The Natural Classification of the Rhombognathinae (Acari, Halacaridae)

Abstract

THE Rhombognathinae are a group of herbivorous Acari inhabiting intertidal and shallow subtidal marine and estuarine waters. The group is cosmopolitan in distribution, although some of the genera are not, Rhombognathides Viets 1927 and Metarhombognathus Newell 1947 being known at present from only the temperate North Atlantic Ocean and adjacent subarctic or arctic waters.1 The genus Rhombognathus Trouessart 1888 is certainly cosmopolitan, and the genus Isobactrus Newell 1947 is probably so, being known from the North Atlantic, Adriatic Sea, the Kerguelen Archipelago, and the North Pacific Ocean. The latter record for the genus Isobactrus is based on undescribed species from the western United States and the Aleutian Islands. The subfamily was erected by Viets (1927, pp. 87-89) to include the single genus Rhombognathus, which was divided into three subgenera: Rhombognathus s. str. Trouessart 1888, Rhombognathides Viets 1927, and Rhombognathopsis Viets 1927. The subdivision was based solely on the number of claws on the tarsi. In the course of studies on the Halacaridae of eastern North America, the present author (1947, pp. 25-33) developed a new system of classification which produced a more natural grouping than Viets' system, and the four natural groups were considered to constitute four distinct genera. At that