Gualtherus Carel Jacob Vosmaer

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Gualtherus Carel Jacob Vosmaer (August 19, 1854 – September 23, 1916) was a Dutch zoologist who specialized in sponges. He was born in Oud-Beijerland; his father, the poet and critic Carel Vosmaer, worked as a clerk at a local court.

Vosmaer studied in The Hague and at Leiden University, where he earned his doctorate in 1880 with a thesis on sponges titled Leucandra aspera and the Canal System of Sponges. In 1882 he went to Naples to work as Anton Dohrn’s assistant at the zoological station. He returned to the Netherlands in 1889 to assist Professor Ambrosius Hubrecht in Utrecht, later becoming a private teacher and lecturer there, and in 1904 he became a professor of zoology in Leiden.

A noted sponge researcher, Vosmaer described many sponge species and studied sponges in the Bay of Naples. He also described sponges collected during the Willem Barents expedition (1880–1881) and the Siboga expedition (1899–1900). The sponge genus Vosmaeropsis is named in his honor.