Shell structure,ornamentation and affinity of the problematic early Cambrian brachiopod Heliomedusa orienta

The origin of the Brachiopoda has long been a hotly debated topic, and various models have been proposed following the latest finds of exceptionally preserved material. The lower Cambrian (Stage 3) Heliomedusa orienta from the Chengjiang Konservat-Lagerstätte, eastern Yunnan of South China, is an important example of exceptional preservation. A wide variety of affinities have been proposed for Heliomedusa, but recently it has been suggested to reside within the mickwitziids, which may form a stem group to the Brachiopoda. Detailed studies of exceptionally preserved Heliomedusa have increased our knowledge of the soft-part anatomy of this important early brachiopod, but unfortunately, almost nothing is known about its shell structure. Here, we describe new exceptionally preserved specimens from the Chengjiang biota to better reveal both shell structure and ornamentation. Its reticulate–pustulose ornament and tubular structure are reminiscent of traits seen in other mickwitziid brachiopods. In addition, two types of setae can be observed. Apart from the pyritized marginal mantle setae, some tubules are filled with iron oxides, potentially representing thinner and shorter penetrative setae. Both valves of H. orienta appear to have been less mineralized as compared to Mickwitzia monilifera, and the two species differ in diameter and density of tubules and pustules, and in terms of slightly less projected profile of ventral valve with lower umbo posteromedially placed. Although Heliomedusa clearly is closely related to Mickwitzia, their different preservational modes (compacted poorly mineralized/noncompacted mineralized) make detailed comparison difficult; they are provisionally kept as separate genera pending further studies of better-preserved Chinese material.     

Protegulum and brephic shell of the earliest organophosphatic brachiopods

Early development stages imprinted on the shells of Cambrian brachiopods from the class Linguliformea (orders Paterinida, Lingulida, Acrotretida) were studied with scanning electron microscope based on a large collection from the Siberian Platform. Some specimens of all three orders preserved protegulum (embryonic shell); their brephic (juvenile) shells, also were studied. Many of them might lack larval development stage as it is known for the recent representatives of the family Lingulidae. But unlike recent lingulids, the surface of the juvenile dorsal valves of all studied linguliformeans bore two (rarely three) pairs of gentle elevations accommodating bundles of setae, which sometime preserve as groups of fine imprints along their margins. Recent Lingula and Glottidia lack setae in this stage. On the other hand, recent classes Craniformea and Rhynchonelliformea have setae, but they develop in the larval stage. Most of brachiopod groups have the setae in the adult stage but these setae have different origin, are short, located on the lateral and anterior ends of the shell, and grow from the marginal cells of the mantle.     

RHYNCHONELLIFORMEAN BRACHIOPODS WITH SOFT-TISSUE PRESERVATION FROM THE EARLY CAMBRIAN CHENGJIANG LAGERSTÄTTE OF SOUTH CHINA

Abstract:  Cosmopolitan kutorginates, the most abundant Early Cambrian rhynchonelliformean brachiopods, became extinct at the end of the Middle Cambrian. Consequently, any information concerning the anatomy of this peculiar lineage of brachiopods has great phylogenetic significance with regard to their extant relatives for analogies with the stem-group clade. Such data have been supplied from fossils of which the soft parts have been preserved in exceptional detail. A new brachiopod, Kutorgina chengjiangensis sp. nov., from the Early Cambrian Chengjiang Lagerstätte of southern China, is described here. It is the first articulated brachiopod species collected from this deposit. The specimens preserve a set of soft-body parts, i.e. lophophore, digestive tract and pedicle, all previously poorly known in almost all Palaeozoic calcareous brachiopod taxa. The lophophore attains an early spirolophe stage, clearly homologous to that in the coeval lingulids. The digestive tract consists of a mouth, oesophagus, swollen stomach, intestine and a terminal anus. The pedicle protruding between the valves is stout and elongate, with annulated lamellae on the surface, and contains a putative cœlomic cavity. K. chengjiangensis displays the characteristics of the stem group of calcareous brachiopods, and illustrates anatomical similarities between Cambrian phosphatic- and calcareous-shelled brachiopods, thus corroborating that the Brachiopoda are a monophyletic group.     

