Cornelius Jan van der Horst (11 May 1889, Nieuwer-Amstel – 10 October 1951, Johannesburg) was a Dutch biologist who worked mainly on marine biology and embryology in both the Netherlands and South Africa.
In 1925 Van der Horst was appointed Deputy Director of this Netherlands Central Institute for Brain Research and in 1928 he moved to South Africa where he took up a post as senior lecturer in zoology at the University of the Witwatersrand in Johannesburg.
In 1920 Van der Horst undertook a trip to Curaçao to conduct research into the marine fauna, he had studies so many coral skeletons that he wanted to examine the living organisms.
In his research on acorn worms he demonstrated a thorough knowledge of the literature, as well as a clear understanding of the complex anatomy and morphology of this group, he soon became recognised as one of the leading authorities on the Enteropneusta, eventually having a genus, Horstia, named after him.
He also wrote several chapters in Heinrich Georg Bronn's Klassen und Ordnungen des Thier-Reichs, wissenschaftlich dargestellt in Wort und Bild (Classes and orders of the Animal Kingdom, scientifically represented in words and pictures")[5] and contributed a chapter on spinal nerves to the "Handbuch der Vergleichenden Anatomie der Wirbeltiere ("Handbook of Comparative Anatomy of Vertebrates").