Paedomorphosis and sexuality in Eulohmanniidae (Acari, Oribatida): surprising diversity in a relictual family of oribatid mites Author Norton K, Roy A. State University of New York, College of Environmental Science and Forestry, Syracuse, New York, USA. Author ErmilovK, Sergey G. Tyumen State University, Institute of Environmental and Agricultural Biology (X-BIO), Tyumen, Russia. & State University of New York, College of Environmental Science and Forestry, Syracuse, New York, USA. text Acarologia 2022 2022-09-28 62 4 989 1069 https://www1.montpellier.inrae.fr/CBGP/acarologia/article.php?id=4558 journal article 10.24349/p0b0-usvs 2107-7207 Paedolohmannia n. gen. Zoobank: 2486996C-711A-42D3-ACA1-8D3DB9BA53CD Diagnosis — With characters of Eulohmanniidae (see below). Body cuticle indistinctly colliculate, elevations outlined by fine, sparse punctation; mostly without reticulation of sharply defined, depressed lines. Rostral tectum with deep medial emargination, without mucro; seta exa less than twice length of le . Lyrifissure ip lateroventral to seta f 2 . Sejugal apodeme absent; all extrinsic muscles of trochanter III insert directly on epimere III surface. Gland g4 opening not observed. Anal segment absent from all instars: adanal segment paraproctal in nymphs and adult. Setae ps 1 of larva and ad 1 of protonymph not hypertrophied, similar to other setae of segment. Pretarsi of adult with large lateral claws; empodial claw minute. Palp with vestige of articulation between fused femur and genu, in form of shallow crease. Males frequent. Type species — Paedolohmannia metzi n. sp. Etymology — The genus name is based on a combination of the Latinized Greek paidos (child) with the root lohmannia , which is used in numerous names for early- to middlederivative oribatid mites. It reflects the paedomorphic nature of the type species and is considered feminine. Justification — We justify this new genus proposal based primarily on the complete suppression of the anal segment ( AN ), including its associated setae and lyrifissures. While suppression of AN is widespread in Prostigmata ( Kethley 1990 ), it is rare among Oribatida and Paedolohmannia may represent only the second example. Most oribatid mites have suppressed the primitive peranal segment, which is retained only by several members of Parhyposomata and Enarthronota ( Grandjean 1939d ; Norton and Fuangarworn 2015 ), but we believe some previously proposed losses of AN in Oribatida are incorrect, or are at least equivocal and differently derived, as explained below. The independence of AN and the adanal segment AD () is lost in various groups where fusions occur between cuticular components, i.e., the anal and adanal plates, with common and obvious examples being members of Phthiracaroidea. But in most instances, there is evidence that the segment itself is not lost; this might be clear from the unsclerotized paraprocts of juveniles, or in the continued presence of anal setae or their vestiges. In several genera of the enarthronote family Lohmanniidae Torpacarus (, Javacarus , Euryacarus ) no clear anal plate is discernible and no unequivocal anal setae are present. These represent the culmination of trends in plate fusion and setal reductions that are seen throughout the family, as indicated by the presence of clear intermediate states ( Grandjean 1950b , Balogh 1961 ). Grandjean (1950b) suggested that segment AN is absent in Torpacarus , but we disagree. We interpret the small fifth seta that forms anteriorly on the paraprocts of the deutonymph ( Bischoff de Alzuet 1971 ) as the anterior anal seta; in some other lohmanniids this seta is positioned at the anterior end when the plate is clearly present (e.g., Haplacarus rugosus Mahunka, 1987 ). The trend toward loss of independence of the anal plates from adanal plates, and the regression or loss of anal setae, seems to have been established early in the evolution of Hypochthonioidea , to which Lohmanniidae belong ( Norton 2010 ). But in most instances the segment itself probably does not disappear. In Eohypochthonius ( Neoatrichosus ) , for example, the anal segment clearly appears in the deutonymph, even though the anal plate is vestigial in the adult ( Fernandez 1984 ). This trend suggests the existence of a long-term selective pressure in Hypochthonioidea , which may relate to reducing articulations that are vulnerable to predators, or that represent unnecessary flex points which reduce the efficiency of hydrostatic control. The suppression of AN in Paedolohmannia seems fundamentally different: normal segmental addition is abruptly curtailed and the neotenic retention of a protonymphal segmentation results in paedomorphosis. The hypochthonioid family Psammochthoniidae provided the first clear oribatid mite example ( Fuangarworn and Norton 2013 ) and Paedolohmannia represents the second.