Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia

Abstract

Phosphatized palaeoscolecid cuticle fragments of Palaeoscolex lubovae sp. nov., P. spinosus sp. nov., Palaeoscolex sp. and Sahascolex labyrinthus gen. et sp. nov., as well as disarticulated sclerites, are described from the Early Cambrian Sinsk Formation (Siberian Platform) at the Achchagyy Tuoydakh fossil-Lagerstatte. These remarkably well preserved arrays of plates and platelets display ornamentation identical to widely reported isolated sclerites assigned to Hadimopanella, Kaimenella, Milaculum, and Utahphospha. The precise relationship of the Palaeoscolecida to the priapulids or alternatively with the nematomorphs remains under discussion, but suggested is their systematic position within the superphylum Ecdysozoa, comprising moulting animals. some of the described cuticular trunks exhibit distinction between the dorsal and ventral sides: nodular sclerites occur on the dorsal and spiny sclerites on the ventral sides of the worm body. Such a pattern of ornamentation may suggest adaptation for a level-bottom, vagile benthic and probably epifaunal mode of life. The Siberian palaeoscolecids are compared with the type species of Palaeoscolex, P. piscatorum Whittard, 1953, and with palaeoscolecid worms from Australia, Bohemia and China. Sclerites recorded with microplates accreted into the basal brim may support a hypothesis that the more complex sclerite structure bearing a series of nodes was derived from simple small sclerites with single node. The biostratigraphic utility of isolated sclerites remains low, because of the same morphology occur in different sclerites may occur in one scleritome.