Content uploaded by Pavel Parkhaev
Author content
All content in this area was uploaded by Pavel Parkhaev
Content may be subject to copyright.
A preview of the PDF is not available
On the genus Auricullina Vassiljeva, 1998 and shell pores of the Cambrian helcionelloid mollusks
Abstract and Figures
The genus Auricullina Vassiljeva, 1998 and its type species A. papulosa Vassiljeva, 1998 are redescribed based on new well-preserved material, which allows me to revise the generic diagnosis and
greatly add to the morphological characterization of the type species. A new species, A. granulosa sp. nov., is described from the Botomian of Australia. The synonymy of the taxa is improved. The morphology and function
of shell pores in Cambrian univalved mollusks are discussed.
Figures - uploaded by Pavel Parkhaev
Author content
All figure content in this area was uploaded by Pavel Parkhaev
Content may be subject to copyright.
... Specialized cellular extensions, known as caeca, are present in the delicate shell tubules of various mollusk lineages, e.g., extant bivalves, gastropods, polyplacophorans (chitons), 28 and Cambrian helcionelloid mollusks. 29,30 Similar structures, called punctae, are also a characteristic feature of the calcareous skeletons of brachiopods and bryozoans. 31,32 Interestingly, shell tubules in bivalves are formed secondarily through caecal protrusions from the mantle epithelium that dissolve pre-existing shell layers, while the growth of shell tubules in gastropods is more similar to that of brachiopod punctae, which are formed primarily during shell production. ...
... 50,51 By contrast, shell tubules appeared to be more prominent and well-developed in early Cambrian molluskan species than their modern representatives. 30 The high density of tubules may partly serve as a compensation mechanism for the inherent weaknesses of initially mineralized shells, adding complexity to the process of shell calcification in early Cambrian mollusks. Together, the mechanical supports and anti-microboring functions of the tubule system contribute significantly to the structural integrity of shells and the ecological adaptability of skeletonized mollusks in early Cambrian seas. ...
The evolutionary mechanism behind the early Cambrian animal skeletonization was a complex and multifaceted process involving environmental, ecological, and biological factors. Predation pressure, oxygenation, and seawater chemistry change have frequently been proposed as the main drivers of this biological innovation, yet the selection pressures from microorganisms have been largely overlooked. Here we present evidence that calcareous shells of the earliest mollusks from the basal Cambrian (Fortunian Age, ca. 539–529 million years ago) of Mongolia developed advanced tubule systems that evolved primarily as a defensive strategy against extensive microbial attacks within a microbe-dominated marine ecosystem. These high-density tubules, comprising approximately 35% of shell volume, enable nascent mineralized mollusks to cope with increasing microbial bioerosion caused by boring endolithic cyanobacteria, and hence represent an innovation in shell calcification. Our finding demonstrates that enhanced microboring pressures played a significant role in shaping the calcification of the earliest mineralized mollusks during the Cambrian Explosion.
... Specialized cellular extensions, known as caeca, are present in the delicate shell tubules of various mollusk lineages, e.g., extant bivalves, gastropods, polyplacophorans (chitons), 28 and Cambrian helcionelloid mollusks. 29,30 Similar structures, called punctae, are also a characteristic feature of the calcareous skeletons of brachiopods and bryozoans. 31,32 Interestingly, shell tubules in bivalves are formed secondarily through caecal protrusions from the mantle epithelium that dissolve pre-existing shell layers, while the growth of shell tubules in gastropods is more similar to that of brachiopod punctae, which are formed primarily during shell production. ...
... 50,51 By contrast, shell tubules appeared to be more prominent and well-developed in early Cambrian molluskan species than their modern representatives. 30 The high density of tubules may partly serve as a compensation mechanism for the inherent weaknesses of initially mineralized shells, adding complexity to the process of shell calcification in early Cambrian mollusks. Together, the mechanical supports and anti-microboring functions of the tubule system contribute significantly to the structural integrity of shells and the ecological adaptability of skeletonized mollusks in early Cambrian seas. ...
