Studies on Opilioacarida (Arachnida) I. Description of Opilioacarus texanus (Chamberlin & Mulaik) and revised classification of the genera

In a comparative morphological investigation of all groups of mites, a detailed study of the interesting Opilioacarida must be of primary importance. Regarded as partly primitive and isolated, they present on the one hand an important series of characters in common with Anactinotrichida, on the other a somewhat shorter list of characters found also in Actinotrichida. A revaluation of these relationships appeared at this moment highly desirable. According to our present knowledge, Opilioacarida are rare, and the area of distribution is discontinuous. Species are now known from such widely separated localities as Algeria, Sicily, Corfu, Aden, Asiatic Russia, Ivory Coast, Angola, Tanzania (new record), Madagascar (new record), Uruguay, The Argentine, Puerto Rico, Texas, and Arizona. The gaps can partly be attributed to the fact that, as a rule, Opilioacarids must be collected by hand, under stones, etc., a method generally not applied to mites. Besides, adult Opilioacarida are in the field probably often mistaken for immature Arthropods. Certain data (to be published in the following number of the present series) point, however, also to a very localized occurrence. Recently, various contributors have placed valuable material at my disposal, in that way enabling me to start the present series of investigations. Because these materials consist of species that belong to two genera, the extent of the series is provisionally estimated at two papers. The first part of my study on Opilioacarid morphology is connected with my very interesting travel to the United States of America in 1963. While visiting the Department of Entomology of the University of Kansas, Lawrence, Dr. J. H. Camin promised me some material of Neocarus texanu