physiologist who first used the name plankton to describe the organisms that live suspended in the sea (and in bodies of freshwater) and are important because practically all animal life in the sea is dependent on them, directly or indirectly.

Hensen was a professor at the University of Kiel from 1871 to 1911 and led a detailed survey of Atlantic plankton in 1899. He was also known for his work in embryology and in the anatomy and physiology of the sense organs, especially the ear; the cells of Hensen and the canal of Hensen, both within the mammalian inner ear, were named for him.