... They may be distributed randomly or follow a comarginal pattern associated with rugae ( Fig. 14H). Vendrasco et al. (2011) considered that the pores extended through much or all of the shell wall and noted that similar structures had been described by Kouchinsky (2000a), Parkhaev (2006) and Feng & Sun (2006) in a variety of Cambrian helcionelloids. While some pores opened to the shell exterior, others appear to have been connected with the organic components of the shell structure and periostracum. ...
... Such structures are rarely visible in available material, where the surface is often very finely papillate. Vendrasco et al. (2011) summarized observations by Kouchinsky (2000a), Parkhaev (2006) and Feng & Sun (2006) concerning tubercles rising perpendicular from the surface of the internal moulds in helcionelloids that were interpreted as pores entering into, or passing through, the shell. Comparable tubercles are widely and variably distributed in specimens of Mellopegma schizocheras from GGU sample 271492. ...
Diverse assemblages of helcionelloid molluscs and mollusc-like microfossils are described from the upper Henson Gletscher Formation (Cambrian, Miaolingian Series, Wuliuan Stage) of Lauge Koch Land and western Peary Land, North Greenland (Laurentia). The fauna compares closely to an assemblage of similar age from the Coonigan Formation of Australia, although the latter is preserved as silica replicas while the North Greenland fossils are dominantly preserved as phosphatized internal moulds. These internal moulds often retain a detailed impression of the inner surface of the shell, with a fine pitted texture typically present. Prominent deep grooves on the sub-apical surface in the erect helcionellids Dorispira and Erugoconus, corresponding to ridges on the shell interior, seem to be associated with control of water flow through the mantle cavity. Well-developed shell pores, preserved as tubercles on the internal mould, are common in species of the laterally compressed Mellopegma. New taxa: Dorispira avannga sp. nov., Dorispira septentrionalis sp. nov., Dorispira tavsenensis sp. nov., Dorispira tippik sp. nov., Erugoconus acuminatus gen. et sp. nov., Scenella? siku sp. nov., Sermeqiconus gen. nov., Tavseniconus erectus gen. et sp. nov., Vendrascospira troelseni gen. et sp. nov., Vendrascospira frykmani gen. et sp. nov.
... Cambrian and earliest Ordovician strata have yielded numerous univalves referred to the Class Helcionelloida by Peel (1991aPeel ( , 1991b, which is approximately equivalent in composition to the Order Helcionelliformes (within gastropod Subclass Archaeobranchia) of Parkhaev (2019) and earlier papers cited therein (see discussion by Geyer 1994 andKouchinsky 2022). However, the resemblance of their bilaterally symmetrical shells, which are generally coiled through a quarter of a whorl or more, to patellids is superficial and a variety of structures on the shell interior in Helcionelloida are seemingly unique to the group (Peel 1991a(Peel , 1991bKouchinsky 2000;Parkhaev 2000Parkhaev , 2002Parkhaev , 2006Vendrasco et al. 2010Vendrasco et al. , 2011Peel & Kouchinsky 2022). Late Cambrian to early Ordovician Hypseloconida were placed within Class Tergomya by Peel (1991a) and Yochelson & Webers (2006), but a provocative submission by Dzik (2010) argued that similarities in muscle scars patterns with the bivalved Angarella Asatkin, 1932 suggested brachiopod affinities. ...
... The system of tubules in Cupitheca is likewise similar to what occurs in many molluscs. Particularly striking are the similarities with Cambrian helcionelloids, including relatively dense vertical (orthogonal to shell surface) canals that occur without branching throughout most or all of the shell thickness (Parkhaev, 2006;Feng & Sun, 2006;Vendrasco et al., 2011b). The coiled early Cambrian molluscs Barskovia and Philoxenella show a tubule pattern (Kouchinsky et al., in press) the same as that of Cupitheca. ...