EARLY CAMBRIAN BRACHIOPODS FROM NORTH-EAST GREENLAND

Abstract:  A diverse assemblage of late Early Cambrian brachiopods is described from the Bastion and Ella Island formations of North-East Greenland. The fauna includes nine species, representing all three extant brachiopod subphyla in addition to the stem group brachiopod Mickwitzia cf. occidens . Four linguliforms: Eoobolus priscus , Botsfordia caelata , Micromitra bella , Vandalotreta sp., three rynchonelliforms: Obolella crassa , Kutorgina reticulata , and an unidentified chileid plus a possible craniiform species occur. The fauna shows similarities to late Early Cambrian (Dyeran Stage) brachiopod faunas of eastern Canada and the United States, but also to faunas from the late Early Cambrian (Botomian–Toyonian equivalent) of Australia, Antarctica and Siberia.     

The exceptionally preserved Early Cambrian stem rhynchonelliform brachiopod Longtancunella and its implications

Zhang, Z., Holmer, L. E., Ou, Q., Han, J. & Shu, D. 2011: The exceptionally preserved Early Cambrian stem rhynchonelliform brachiopod Longtancunella and its implications. Lethaia, Vol. 44, pp. 490–495. The extraordinary Longtancunella chengjiangensis is one of the rarest and most problematic brachiopods from the Early Cambrian Chengjiang Lagerstätte, where it occurs in unique gregarious clusters with up to ten individuals attached by their stout pedicles to a single hard exoskeleton. Although the general morphology and soft anatomy of Longtancunella is available, its taxonomy and systematic placement within the Brachiopoda remains problematic. New exceptionally preserved specimens show that the pedicle of Longtancunella cannot be considered homologous with the pedicles in crown Rhynchonelliformea or Linguliformea. The pedicle of Longtancunella emerges from a ventral umbonal foramen with a rounded plate that must have been secreted by specialized ventral mantle epithelium. The rounded plate is proposed to be a homologue to the colleplax – a plate covering the umbonal foramen, which is otherwise known from the extinct rhynchonelliform chileates. Longtancunella is proposed to represent a soft‐shelled stem rhynchonelliform brachiopod with chileate features, thus demonstrating for the first time that the chileate‐like umbonal perforation functions as a pedicle opening. The unusual preservation of the annulated chileate‐like holdfast supports the view that it may have been secreted as stacks of chitinous or even mineralized ‘attachment pads’. Together with having a spirolophous lophophore and U‐shaped gut, Longtancunella displays a unique mixture of linguliform and rhynchonelliform characters that throw new light on an early stage of rhynchonelliform diversification. □Brachiopods, Cambrian, Chengjiang Lagerstätte, Chileata, colleplax, pedicle.     

Origin and dispersal of the earliest brachiopods

Brachiopods first appeared at the very beginning of the Phanerozoic together with the first skeletal organisms. Most brachiopod taxa that arose in the first half of the Cambrian had a short temporal range and became completely extinct by the middle of the Middle Cambrian. Rigid articulation of the valves of brachiopods was provided by various structures, which also appeared in the Early Cambrian. This fact points to the importance of this feature for the formation of the whole group and at the same time testifies to the high variability of rigid articulation at the early stages of brachiopod evolution. This is a typical manifestation of archaic diversity in this animal phylum, which appeared very early in the Phanerozoic. Another important property of the archaic diversity of the early brachiopods was the large number of centers of diversification. As for the majority of groups, climatic zonality was the main factor determining the distribution of brachiopods at the beginning of the Phanerozoic. The main ecological types of brachiopods also appeared in the Early Cambrian.     

First report of Schizopholis (Lingulata,Brachiopoda) from the Tsinghsutung Formation (Cambrian Series 2, Stage 4) in Guizhou,China

Schizopholis Waagen, 1885 is a genus of linguliform brachiopod, which is known from Cambrian Stage 4 to the Wuliuan Stage of Australia, Antarctica, Pakistan and China. Recently, new material of Schizopholis was discovered from the upper part of the Tsinghsutung Formation (Cambrian Series 2, Stage 4) near Balang village, Jianhe County, Guizhou Province, China. These specimens display the oval pedicle opening in the ventral valve, a median tongue and a pair of tubercles in the dorsal valve that are characteristic features of Schizopholis napuru (Kruse, 1990). This is the first time that this species has been described from Guizhou Province, China. Previously, fossils of this species are usually preserved in carbonate deposits, but the new material documented herein preserved in mudstone of the Tsinghsutung Formation, providing new information regarding both the paleogeographic distribution and paleoecology of this species.     

