Craniid Brachiopods Research Articles

Syn vivo encrustation of Porambonites Pander, 1830 (Brachiopoda) by craniid brachiopods in the Late Ordovician of Estonia

Two new brachiopod–brachiopod symbiotic overgrowths have been discovered from the Kukruse Regional Stage (Sandbian, Ordovician) of Estonia. Both the Philhedra rivulosa–Porambonites sp. and the Petrocrania sp.–Porambonites sp. overgrowths were beneficial to the encrusting craniid and might have been slightly harmful to the host brachiopod. The craniids could have been facultative kleptoparasites. Our data show that craniids significantly preferred the smooth shells of Porambonites sp. over the coarsely ribbed shells of Platystrophia sp. and the moderately ribbed shells of Cyrtonotella sp. and Glossorthis sp. This suggests that, at least against craniids, having strong ribs could have been a successful antifouling strategy.

Invertebrate epibionts on Ordovician conulariids from the Prague Basin (Czech Republic, Bohemia)

Approximately 4% of just over 5000 conulariids from ten Ordovician formations in the Prague Basin (Czech Republic) exhibit invertebrate epibionts and/or attachment scars. The commonest epibionts are craniid brachiopods followed by bryozoans and edrioasteroids, which are invariably articulated. Less abundant are monoplacophorans, Sphenothallus sp., ?Lichenocrinus sp., and an indeterminate invertebrate. Epibionts occur on Anaconularia anomala, Archaeoconularia, Conulariella sp., and Pseudoconularia grandissima, though predominantly on A. anomala and Archaeoconularia from open shelf deposits in the Upper Ordovician Letná and Zahořany formations, in which conulariids are substantially more abundant than in other formations. Epibionts on a particular conulariid belong to a single species or up to three species and major taxa. Except for monoplacophorans, epibionts occur on the external surface of the conulariids, in some cases with brachiopods, bryozoans, or edrioasteroids present on all four faces. Brachiopods and edrioasteroids present on all four faces show little variation between the faces in their size range. Also, brachiopods show apparent random trending of the antero-posterior axis, while edrioasteroids on some specimens of A. anomala and Archaeoconularia are preferentially centered on or near the facial midline. On schott-bearing specimens of A. anomala exhibiting brachiopods and/or edrioasteroids, these and other epibionts are absent on the schott. Bryozoans on some A. anomala and Archaeoconularia cover portions of all four faces and corners, and on two specimens of A. anomala the schott, too, is encrusted. A similar case involving edrioasteroids on Archaeoconularia sp. from the Upper Ordovician Upper Tiouririne Formation of Morocco is documented.These results highlight the importance of Ordovician conulariids as biological substrates, especially in Perunica and South Polar Gondwana, and indicate that encrustation occurred both on live individuals and on dead ones. The corners and midlines influenced the settlement and subsequent growth of brachiopods and edrioasteroids, and conulariids bearing these epibionts were buried catastrophically.

A new craniid brachiopod genus from the terminal Ordovician Hirnantia fauna of Myanmar and South China

AbstractHirnantian costate craniides are rare in the world; many have only been defined using open taxonomic nomenclature and assigned to the genera Acanthocrania and Philhedra. New material from South China and Myanmar allows establishment of a new genus, Xenocrania, including its type species Palaeocyclus? haimei Reed from the Hirnantia fauna in northern Shan State, Myanmar. This genus is characterized by a unique ornamentation with a large degree of intraspecific variation in sympatric and allopatric populations. Three types of ornamentation (A, B and C) are recognized within the same population of this species, and even on the same individual. Based on this high degree of variation, we consider Xenocrania haimei and Acanthocrania yichangensis Zeng from the Hirnantia fauna of Yichang, western Hubei, South China to be conspecific. X. haimei was probably an opportunistic species, exhibiting considerable significant phenotypic pleiotropy (exemplified by a highly variable ornament) in response to severe ecological stress, particularly during the end Ordovician crisis, enabling the species to survive the extinction event. Geographically, Xenocrania gen. nov. occurs not only in the Hirnantia fauna of Myanmar (Sibumasu) and South China, but also in England (Avalonia), Poland (Baltica) and probably also Bohemia (Perunica). A further reassessment of many nominal or indeterminate taxa of Ordovician and Silurian craniides tentatively attributed to Philhedra, Acanthocrania and other related genera is needed.