Cupitheca is an enigmatic tubular fossil common in early Cambrian deposits worldwide. It has recently been argued to be a hyolith, probably orthothecid. Cupitheca had a dense network of mantle-filled tubules that connected to what we interpret as a continuous organic periostracum. The innermost shell layer consists of horizontal or slightly inclined bundles of fibres elongated along the a-axis and offset from other bundles at aragonitic twin angles, confirming aragonite as the original mineralogy for the shell of Cupitheca. This is a similar Shell microstructure to that inferred for Cambrian hyoliths, strengthening the claim that Cupitheca is a hyolith. This shell microstructure of bundled aragonite fibres and the tubule systems can also be seen in many Cambrian molluscs and other lophotrochozoans. In some lineages this shell texture evolved into fracture-resistant crossed lamellar microstructure and in others nacre. These transitions began to occur sometime between the mid-Cambrian and Ordovician, and nacre and crossed lamellar microstructure were the most common constituents of the inner shell layer of molluscs by the middle or late Palaeozoic Era.
... Works describing Cambrian mollusks of Australia have been published by researchers from all over the world: (Berg-Madsen and Peel, 1978;Hinz-Schallreuter, 1997;Kruse, 1990Kruse, , 1991Kruse, , 1998Kruse et al., 2004;Parkhaev, 1998Parkhaev, , 2004aParkhaev, , 2006Parkhaev, , 2013Parkhaev, , 2017aVendrasco et al., 2010Vendrasco et al., , 2011. Recently, these studies of Cambrian mollusks of Australia have been continued by Australian scientists (Brock, 1998;Brock and Cooper, 1993;Brock and Paterson, 2004;Jacquet et al., 2014Jacquet et al., , 2017Topper et al., 2009). ...
The Cambrian malacofauna of Australia is taxonomically among the most diverse of synchronous faunas. In the number of described mollusk species, it rivals the Siberian and Chinese faunas. To date, 80 valid species and 12 species in open nomenclature, apparently representing new undescribed taxa, have been recorded from the Lower–Middle Cambrian successions of Australia. In addition, six species names can be considered as junior synonyms. The ranges of distribution of mollusk species plotted over the modern stratigraphic scheme reveal four major molluskan evolutionary assemblages in the Tommotian–Undillan interval. In a paleogeographical context, the Cambrian malacofauna of Australia has 29 species in common with the Siberian Platform, Kazakhstan, Altai-Sayan, Transbaikalia, Mongolia, North and South China, Morocco, Antarctica, Europe (Denmark, Germany), Greenland, North America, and New Zealand, providing important correlation links between these regional stratigraphic schemes.
... A stem group rather than crown group position for helcionelloids is further supported by the presence of paired bristle-like clusters extending from the aperture of the Pelagiella shell which have a striking resemblance to the parapodial chaetae of some polychaetes 60 . Additionally, helcionelloids are characterized by a different muscle system, densely porous shells that are more common in brachiopods than molluscs, and calcitic semi-nacre microstructures which are more typical of lophophorates [61][62][63] . These observations suggest that the Helcionelloida were stem-group molluscs that retained a number of shared basal features with lophotrochozoan ancestors. ...
The dynamics of how metazoan phyla appeared and evolved – known as the Cambrian Explosion – remains elusive. We present a quantitative analysis of the temporal distribution (based on occurrence data of fossil species sampled in each time interval) of lophotrochozoan skeletal species (n = 430) from the terminal Ediacaran to Cambrian Stage 5 (~545 – ~505 Million years ago (Ma)) of the Siberian Platform, Russia. We use morphological traits to distinguish between stem and crown groups. Possible skeletal stem group lophophorates, brachiopods, and molluscs (n = 354) appear in the terminal Ediacaran (~542 Ma) and diversify during the early Cambrian Terreneuvian and again in Stage 2, but were devastated during the early Cambrian Stage 4 Sinsk extinction event (~513 Ma) never to recover previous diversity. Inferred crown group brachiopod and mollusc species (n = 76) do not appear until the Fortunian, ~537 Ma, radiate in the early Cambrian Stage 3 (~522 Ma), and with minimal loss of diversity at the Sinsk Event, continued to diversify into the Ordovician. The Sinsk Event also removed other probable stem groups, such as archaeocyath sponges. Notably, this diversification starts before, and extends across the Ediacaran/Cambrian boundary and the Basal Cambrian Carbon Isotope Excursion (BACE) interval (~541 to ~540 Ma), ascribed to a possible global perturbation of the carbon cycle. We therefore propose two phases of the Cambrian Explosion separated by the Sinsk extinction event, the first dominated by stem groups of phyla from the late Ediacaran, ~542 Ma, to early Cambrian stage 4, ~513 Ma, and the second marked by radiating bilaterian crown group species of phyla from ~513 Ma and extending to the Ordovician Radiation.
