that occur in the free water column of water bodies. Planktonic organisms are fascinating, mesmerizing and puzzling at the same time, and the microscopic study of plankton has intrigued researchers and natu-ralists for more than a century owing to the challenges when unknown bi- or multi-phasic life cycles are involved. Many marine larvae were initially described as new species, but much later they turned out to be juvenile stages of already known adult organisms. Plankton comes in all ranges of sizes, from a few micrometers as in unicellular green algae, a few hundred microns to a millimeter as in many invertebrate larvae (e.g. larvae of starfish or phoronid worms), to several millimeters or even a few centimeters as in larger polychaetes, crustaceans (e.g. krill), or fish larvae. Classifications such as nano-, meso-, or mega-plankton have been used for categorizing different planktonic organisms according to their size. It should be noted that organisms grow in their ontogeny, and thus different developmental stages of the same species may be assigned to different size classes of plankton. Another classification can be made according to the systematic affinity of the organism, for instance phytoplankton for planktonic plants, or zooplankton for plank-tonic animals.2Plankton have even inspired naturalists to write numerous poems, most notably the famous Larval Forms and Other Zoological Verses, especially »The Ballad of the Veliger,« by British zoologist Walter Garstang (1868–1949), first published in 1951, two years after his death. Similarly, the dissertation De Salpa by the German poet and botanist of French origin Adelbert von Chamisso (1781–1838) of 1819 revealed and analyzed the life cycle of thaliacean urochordates (a group closely related to vertebrates).3From Live Imaging to 3D Modeling: A Guide to Documentation and Processing of Planktonic OrganismsThomas Schwaha and Stephan Handschuh