Ordovician conulariids (Scyphozoa) from the Upper Tiouririne Formation (Katian), eastern Anti-Atlas Mountains, southern Morocco

Abstract Storm-dominated siliciclastic shelf deposits in the upper half of the Upper Tiouririne Formation (Upper Ordovician, upper Berounian– c. Katian 1–2) of southern Morocco contain large specimens of at least two species of Archaeoconularia ( A . aff. consobrina and A . cf. imperialis ). Pseudoconularia cf. grandissima occurs in basal beds of the formation, but is far less abundant than Archaeoconularia . The large size of the Archaeoconularia (>500 mm long in some cases) suggests gigantism induced by cold, nutrient-rich waters. Specimens preserving the apical end terminate in a schott, indicating that the conulariids were severed near the apex prior to final burial. Many of the Archaeoconularia occur in monospecific aggregations in which the component specimens exhibit preferential alignment, probably owing to entrainment and burial by storm currents or flows. Some Archaeoconularia are encrusted by edrioasteroids and/or craniid brachiopods, which in certain cases are so closely spaced as to interfere with growth. The edrioasteroids and brachiopods were probably epibionts attached to living, erect or semi-erect conulariids that were partially infaunal. More generally, Late Ordovician conulariid assemblages of South Polar Gondwana and adjacent terranes exhibit low generic diversity relative to those of low- to mid-latitude terranes (Baltica and Laurentia), and are dominated numerically by Archaeoconularia .

Sunken muscle scars in craniid brachiopods (Craniata); a long‐standing misconception

Since the early 19th century, depressions in, and holes piercing through, the lower (ventral) valves of craniid brachiopods have been described as ‘sunken muscle scars’. Examination of extant craniid material has shown that the characteristic surface texture of calcitic muscle scars, myotest, is not present in these so-called sunken muscle scars. Reconstruction of the musculature of a fossil specimen of Crania craniolaris with posteriorly directed, valve-piercing holes suggests that muscles could not have passed through these holes and been functional. It is proposed that recently discovered organic muscle attachment tissue that forms muscle attachment surfaces and organic rostella in some extant craniids was also present in fossil craniids and occupied so-called sunken muscles scars. Thus, in most cases, so-called sunken muscle scars are not muscle scars at all. New terminology is proposed for the organic muscle attachment tissues and so-called sunken muscle scars. The presence of calcitic and/or so-called sunken muscle scars introduces a significant level of morphological variation in some craniid genera and species. The taxonomy of craniid genera and species where the presence of so-called sunken muscle scars are part of the diagnosis or description should be reassessed.

Fossil craniid brachiopods (Craniata) of Australia and New Zealand

Three fossil craniid species from Australia are synonymised. Two species are transferred to two different genera, one to Danocrania and one to Novocrania; these species are described, figured and their geographic ranges illustrated. Five fossil craniid species from New Zealand, four of Novocrania and one of Valdiviathyris, are described, figured and their geographic ranges illustrated. The species described range in age from middle Paleocene to Recent. The paleoecology is summarised.

Middle Ordovician (Darriwilian) linguliform and craniiform brachiopods from the Precordillera (Cuyania Terrane) of west-central Argentina

AbstractMiddle Ordovician lingulacean, trematid, and craniid brachiopods are described and illustrated for the first time from the uppermost part of San Juan Formation limestones of the Precordillera Basin, west-central Argentina. Sampled beds fall within theAhtiella argentinabrachiopod Zone, which, according to associated conodonts, is of early-mid Darriwilian age. The fauna consists of the linguloideansGlossella cuyanican. sp. andLingulasma? sp., the discinoideanTrematissp., the siphonotretidChilcatreta tubulatan. gen. n. sp., and a conical shell that is referred provisionally to the order Craniida. The linguliforms from the Cuyania (Precordillera) terrane, although still poorly known, display close similarities to those inhabiting low-to-intermediate latitude palaeocontinents, particularly Laurentia and Baltica, in accordance with evidence from rhynchonelliform brachiopods.

Variations in the gut of craniid (inarticulated) brachiopods.

Specimens of six species (from two genera) of inarticulated craniid brachiopod were dissected and the gut examined and compared. The gut of the five Novocrania Lee & Brunton 2001 species were very similar, except for some variations in the configuration of the pylorus-intestine. The gut of Neoancistrocrania Laurin 1992 had two distinctly different features from Novocrania; the pharynx-esophagus-stomach forms a dorsally directed half loop and the pylorus-intestine is straight. Neoancistrocrania has four unique soft-tissue features and should remain a separate genus from Novocrania.