... The system of tubules in Cupitheca is likewise similar to what occurs in many molluscs. Particularly striking are the similarities with Cambrian helcionelloids, including relatively dense vertical (orthogonal to shell surface) canals that occur without branching throughout most or all of the shell thickness (Parkhaev, 2006;Feng & Sun, 2006;Vendrasco et al., 2011b). The coiled early Cambrian molluscs Barskovia and Philoxenella show a tubule pattern (Kouchinsky et al., in press) the same as that of Cupitheca. ...
A study on the morphological characteristics of helcionelloids and its microstructure from the Nanjiang area (north Sichuan, China) at the northern Yangtze Platform is taken to understand its position in the phylogeny. Helcionelloids fossils from the Kuanchuanpu Formation of the Changtanhe–Maolinzi section include 7 genera and 11 species. There are distinct differences on the degree of shell bending, the apical morphology and apex position, the outline of the apeture, and the height of the shell, which constitute an important identification feature. Though the helcionelloid apices have varying degrees of rotation towards the aperture, they have no any evident distortion. A pair of basally symmetrical muscle scars are discovered on the shells of helcionelloids (such as Bemella simplex ), showing distinct difference comparing with those of the stem‐group gastropod (e.g., Pelagiella ). The prismatic shell layer of helcionelloids has been observed, which are common components in Cambrian molluscs. They are significantly different from the dense layer microstructure found in contemporary molluscs. The microstructures, muscle scars and morphological characteristics demonstrate that the helcionelloid is a stem‐group of molluscs.
The hyolith fauna of the middle Bystraya Formation (Cambrian Series 2) of eastern Transbaikalia (Zabaykalsky Krai), Siberia, includes at least 17 described taxa distributed between the orders Hyolithida and Orthothecida. Species of Microcornus, Parkula, Conotheca, Neogloborilus and Cupitheca are widely reported from Cambrian strata elsewhere. Triplicatella uslonica sp. nov. is known only from Transbaikalia. Dauritheca is proposed as a replacement generic name for the junior homonym Pachytheca, originally described from Xinjiang, China, and its range is extended to Transbaikalia. A conch with prominent comarginal ribs is referred to Salanytheca daurica sp. nov., a genus otherwise known from the early Cambrian of Mongolia and northern Siberia.
John S. Peel [john.peel@pal.uu.se], Department of Earth Sciences (Palaeobiology), Uppsala University, Uppsala, Sweden; Alexander P. Gubanov [Alexander.Gubanov@pal.uu.se], Museum of Evolution, Uppsala University, Uppsala, Sweden.
A section is described, which includes the upper part of the Vendian, Lower Cambrian, and lower Middle Cambrian strata. The section is situated on the right bank of the Yenisei River about 5 km downstream from Plakhinsky Island. It has been established that the rocks in the section under study differ signifficantly in lithology from the formations (Izluchina, Sukharikha, Krasny Porog, and Shumny) of the Igarka district typical of this age interval. It is confirmed that a break exists between the Early and Middle Cambrian, which covers the greatest part of the Botomian Age (except the lower part of the Calodiscus-Erbiella Zone) and extends to the Anopolenus henrici-Corynexochus perforatus Zone of Middle Cambrian Mayaian Age. Abundant remains of the Cambrian fauna have been found and identified: small-shell organisms, trilobites, algae, brachiopods, and gastropods. For the first time this section has been characterized to a sufficient degree. The boundary between the Vendian and Cambrian strata has been drawn, and the entire range of deposits to the Upper Cambrian strata has been stratified.
