August David Krohn (1803–1891) was a Saint Petersburg born zoologist of German origin.
He was the son of Abraham Krohn, the founder of Russia's first brewery, who had left the island of Rügen to serve in the court of Catherine the Great.
According to legend, Krohn is said to have left for Central Europe after losing to his younger brother Leopold the competition for the hand of a Vyborg mansion owner's 15-year-old daughter.
Krohn worked at the University of Bonn on zoology, anatomy and embryology.
He was a pioneer in marine biology and published essential works on Chaetognatha (Arrow Worms) in 1844 & 1853.