Craniid brachiopods: aspects of clade structure and distribution reflect continental drift (Brachiopoda: Craniiformea)

We present maximum likelihood and Bayesian inference relative time-tree analyses of aligned gene sequences from a worldwide collection of craniiform brachiopods belonging to two genera, Novocrania and Neoancistrocrania. Sequences were obtained from one mitochondrial and three nuclear-encoded ribosomal RNA genes from varying numbers of specimens. Data-exploration by network (splits) analyses indicates that each gene identifies the same divergent clades and (with one minor exception) the same inter-clade relationships. Neoancistrocrania specimens were found only in the Pacific Ocean, near Japan, on the Norfolk and Chesterfield Ridges, and near the Solomon Islands. The Novocrania clades, in approximate order of increasing distance from the root comprise 1. a ‘Northern’ clade of animals collected in the NE. Atlantic, W. Mediterranean and Adriatic; 2. a ‘Tethyan’ clade comprising animals from the E. Mediterranean, Cape Verde islands and the Caribbean (Belize and Jamaica); 3. a ‘NE. Pacific’ clade containing animals from Vancouver Island and from localities near Japan and south of Taiwan; 4. a ‘Southern’ clade that contains two widely separated subclades, one from New Zealand and the other with an extraordinarily wide distribution, ranging from near Japan in the north to the Chesterfield Ridge and Solomon Islands in the West, and in the East to the Galapagos Islands, the coast of South America (Chile) and Richardson seamount (off South Africa) in the South Atlantic. To the South, members of this clade were found in the Weddell, Scotia and Bellinghausen Antarctic Seas. The root of the extant craniid radiation was previously found (by relaxed-clock analysis) to lie on the branch connecting the two genera so that, in effect, the one clade of Neoancistrocrania serves to polarise evolutionary relationships within the several clades of Novocrania. As previously suggested, all results confirm that Neoancistrocrania is sister to the ‘Northern’ Novocrania clade, and this leads to a proposal that Neoancistrocrania represents one extreme of a wide range of variation in ancestral ventral valve mineralisation, speciation (∼90 Ma) resulting from competitive exclusion in rapidly-growing reef environments. To the extent possible, the identified molecular clades are correlated with named species of Novocrania. The reproductive and population biology of craniid brachiopods is not well known, but from available evidence they are considered to have low-dispersal potential and, except in enclosed localities such as cold-water fjords, to have small effective population sizes, features which are consistent with the observed divergent populations in well-separated localities. Exceptionally slow craniid molecular (rDNA) evolution is suggested by the short branch of Novocrania where it has been used as an outgroup for large-scale analyses of metazoans. Slow molecular evolution is also indicated by the existence of a distinct Tethyan clade, reflecting restricted dispersal at former times, and by the uniform, short, genetic distances and exceptionally wide geographical distribution of the Southern clade. Thus, the geographical distribution and phylogenetic divergence of craniid brachiopods is an example of phylotectonics, in which relationships revealed by phylogenetic analyses reflect opportunities for dispersal and settlement that were created by tectonic plate movements associated, in this case, with opening and closure of Tethys and the breakup of Gondwana. Molecular dating of craniid divergences and radiochemical dating of tectonic events thus illuminate one another. © 2014 The Linnean Society of London

The muscles, body wall and valve-opening mechanism of extant craniid (inarticulated) brachiopods

Specimens of six species of craniid brachiopod were dissected and the musculature, body wall and mantle were examined. New names are proposed for the “brachial protractor” and “brachial retractor” muscles. The “brachial elevator” muscles are part of the anterior adductor muscles, a small bundle of translucent quick-muscle partially enclosed by a larger, curving bundle of the dark-coloured slow-muscle. A new ring muscle is described. The lophophore arms are extended and retracted by the hydrostatic skeleton and brachial muscles respectively. The valves of Novocrania are probably opened by the creation of hydrostatic pressure, within a newly described coelomic chamber, by contraction of the oblique lateral muscles. Neoancistrocrania has an extra pair of dorsal mantle canals arising at the posterior and a dorsally directed pouch in the body wall.

Influence of atrypid morphological shape on Devonian episkeletobiont assemblages from the lower Genshaw formation of the Traverse Group of Michigan: A geometric morphometric approach

Atrypids examined from the lower Genshaw Formation of the Middle Devonian (early middle Givetian) Traverse Group include a large assemblage of Pseudoatrypa bearing a rich fauna of episkeletobionts. We identified two species of Pseudoatrypa – Pseudoatrypa lineata and Pseudoatrypa sp. A based on ornamentation and shell shape. Qualitative examination suggested that the former had fine-medium size ribbing, narrow hinge line, widened anterior, gentle to steep mid-anterior fold, a more domal shaped dorsal valve, and an inflated ventral valve in contrast to the coarse ribbing, widened hinge line, narrow anterior, gentle mid-anterior fold, arched shape dorsal valve, and flat ventral valve of the latter. Geometric morphometric analysis supported two statistically different shapes ( p < 0.01 ) for the two distinct species. This study further examined these atrypids to investigate the influence of morphology on episkeletobiont settlement on the two Pseudoatrypa species. Among the 343 atrypid hosts examined, nearly 50% were encrusted by episkeletobionts. Common encrusters included microconchids, bryozoan sheets, and hederellids. Less common encrusters included auloporid corals, cornulitids, tabulate corals, Ascodictyon, craniid brachiopods, and fenestrate bryozoans. Hederellids, auloporid corals, cornulitids, and tabulate corals encrusted a few living Pseudoatrypa hosts, but determination of pre- or post-mortem encrustation by the majority of episkeletobionts is equivocal. In a very few cases, episkeletobionts crossed the commissure indicating the death of the host. Some episkeletobionts, microconchids and the sheet bryozoans, were more common on Pseudoatrypa lineata, which exhibited more dorsal-ventral convexity than Pseudoatrypa sp. A. Perhaps, P. lineata may have provided a larger surface area for episkeletobiont settlement relative to Pseudoatrypa sp. A. In both the host species, encrustation was heaviest on the convex dorsal valve. This suggests that most of the encrustation occurred in a reclining, dorsal-valve-up life orientation of both species, in which the convex dorsal valve was exposed in the water column and the ventral valve remained in contact with the substrate. However, life orientations of these atrypid species could not be confidently predicted simply from the location preferences of episkeletobionts alone, as the life orientation of the host would also have been a hydrodynamically stable orientation of the articulated shell after death. Most episkeletobionts encrusted the posterior region of both dorsal and ventral valves of the two species, which suggests that the inflated areas of these valves, when exposed, favored the settlement of most episkeletobiont larvae.

