Abstract

The questions raised for the study of marine invertebrate larvae have implications for the evolution of development, the life histories of animals, and life in the sea more generally. These questions began to coalesce in the 19th century around two main factors. The first was the discovery of marine larvae. Through careful observation, investigators detected and confirmed that the development of animals exhibited stages surprisingly different from the previously known adults and adult-like juveniles. Famous examples include the demonstration that barnacles were arthropods because of a shared larval form (Thompson 1830), the characterization of bilateral echinoderm larvae by Johannes Müller (summarized in Huxley 1851), and the unexpected chordate affinities of tunicates. Subsequent studies also demonstrated that adults with similar morphological features could have radically different larval forms and life histories.