A new species of trigonotarbid arachnid from the Pilsen Basin of the Czech Republic

1949) are representatives of an extinct group of somewhat spider-like arachnids known from the upper Silurian (Přídolí) to the lower Permian (Sakmarian); see Dunlop & Rößler (2013) for a summary of their localities and stratigraphic distribution. Trigonotarbids are usually resolved in the arachnid clade Pantetrapulmonata (e.g. Garwood & Dunlop 2014) as the sister-group of Tetrapulmonata, i.e. the orders Araneae (spiders), Amblypygi (whip spiders), Thelyphonida (whip scorp ions) and Schizomida (schizomids). Trigonotarbids also share characters with the order Ricinulei (hooded tick spiders), such as an opisthosoma with longitudinally divided tergites, a locking mechanism between the prosoma and opisthosoma and a small claw at the tip of the pedipalp (e.g. Dunlop et al. 2009). Trigonotarbid fossils are characterised by a segmented opisthosoma with eight or nine dorsally visible tergites, most of which are, as noted above, divided longitudinally into median and lateral plates. These animals evidently had mouthparts modified for biting in the form of ‘clasp-knife’ chelicerae (Garwood & Dunlop 2010; Haug 2018, 2020) and were presumably predators in Palaeozoic terrestrial ecosystems. Around a hundred species of trigonotarbid have been described in the literature, of which 70 are currently considered valid (Dunlop et al. 2020). Fourteen of them are known from the Czech Republic, and historical descriptions can be found in Stur (1877), Kušta (1883, 1884), Frič (1901, 1904), Petrunkevitch (1953) and Přibyl (1958). More recent summaries and species descriptions can be found in Opluštil (1985, 1986), with a revision of three genera by Dunlop (1995) and the description of a further new species by Hradská & Dunlop (2013). Here, we describe a new genus and species of an unusually gracile trigonotarbid from the Pennsylvanian (early Moscovian) Radnice Member of the Pilsen Basin.