Jacob Christian Schäffer FRS, a versatile eighteenth-century naturalist, and his remarkable pioneering researches on microscopic crustaceans

Abstract

Jacob Christian Schäffer was the first to appreciate the morphological complexity of the microscopic crustacean Daphnia. His investigations, published in 1755, provide an excellent example of the difficulties facing those who, for the first time, attempted to elucidate the structure of extremely complicated animals of small size, of which there were no familiar counterparts. Nevertheless he not only revealed many hitherto unsuspected anatomical features but attempted, with some success, to explain their function. Most notably he showed that Daphnia produces a current of water that draws suspended particles into its complex food-handling machinery. An earlier suggestion of how it feeds was completely erroneous and misleading. A pioneer of the comparative method, Schäffer provided an excellent example of how it helped him to understand, if not entirely to resolve, a complicated mechanism. That reproduction can be either parthenogenetic or sexual presented problems that were not resolved for more than another century. Unaware that males exist, and on the basis of seemingly sound, but misleading, observations, he concluded that Daphnia is a hermaphrodite.