A Synopsis of the Genera of Beetle Mites with Special Reference to the North American Fauna

Abstract

The beetle mites constitute, it is believed, a natural group of the order Acarina which, because of its close affinities with some of the other groups of mites, is rather hard to limit or define properly. As considered here, the group includes only those mites which possess, in addition to a hard, chitinous exoskeleton, a pair of modified setae on the posterior dorsal aspect of the cephalothorax, known to specialists as the pseudostigmatic organs. Thus limited, the beetle mites have been recognized by some workers only as a family, by others as a superfamily, and by several of our foremost authorities as a sub-order. Michael in his treatise on the group1 considered it as a family, the Oribatidae , which he divided into seven subfamilies. Banks has considered the group as a superfamily, Oribatoidea , which formerly he divided into two families, Hoplodermidae and Oribatidae . Recently he has included the family Labidostommatidae2 also in the superfamily, but this family would not be included in the group as just defined by the writer. Oudemans regards3 the group as one of the twelve of his subdivisions of the whole order, and gives to it the name of Octostigmata . The present writer in 1913, gave a classification of the Acarina4 in which the tarsonemid mites were included with the beetle mites in a suborder called Heterotracheata . The beetle mites were divided into two sections under this suborder, Ginglymosoma and Scleroderma . The former section included the family Hoplodermidae and the latter the families Hypochthonidae, Nothridae , and Oribatidae . Berlese has in the last few years described some interesting new species, which show both the characters of the family Hoplodermidae and also those of the families Hypochthonidae and Oribatidae . These should, I believe, be regarded as the direct descendents of the “connecting links” between these families, and their discovery must necessarily cause us to regard the Hoplodermidae as being more closely bound to the other families than was formerly believed.