Boreskov

PP‐34been formed already in the earliest Cambrian, i.e. from the beginning of paleontologicallydocumented history of the phylum (Parkhaev, 2008). Other classes, Scaphopoda andCephalopoda, have originated later, by the Late Cambrian – Early Ordovician.2) Gastropods were the most morphologically variable and systematically diverse groupof univalved Cambrian molluscs.3) The major part of Cambrian gastropods was represented by the monophyleticsubclass Archaeobranchia, composed of two orders Helcionelliformes (familiesHelcionellidae, Coreospiridae, Igarkiellidae, Rugaeconidae, Stenothecidae, andYochelcionellidae) and Pelagielliformes (families Aldanellidae and Pelagiellidae) (Parkhaev,2002, 2008).4) The subclass Archaeobranchia was a “base” for further evolution of the classGastropoda, being the ancestor of the larger gastropod branches, namely subclassesCyclobranchia (=Patellogastropoda), Scutibranchia (=Vetigastropoda without Trochoidea,Turbinoidea and Seguenzioidea), Pectinibranchia (Trochoidea, Turbinoidea, andSeguenzioidea + Caenogastropoda), and the group Heterobranchia (subclassesDivasibranchia, Dextrobranchia, Sinistrobranchia, and Opistobranchia) (Parkhaev, 2007).References[1]. Fedonkin M.A., Waggoner B.M. The Late Precambrian fossil Kimberella is a mollusc‐like bilaterianorganism // Nature. 1997. V. 388. № 28. P. 868–871.[2]. Haszprunar G., Schander Ch., Halanych K.M. Chapter 2: Relationships of higher molluscan taxa //Phylogeny and Evolution of Molluscs. Ponder W.F., Lindberg D.R. (eds.). Berkeley: Univ. California Press,2008. P. 19‐32.[3]. Ivanov D.L. Origin and early stages of evolutionary transformation of radular apparatus // Evolutionarymorphology of molluscs. Moscow: Moscow State University Press, 1990. P. 5–37 [in Russian].[4]. Minichev Yu.S., Starobogatov Ya.I. On the phylogenetic relationships of the classes within the molluscanphylum // State of the study of groups of the organic world. Bivalved molluscs. Moscow: PaleontologicalInstitute AN SSSR, 1975. P. 205–276 [in Russian].[5]. Parkhaev P.Yu. Phylogenesis and the system of the Cambrian univalved mollusks // PaleontologicheskyZhurnal. 2002. V. 36. № 1. P. 25–36.[6]. Parkhaev P.Yu. The Cambrian helcionelloid mollusks as a basement of gastropod evolution // ModernRussian Paleontology: Classic and Newest Methods. Moscow: Paleontological Institute, 2005. P. 63–84 [inRussian].[7]. Parkhaev P.Yu. The Cambrian ‘basement’ of gastropod evolution // The Rise and Fall of the Ediacaran Biota/ Eds. Vickers‐Rich P., Komarower P. Geol. Soc. L. Spec. Publ. 2007. V. 286. P. 415–421.[8]. Parkhaev P.Yu. Chapter 3: The Early Cambrian Radiation of Mollusca // Phylogeny and Evolution ofMolluscs. Ponder W.F., Lindberg D.R. (eds.). Berkeley: Univ. California Press, 2008. P. 33‐69.[9]. Ponder W.F., Lindberg D.R. Chapter 1: Molluscan evolution and phylogeny: an introduction // Phylogenyand Evolution of Molluscs / Eds. W.F. Ponder and D.R. Lindberg. Berkeley: Univ. California Press, 2008.P. 1–17.[10]. Salvini‐Plawen L. von. A reconsideration of systematics in the Mollusca (phylogeny and higherclassification) // Malacologia. 1980. V. 19. № 2. P. 249–278.195