A Stem Group Brachiopod From The Lower Cambrian: Support For A Micrina (Halkieriid) Ancestry

The shell structure of the Lower Cambrian Mickwitzia , a bilaterally symmetrical bivalve hitherto doubtfully assigned to the Brachiopoda, confirms that the genus shares characters with linguliform brachiopods. The columnar lamination of its organophosphatic shell is homologous with that characterizing acrotretides. The shell, however, is also pervaded by striated apatitic tubes indistinguishable from those permeating the sclerites of the problematic organophosphatic, laminar–shelled Micrina which is close to Halkieria . No crown group brachiopods have such tubes that are presumed to have contained setae. The presence of both these features in the Mickwitzia shell suggests that the stock is a stem group brachiopod with a halkieriid ancestry.     

The brachiopod <Emphasis Type="Italic">Eoobolus</Emphasis> from the Early Cambrian Mural Formation (Canadian Rocky Mountains)

The Early Cambrian brachiopod, Eoobolus, is one of the first representatives of the superfamily, Linguloidea, the defining characteristics of which include the classical morphology of oval shells and a pedicle that emerges from between the two valves. The material described here from the Mural Formation (Jasper National Park, Canadian Rocky Mountains) provides well-preserved muscle scars and larval shells that allow a discussion of the muscle system and the larval morphology of Eoobolus. The dorsal larval shell exhibits a morphology similar to other Cambrian linguloids, but also to paterinids, Mickwitzia muralensis, and some rhynchonelliforms. This suggests that there was a lesser degree of disparity among brachiopod larvae in the Cambrian than there is today. The muscle system of Eoobolus is similar to other linguloids, but differs from that of Recent lingulids and discinids by having one or two more pairs of oblique muscles. New data on the distribution of features characteristic of the family Eoobolidae question the validity of this family.     

A spinose stem group brachiopod with pedicle from the Middle Cambrian Burgess Shale

A new genus and species of a Middle Cambrian stem group brachiopod, Acanthotretella spinosa n. gen. and n. sp., is described from the Burgess Shale Formation. Most of the 42 specimens studied came from the Greater Phyllopod bed (Walcott Quarry) and were collected from five bed assemblages, each representing a single obrution event. Specimens are probably preserved within their original habitat. In contrast to all brachiopods known from the Burgess Shale, the shells of the new stem group brachiopod are often deformed and do not show signs of brittle breakage, which suggests that the valves were originally either entirely organic in composition or, more likely, had just a minor mineral component. Acanthotretella spinosa differs from all the other described Cambrian brachiopods in that it is covered by long, slender and possibly partly mineralized spines that are posteriorly inclined at an oblique angle away from the anterior margin. The spines penetrate the shell and are mainly comparable with the thorn‐like organic objects that have been inferred from early siphonotretoid brachiopods. The pedicle was slender and was composed of a central coelomic region and emerged from an apical foramen at the end of an internal pedicle tube. The finding of a pedicle attached to the macrobenthic algae Dictyophycus and other epibenthos implies that A. spinosa did not have an infaunal mode of life. The visceral region and interior characters are poorly preserved.     

CAMBRIAN PALAEONTOLOGY OF FENNOSCANDIAN BASEMENT FISSURES

Fossils from two ecologically and palaeogeographically interesting Cambrian outliers in the Precambrian basement of Fennoscandia are described or discussed. One of the localities is a fissure system, filled with sandstone, at Långbergsöda-Öjen in Saltvik, Province of Aland, Finland. The occurrence of the brachiopod Ceratreta tanneri (Metzger 1922) indicates a Late Cambrian age rather than Early Cambrian as assumed hitherto. The other locality, about 1.5 km W of the Fortress of Bohus, at Kungälv, Province of Bohuslän, Sweden, consists of a fissure and a trench-like crevice bounded by joints, containing a sequence of calcareous sedimentary breccia, grey limestone with coarse sand, and a late Medial Cambrian fauna. The sequence continues with black shale and bituminous dark limestone, containing large fragments of older igneous and sedimentary rocks as well as a Late Cambrian fauna.     

