Morphology and taxonomy of Paleozoic millipedes (Diplopoda: Chilognatha: Archipolypoda) from Scotland

Abstract

New millipede specimens from the Paleozoic of Scotland are described, includingArchidesmus macnicoliPeach, 1882, from the Lower Devonian (Lochkovian) Tillywhandland Quarry SSSI and three new taxa—Albadesmus almondi, Pneumodesmus newmani, andCowiedesmus eroticopodus—from the mid Silurian (late Wenlock—early Ludlow) Cowie Formation at Cowie Harbour.Cowiedesmus eroticopodusnew species is placed within the new Cowiedesmidae within the new order Cowiedesmida.Kampecaris tuberculataBrade-Birks from the Lower Devonian (Siegenian) of the Lanark Basin near Dunure is shown not to be a kampecarid myriapod, redescribed asPalaeodesmus tuberculataand placed order incertae sedis within Archipolypoda.Anthracodesmus macconochieiPeach is also redescribed and tentatively placed order incertae sedis within Archipolypoda.Archidesmus macnicoli, Albadesmus almondi, andPalaeodesmus tuberculataare each demonstrated to have broad sternites with laterally placed coxal sockets and paramedian pores containing paired valves. These pores are interpreted as having housed eversible vesicles. Some specimens ofArchidesmus macnicoliandCowiedesmus eroticopodusare male and have a pair of modified legs on trunk segment 8, identified as leg pairs 10 and 11, respectively. The presence of modified anterior legs restricted to segment 8 increases the range of variability known in modified appendage location in male millipedes and compounds existing uncertainty about using the presence of gonopods on trunk segment 7 as a synapomorphy of Helminthomorpha. An affinity between Archidesmida and Cowiedesmida is suggested based on possession of modified legs on segment 8 and Archidesmida + Cowiedesmida is placed along with Euphoberiida in Archipolypoda based on possession of free, broad sternites with bivalved paramedian pores and fused pleurotergites. The oldest known evidence of spiracles is demonstrated inPneumodesmus newmani, proving that the oldest known millipedes were fully terrestrial.