Abstract
The interstitial fauna of gastrotrichs in calcareous and silicious sands of some beaches in southern Florida is described. 18 species are described of which 6 are new to science. Most species were found to eat diatoms. The fauna of gastrotrichs was found to be richer in coarser sands; in fine sands and especially in sulphide containing sands only few species are present. Finally the assumption that the interstitial fauna is cosmopolitic is discussed.