THE ENIGMATIC EARLY CAMBRIAN SALANYGOLINA– A STEM GROUP OF RHYNCHONELLIFORM CHILEATE BRACHIOPODS?

Abstract:  New material of the enigmatic brachiopod Salanygolina obliqua Ushatinskaya from the Early Cambrian of Mongolia shows that it has a colleplax – a triangular plate – in the umbonal perforation, which is enlarged by resorption. This structure is otherwise only known from the equally enigmatic Palaeozoic orders Chileida and Dictyonellida (Rhynchonelliformea, Chileata). The colleplax in Salanygolina is here considered to be homologous with that of the chileates. Salanygolina is also provided with a ridge-like pseudodeltidium, which is another chileate feature. Other characters of Salanygolina , like the radial arrangement of adductor muscle scars and postero-medially placed internal oblique muscles are characteristic of chileates, but also found in the paterinates. In contrast, mixoperipheral dorsal valves with low rudimentary interareas are well known in paterinates, but not yet recorded from chileates. Thus, Salanygolina shows a mosaic combination of morphologic characters, known both from the paterinates and chileates, indicating that it may represent a stem group of the rhynchonelliform chileate brachiopods. The laminar phosphatic secondary shell of Salanygolina is composed of closely packed and nearly identical hexagonal prisms, oriented with their long axis normal to the laminae in a honeycomb pattern. The prism walls appear to have originally been composed of organic membranes and might represent precursors of the organic sheaths of calcite fibers that are typical of calcitic shells with a fibrous microstructure.     

辽东寒武纪三叶虫Redlichia (Pteroredlichia) murakamii Resser et Endo的蜕壳

华北辽东本溪寒武纪三叶虫Redlichia(Pteroredlichia)murakamii蜕壳标本完好地保存了头盖向下翻转的蜕壳状态,为寒武纪Redlichia的蜕壳模式提供了新的视角。此标本自由颊未保留,胸尾相连,头盖与胸部分离,头盖向下翻转,基本保持原位,为原地埋藏的蜕壳标本。蜕壳过程如下:面线裂开,头盖耸起卷曲并翻转,与胸部分离,胸部扭动,虫体摆脱老壳向前爬出。此蜕壳方式在McNamara(1986)报道的澳大利亚寒武纪Redlichia的蜕壳类型中并未出现。     

Architecture and function of the lophophore in the problematic brachiopod Heliomedusa orienta (Early Cambrian, South China)

The detailed structure of the lophophore is a key diagnostic character in the definition of higher brachiopod taxa. The problematic Heliomedusa orienta Sun and Hou, from the Lower Cambrian Chengjiang Lagerstätte of Yunnan, southwestern China, has a well-preserved lophophore, which is unlike that of any known extant or extinct brachiopods. Based on a comparative study of lophophore disposition in H. orienta and the extant discinid Pelagodiscus atlanticus, the in- and excurrent pattern and shell orientation of H. orienta are described and discussed. Reconstructions of lophophore shape and function are based on numerous specimens and comparison with P. atlanticus. The lophophore is composed of a pair of lophophoral arms that freely arch posteriorly rather than coiling anteriorly as commonly seen in fossil and recent lingulids. The lophophore is attached to the dorsal lobe of the mantle; it has neither calcareous nor chitinous supporting structures, and is disposed symmetrically on either side of the valve midline. The mouth can be inferred to be located at the base of the two brachial tubes, slightly posterior to the anterodorsal projection of the body wall. The lophophoral arms bear laterofrontal tentacles with a double row of cilia along their lateral edge, as in extant lingulid brachiopods. The main brachial axes are also ciliated, which presumably facilitated transport of mucous-bound nutrient particles to the mouth. The unique organization of the lophophore in Heliomedusa is not like any known fossil and living brachiopods. This clearly demonstrates that H. orienta is not a member of any crown group. It is here considered as a member of the brachiopod stem group, which challenges recent interpretations of a close discinid affinity.     

