Redescription of the cheloniellid euarthropodTriopus draboviensisfrom the Upper Ordovician of Bohemia, with comments on the affinities ofParioscorpio venator

Abstract

Cheloniellida is a rare but significant clade of artiopod euarthropods, and a major component of Vicissicaudata alongside aglaspidids. The first cheloniellid to be described was Triopus draboviensis, based on a single specimen from the Upper Ordovician Letná Formation in Bohemia. Because this specimen was believed to be missing its anterior, Triopus draboviensis has been the subject of considerable speculation regarding its affinities, with several authors combining various isolated cephalic shields with its trunk. Notwithstanding, Triopus draboviensis has eluded detailed restudy in the 150 years since its first description. Here we provide a redescription of the holotype and hitherto only known specimen of Triopus draboviensis, and describe a recently discovered second partial specimen as Triopus sp. It is shown that the holotype of Triopus draboviensis preserves the complete cephalic shield, while the trunk reveals a likely articulating device, which may represent an apomorphy for Cheloniellida. Further information on the trunk morphology provided by the new specimen has allowed a complete reconstruction of the dorsal exoskeleton of Triopus. An assessment is made of fossils previously suggested to represent the cephalic shield of Triopus draboviensis; while it is shown that none of those fossils can be attributed to Triopus, it is reaffirmed that Drabovaspis complexa likely does belong to Cheloniellida, making Drabovaspis the third cheloniellid genus known from the Letná Formation, after Triopus and Duslia. A revised diagnosis for Cheloniellida is provided, and the recently described problematic euarthropod Parioscorpio venator from the Silurian of Wisconsin is firmly rejected from this clade.

REMAINS OF THE ALIMENTARY TRACT IN THE LATE ORDOVICIAN TRILOBITE <em>DALMANITINA</em> (PRAGUE BASIN, BARRANDIAN AREA, CZECH REPUBLIC)

“…After a long gap, two other taxa, "Nothozoe" barrandei Chlupáč, 1970 and Zonoscutum solum Chlupáč, 1999, were established. Nearly all these taxa have been subsequently re-examined and re-interpreted (see Chlupáč 1988Chlupáč , 1999aRak et al 2009Rak et al , 2013Ortega-Hernández et al 2010;Van Roy et al 2021, 2022. Two new genera of thylacocephalans were described by Van Roy et al (2022). Most of the Letná non-trilobite arthropods, including those with non-mineralised exoskeletons, were collected at outcrops of the Dalmanitina-Deanaspis Association (e.g., Chlupáč 1965;Rak et al 2009;Ortega-Hernández et al 2010;Bicknell & Pates 2020).…”

Not the first leech: An unusual worm from the early Silurian of Wisconsin

“…Arthropods dominate—mainly abundant and diverse trilobites (an undescribed dalmanitid and at least 12 other species; Wendruff et al, 2020a; Gass et al, 1992; Gass and Braddy, in press), crustaceans (including three species of the phyllocarid Ceriatocaris Jones, Feldmann, and Schweitzer, 2015, leperditicopid ostracodes, and the thylacocephalan Thylacares brandonensis Haug et al, 2014), a chelicerate (synziphosurine; Moore et al, 2005), and various enigmatic arthropods. These include Parioscorpio venator Wendruff et al, 2020b, originally considered the oldest scorpion, but probably a cheloniellid-like arthropod with a pair of large raptorial appendages (Braddy and Dunlop, 2021; Braddy et al, 2022, but see Anderson et al, 2021, and Van Roy et al, 2022).…”