He was educated for the church, became tutor to a young nobleman, and after several years' travel with him, settled in Copenhagen in 1767, and married a lady of wealth.

The study of invertebrates began to occupy his attention almost exclusively, and in 1771 he produced a work in German on “Certain Worms inhabiting Fresh and Salt Water,” which described many new species of those annulose animals called by Linnaeus aphroditae and nereides, and gave much additional information respecting their habits.

[1] In his Vermium Terrestrium et Fluviatilium, seu Animalium Infusoriorum, Helminthecorum, et Testaceorum non Marinorum, succincta Historia (2 vols.

His Hydrachnæ in Aquis Daniæ Palustribus detectæ et descriptæ (Leipzig, 1781), and Entomostraca (1785), describe many species of microorganisms previously unknown, amongst other dinoflagellates.

He was one of the first to study microorganisms and established the classification of several groups of animals in addition to the infusoria, including Hydrachnellae and Entomostraca, all unknown to Linnaeus.