Karl Gottlieb Grell

Karl Gottlieb Grell (28 December 1912, Burg an der Wupper – 4 October 1994) was a German zoologist and protistologist, known for his work on Trichoplax.

Karl Grell received his doctorate (Promotion) in 1934 from the University of Bonn, for a dissertation on the digestive tract of the common scorpionfly (Panorpa communis). Subsequently, he worked primarily on unicellular eukaryotes and the metazoan Placozoa. During World War II, he was assigned to an anti-malarial unit in southeast Europe.

Grell authored a German-language textbook on protozoology, Protozoologie (1st edition 1956, 2nd ed. 1968), published in English as Protozoology in 1973. From 1959 to 1983 he was a co-editor for the Archiv for Protistenkunde. In addition to his work on Trichoplax, he was known for his research on life cycles of the Foraminifera. and was an Honorary President of the IX International Congress of Protozoology in Berlin in 1993.