Plywood‐like shell microstructures in hyoliths from the middle Cambrian (Drumian) Gowers Formation,Georgina Basin,Australia

Hyoliths are a group of Palaeozoic fossils with calcareous shells whose affinities remain controversial. As their shells were originally aragonitic, their fossils are usually coarsely recrystallized, and few data on their microstructure are available. We report hyoliths from the middle Cambrian (Drumian, Floran) Gowers Formation of the eastern Georgina Basin, Queensland. These are preserved as phosphatic internal moulds, often with the inner layers of the shell also partly replaced by phosphate. Microstructural details preserved by this early diagenetic phosphatization show that these hyolith conchs were originally composed of fibrous crystallites, c. 0.5 μm wide, parallel to one another and to the inner surface of the shell. In several species, the fibres are arranged in a plywood‐like structure composed of multiple lamellae with a different fibre orientation in each lamella: often they are transversely oriented (relative to the long axis of the conch) in the inner part of the wall and longitudinally oriented in the outer part. Opercula also show a microstructure of parallel fibres. The lamello‐fibrillar microstructure we report from hyoliths is reminiscent of microstructures of many Cambrian molluscs; that this microstructure is found in both conchs and opercula suggests that these structures are serial homologues of one another, and in this respect they resemble brachiopod valves. As with many other biological plywoods, the hyolith shell probably records self‐organization in a liquid‐crystal‐like organic matrix. This provided a straightforward way to construct a material that could resist stresses from different directions, offering an effective defence against predators.     

Tommotiids from the early Cambrian (Series 2, Stage 3) of Morocco and the evolution of the tannuolinid scleritome and setigerous shell structures in stem group brachiopods

An assemblage of tannuolinid sclerites is described from the Amouslek Formation (Souss Basin) of the Anti‐Atlas Mountains in Morocco. The assemblage contains two species, Tannuolina maroccana n. sp., which is represented by a small number of mitral and sellate sclerites, and Micrina sp., represented by a single mitral sclerite. Tannuolina maroccana differs from other species of the genus in the presence of both bilaterally symmetrical and strongly asymmetrical sellate sclerites. This observation suggests that the scleritome of Tannuolina was more complex than previously thought and that this tommotiid may have held a more basal position in the brachiopod stem group than previously assumed. The shell structure of both T. maroccana and Micrina sp. is well preserved and exhibits two fundamentally different sets of tubular structures, only one of which was likely to contain shell‐penetrating setae. Based on these observations, the structure of the tannuolinid shell is discussed and its implications for the evolution of tubular microstructures in stem and crown group brachiopods are analysed.     

An early Ordovician patelliform gastropod, Palaelophacmaea, reinterpreted as a coelenterate

Yochelson, Ellis L. & Stanley, George D., Jr. 1981 12 15: An early Ordovician patelliform gastropod, Palaelophacmaea , reinterpreted as a coelenterate. Lethaia , Vol. 15, pp. 323–330. Oslo. ISSN W24–1164.
The fossil Palaelophacmaea criola Donaldson, from the early Ordovician Stonehenge Formation of central Pennsylvania, was described as a patelliform gastropod. A reinterpretation of the type lot and study of a few additional specimens provide the basis for an alternative placement. Palaelophacmaea is here assigned to the Hydrozoa, as a possible chondrophore. It has an exceptionally thin shell or test and concentric but irregular corrugations. Cambrian univalve genera having a more or less circular outline that are currently assigned to the Gastropoda or Monoplacophora should be reexamined to see whether they have the features of fossil chondrophore coelenterates rather than those of molluscs. The late Cambrian Palaeoacmaea Hall & Whitfield is removed from the monoplacophoran Mollusca and left unassigned as to phylum. We judge that at least some early Cambrian species of Scenella are probably coelenterate remains. * Early Ordovician , Palaelophacmaea, Gastropoda, Monoplacophora, Hydrozoa .     

Ultrastructural Similarities Between Setae of Brachiopods and Polychaetes1

Larvae of the brachiopod Terebratalia transversa Sowerby have 2 bundles of setae on each side of their mantle lobe. Each seta grows out of a follicle of epidermal cells. The cisternae and associated vesicles of the Golgi bodies in lateral follicular cells are filled with electron dense material. The basal follicular cell, or chaetoblast, has apical microvilli projecting into the basal ends of the longitudinal channels of the seta. The channel partitions are composed of fine fibers oriented parallel to the setal axis. The close structural and developmental similarities between polychaete and brachiopod setae are discussed.