New armoured scalidophorans (Ecdysozoa, Cycloneuralia) from the Cambrian Fortunian Zhangjiagou Lagerstätte, South China

Abstract

Although molecular studies estimated that cycloneuralians might have originated in the Ediacaran Period and diversified in the early Cambrian, it was not until 2014 that they were first reported from the Cambrian Fortunian Stage. To date only two species and five indeterminate forms have been described. Here, we report new three‐dimensionally phosphatized microfossils of cycloneuralians from the Fortunian Zhangjiagou Lagerstätte, South China. Two new genera and species, Qinscolex spinosus gen. et sp. nov. and Shanscolex decorus gen. et sp. nov., and Indeterminate Forms 1–7 are described and tentatively assigned to total‐group Scalidophora, greatly increasing the diversity of the Fortunian cycloneuralians. These Fortunian cycloneuralians have diverse cuticular spines, plates, and spinose sclerites of various sizes on the trunk, thus assignment of co‐occurring fragmented trunk parts or disassociated spines or sclerites to a specific species is currently impossible. Some of the Fortunian cycloneuralians might have reached a centimetre in length; they may have been temporary meiobenthos in their juvenile or younger adult stages, only joining the macrobenthos when they reached macroscopic dimensions. It is proposed that an introvert with hexaradially symmetric and internally hollow scalids might be the plesiomorphic state for cycloneuralians.

Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms

“…Live specimens of Priapulus caudatus were collected near the Kristineberg Marine Station, Sweden (see details of locality in [58,59] 1c,d), but elsewhere it has a wrinkled and more irregular appearance (electronic supplementary material, figure S4(e)). PER fragments display the same external morphology as that of 3D-preserved scalidophoran worms described from the same biota by previous authors (especially Indeterminate Form 1) and consisting of an annulated trunk lined with small and large scalids, a proboscis, a mouth opening and a tail part [38,60].…”

“…All SEM images except (h) and (l ) obtained by using synchrotron radiation X-ray tomographic microscopy. Anterior -posterior orientation based on complete specimens described by Eopriapulites sphinx [37], Eokinorhynchus rarus [38], Qinscolex spinosus and Shanscolex decorus [60]. an, annulus; ant, anterior part; fu, furrow between annuli; ls, large spinose sclerite; pos, posterior part; ro, reticulated ornament; ss, small spinose sclerite; vo, void.…”

Introvert and pharynx ofMafangscolex, a Cambrian palaeoscolecid

“…Because six-fold symmetry is not inherent to the function of the introvert, this detail is less straightforward to attribute to convergence. A hexaradially arranged introvert was likely the primitive condition for Ecdysozoa: not only does it characterize all ecdysozoans from the Fortunian (earliest Cambrian) period (Liu et al 2014(Liu et al , 2019, but its vestiges are apparent in the majority of extant phyla, including stem-and crown-group loriciferans (Sørensen et al 2008;Peel et al 2013), nematomorphs, larval nematodes (despite the lack of introvert armature) (Maas et al 2007) and certain panarthropods, in the form of the six oral papillae of Aysheaia (Whittington, 1978) and the six oral plates of tardigrades (Boesgaard & Kristensen, 2001;Biserova & Kuznetsova, 2012;Guidetti et al 2013).…”

Caught in the act: priapulid burrowers in early Cambrian substrates

“…They are abundant in Cambrian Konservat-Lagerstätten (e.g. [15,16]) and as minute phosphatized larval forms [17,18]. Complete scalidophoran worms are rarely known outside the Cambrian Lagerstätten, typically being inferred from the presence of characteristic sclerites such as Hadimopanella and Milaculum (e.g.…”