The shell valve surfaces of the chitons Ischnochiton (lschnoradsia) australis, Crypt oplax mystka, Liohphura (Liolophura) gaimardi and Omthochiton quercinus are studied by scanning electron microscopy. The distribution of aesthete caps is examined in relation to dorsal sculpturing, and the formation of these complexes is compared with the arrangement of holes which penetrate the ventral surface and eave tissue. The presence of specialized aesthetes (ocelli) on Uolophura (L.)gaimardi and O. quercinus is described. The use of aesthete densities as taxonomic indicators, and possible functions in relation to species specific environmental conditions are discussed.
The phytogeny and evolutionary history of the strep-toneuran Gastropoda is reconsidered in the light of (i) recent discoveries of different types of organization, (ii) new data sets based on modern techniques, and (iii) the dado-evolutionary method to trace genealogical relationships. The phylogcnctic analysis by means of traditional (homology-analogy) and cladistic (apomorphy-plesiomorphy) character analysis reveals several conclusions:
(1) The Gastropoda originated by torsion from monoplacophoran ancestors after the Cephalopoda split off. Torsion itself is understood as a two-step process, resulting in advantages for the larvae (presence of operculum) and for the adults (anterior mantle cavity). All Gastropoda form a holophyletic group
(2) The proposed gastropod archetype differs Largely from previous suggestions in being more similar to docoglossate gastropocls than to zeugobranchs
(3) The Docoglossa are regarded as the earliest gastropod offshoot, having retained ancestral (atereoglossate) radula conditions
(4) Based on various lines of evidence the ‘symmetrical’ limpet groups (Docoglossa, including hotvent group-C?, Cocculiniformia), primary without helicoid coiling of teteoconch, are accepted as primithe for the Gastropoda
(5) CocculinifOrmia, Neritimorpha and possibly hot-vent group-A represent distinct archaeogastropod radiations
(6) The Vetigastropoda, originally including zeugobranchs and trochoids are a hotophyletic group and include also the Lepetodriloidea (= hot-vent group-B). In contrast, the Neomphaloidea and Seguen zioidea represent distinct Lines of evolution
(7) According to their hypoathroid or dystenoid nervous system the architaenioglossate groups are included in the *Archaeogastropoda* which are defined as an orthophyletic grade
(8) A major evolutionary gap (a large inaease in size enabled ptanktotrophic larvae; epiathroid nervous system) separates the higher streptoneurans (= *Apogastropoda*) from the *Archaeogastropoda*. The Loxonematoidea are regarded as the common stem group of Caenogastropoda as well as of the ectobranch—allogastropod—euthyneuran line (Heterobranchia)
(9) The Caenogastropoda are a holophyletic group, of which the Centhioidea represent the basic stock. The Stenoglossa (= Neogastropoda) probably origined from *Neotaenioglossa* sharing distinct simitanSies in sperm-morphology
(10) Canpani1e symbolicum Iredale, 1917 (Campanhimorpha) is a probable representative of the first group that made a distinct step towards the euthyneuran organization
(11). Valvatoidea (Ectobranchia) form a separate offshoot outside the Caenogastropoda. They appear as an independent side-branch at the base of the allogastropod grade
(12) The *Allogastropoda*, a grade, include the fossil Nerineoidea and at least four recent lines (Architectonicoidea & Omalogyridae; Rissoelloidea; Glacidorboidea; Pyramidelloidea) which represent a step by step evolution towards the euthyneuran level of organization
(13) Euthyneura are monophyletic. However, the status of the Opisthobranchia (bob- or paraphyletic) is still ambiguous. The Pulmonata (including the Gymnomorpha) represent a holophyletic assemblage and the own group of Gastropoda
(14) The respective phylogram (Fig. 5) is transformed in a classification by the use of the so-called clado-evotutionary method which enables an unequivocal retransformation and expresses the different degrees of likelihood (correlated with the main evolutionary gaps) in the proposed phylogenetic pathway of the streptoneurous Gastropoda
