Diverse middle Ordovician palaeoscolecidan worms from the Builth‐Llandrindod Inlier of central Wales

Abstract

Palaeoscolecidan worms are rare, Early Palaeozoic fossils with uncertain affinities within the Ecdysozoa. They are locally abundant in the Cambrian and scattered in the Early Ordovician, but very sparse thereafter. Forty-four specimens have been collected from the Middle Ordovician of the BuilthLlandrindod Inlier of Mid Wales and include well-preserved material assigned to seven new genera, with four additional species in open nomenclature. An additional specimen from the Arenig Pontyfenni Formation of South Wales is also described in open nomenclature. The total demonstrates much greater palaeoscolecid diversity than hitherto suspected for this time. The specimens are preserved as cuticle fragments in shales and siltstones, often of submillimetre size but in many cases with excellent preservation. The level of detail preserved in some is equal to that found in Cambrian phosphatized faunas. The new approach to collecting, and the recognition that this material can yield taxonomically useful information, opens new avenues for palaeoscolecidan research in siliciclastic environments. The new taxa are the following: Radnorscolex bwlchi gen. et sp. nov., Aggerscolex murchisoni gen. et sp. nov., Bullascolex inserere gen. et sp. nov., Wernia eximia gen. et sp. nov., Ulexiscolex ormrodi gen. et sp. nov., Pluoscolex linearis gen. et sp. nov. and Loriciscolex cuspidus gen. et sp. nov. The high diversity, and the taxonomic separation from known groups described primarily from Cambrian carbonates, implies that palaeoscolecidans either diversified significantly during the Ordovician or were taxonomically segregated between carbonate and siliciclastic settings. Palaeobiological findings also include confirmation that some palaeoscolecid basal cuticles were solid and others reticulate, plates (and platelets) could form by lateral accretion, plates were in part primarily phosphatic and in part organic and that in at least some groups, platelet secretion occurred external to plate secretion.

Traces of marine nematodes from 470 million years old Early Ordovician rocks in China

“…They also have only longitudinal muscles and move by lateral waving of the body, being unable to penetrate the substrate peristaltically. Their probable ancestors, palaeoscolecids, are diverse and common fossils in the early Palaeozoic strata, including the Ordovician {e.g., Whittard, 1953;Conway Morris, 1997;Botting et al, 2012). This may mean that some large-size sinusoidal traces may truly represent nematodes or forms transitional to the palaeoscolecids and they should be re-examined more closely.…”

Hadimopanella oezgueli Gedik, 1977: a palaeoscolecidan sclerite useless for taxonomic purposes

“…By contrast, taxonomy of complete scler-12 itomes (Bengtson, 1985) has been achieved based on partial scleritome. Although the ontogeny of palaeoscolecids is suspected to be complex (Botting et al, 2012;Brock and Cooper, 1993;Topper et al, 2010), the transition from juvenile to adult stages is not characterized by any significant change in the shape or size of sclerites. Only the interspace between single plates gradually increases during the ontogeny because of an incomplete development of cuticular structures (Zhuravlev et al, 2011).…”

“…They were common components of Cambrian-Late Silurian marine benthic communities 1997;García-Bellido et al, 2013;Hou and Bergström, 1994;Kraft and Mergl, 1989;Müller and Hinz-Schallreuter, 1993;Zhang and Pratt, 1996). Despite the finding of complete and well-preserved palaeoscolecidan cuticles in the lower Cambrian Chengjiang Lagerstätte of China (Hou and Bergström, 1994;Zhang and Pratt, 1996), the middle Cambrian of Australia (Müller and Hinz-Schallreuter, 1993), and the Lower Ordovician of Bohemia (Hinz et al, 1990), some aspects related to both their phylogenetic relationships with ecdysozoan groups and lifestyle are still under discussion (Botting et al, 2012;Conway Morris and Peel, 2010;Han et al, 2007aHan et al, , 2007bHan et al, , 2007cHarvey et al, 2010;Wills et al, 2012).…”

ATremadocian (EarlyOrdovician) palaeoscolecidan worm from graptolitic shales inHunanProvince,SouthChina

“…; Botting et al . ). Palaeoscolecids were initially thought to be annelids (Whittard ; Robison ; Conway Morris ; Glaessner ).…”

“…; Conway Morris and Peel ; García‐Bellido and Aceñolaza ; Botting et al . ); there are no recorded post‐Silurian occurrences. Phosphatic cuticle fragments of palaeoscolecidans can also be extracted from limestones, especially from Cambrian deposits (Müller and Hinz‐Schallreuter ; Topper et al .…”