Fossil Collohmanniidae from Eocene Baltic amber, image stacks of type specimens

Image stacks of Collohmannia (Acari: Oribatida: Collohmanniidae) type specimens from Eocene Baltic amber.<i>C. sellnicki</i> sp. nov., <i>C. albertii</i> sp. nov., <i>C. nortoni</i> sp. nov., <i>C. groehni</i> sp. nov., <i>C. kerneggeri</i> sp. nov., <i>C. weiterschani</i> sp. nov., <i>C. clavata</i> sp. nov., <i>C. schusteri,</i> <i>C. pergrata comb. nov.</i>Imaging in transmitted and reflected light was done using a Nikon E-800 compound microscope equipped with Olympus OM-D E-M10-II or Nikon D-7000 digital cameras. The holotype of <i>C. schust</i>eri was imaged on-site using a Carl Zeiss AxioScope A1 microscope equipped with Canon EOS 70D digital camera. Stacks of images, comprising multiple focal planes, were treated for color, digital noise and sharpness with Adobe Lightroom. Confocal laser scanning microscopy (CLSM) imaging was done using Zeiss LSM-880 microscope. Widefield fluorescence imaging was done on Leica DMi8 microscope.To view and manipulate image stacks the following software is recommended: FastStone image viewer (Freeware), FIJI or ImageJ. To view confocal source image stacks (czi) use Zeiss Zen or FIJI. Some of the images were 0.5x pixel-downsampled (_d2 in file name), mind to apply the respective scalebars.For correct scaling, a scalebar file should be applied, pixel to pixel, to the image, irrespective of DPI or PPI in the file headers.This study provides a comprehensive morphological analysis of ten fossil specimens from the genus <i>Collohmannia</i>, found in Eocene Baltic amber, with nine representing different species. Collohmanniidae, a unique monogeneric family of oribatid mites exhibiting characteristics between Mixonomata and Desmonomata, are among the largest oribatids. They feed on leaf litter and present significant sexual dimorphism and courtship behavior, which includes the transfer of nuptial food from male to female. Extant <i>Collohmannia</i> species inhabit isolated mountain forest areas. A fragmentation hypothesis has been proposed to account for their highly disjunctive distribution, suggesting that climate change divided a large forest area previously occupied by a parent species, leading to the allopatric evolution of several species of <i>Collohmannia</i>. However, with the discovery of a significant number of fossil species in Eocene Baltic amber we propose an alternate hypothesis with the Baltic amber forest serving an arena for speciation of Collohmanniidae. According to it, the driving force of speciation was dietary and was based on gut microbiome specificity, reinforced by the female choice during the courtship ritual. In this paper we describe seven new fossil species of <i>Collohmannia </i>(<i>C. sellnicki</i> sp. nov., <i>C. albertii</i> sp. nov., <i>C. nortoni</i> sp. nov., <i>C. groehni</i> sp. nov., <i>C. kerneggeri</i> sp. nov., <i>C. weiterschani</i> sp. nov., <i>C. clavata</i> sp. nov.), re-describe <i>C. schusteri</i> based on study of the holotype, synonymize <i>Embolacarus</i> with <i>Collohmannia</i>, propose and describe the neotype of <i>C. pergrata comb. nov.,</i> and provide a key to all described Collohmanniidae. Together with the hypotheses of speciation we propose verification experiments to be performed on extant <i>Collohmannia</i> mites. <br>