Crystallography of the Calcitic Foliated-Like and Seminacre Microstructures of the Brachiopod Novocrania

Previous studies on the calcitic seminacre of the craniid brachiopod Novocrania have never fully resolved the crystallography of its constituent calcite crystals. With this aim, we studied the tablets forming the foliated-like and seminacre layers of this brachiopod by means of scanning electron microscopy coupled to electron backscatter diffraction. In both cases, tablets are monocrystalline and have a common crystallographic structure. Their c axes lie approximately parallel to the shell surface, and, for those tablets forming the internal shell ribs, they are also parallel to the rib elongation. There is no consistency in the orientation of the a axes in the different plates. Crystal competition processes appear to be responsible for this fiber texture. The tablets are bounded by planar rhombohedral faces. The main, innermost surface is not a crystal face but marks the boundary of the crystal with the mantle epithelium. Our data also show that, during spiral growth, the crystal axes of seminacre tablets remain stationary. Calcite twins occasionally develop in the species Novocrania anomala. The foliated-like and seminacre microstructures are crystallographically dissimilar to the foliated layer of molluscs but similar to the foliated layer of bryozoans. The relationship of brachiopod seminacre to the molluscan nacre is also discussed.

High resolution distribution of magnesium and strontium and the evaluation of Mg/Ca thermometry in Recent brachiopod shells

High resolution distribution of magnesium and strontium determined by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) are presented in this study for Recent brachiopod shells. The concentration of magnesium and strontium decreases in a similar fashion from the outer to inner regions of shells of rhynchonelliform species but remains unaltered in craniid brachiopods. In rhynchonelliform brachiopods with low-magnesium shells, there is a characteristic chemical profile with an abrupt decrease in magnesium concentration from the primary layer towards the secondary layer until it reaches a region in which the values are almost constant. In addition, there is a proportional relationship in magnesium concentration between primary and secondary layers. Both findings demonstrate the biological control in magnesium incorporation in rhynchonelliform brachiopods confirming previously reported findings. Calculated Mg/Ca ratios based on magnesium concentrations within the innermost region of the secondary layer show that rhynchonelliform brachiopods can record seawater temperature. This finding opens up the possibility of using Mg/Ca (palaeo) thermometry even within the context of biological control and the potential application of Mg/Ca ratios as a seawater temperature proxy in fossil brachiopods.

Crystallography of craniid brachiopods by electron backscatter diffraction (EBSD)

ABSTRACTElectron backscatter diffraction (EBSD) is used to determine the detailed crystallographic orientation of calcite crystals of craniid brachiopods in the context of shell ultrastructure. Sections of shells of two Recent species, Novocrania anomala and Novocrania huttoni, are analysed to provide 3D crystallographic patterns at high spatial resolution. The c-axis of semi-nacre calcite crystals is oriented parallel to the laminae that define the ultrastructure of the secondary layer. This orientation differs from that of rhynchonelliform calcitic brachiopods where the c-axis is perpendicular to the length of morphological fibres and to the shell exterior.

Comparison of the Crystallographic Structure of Semi Nacre and Nacre by Electron Backscatter Diffraction

Aragonite nacre is commonly found in the shells of molluscs, while semi nacre has been observed in the shells of organisms from two phyla: the Brachiopoda and the Bryozoa. Calcite semi nacre and aragonite nacre display similar morphologies with laminae composed of tablets that grow by screw dislocation. This study uses electron backscatter diffraction to compare the crystallography of calcite semi nacre from the shell of the Craniid brachiopod Novocrania huttoni with aragonite nacre from the shell of the bivalve mollusc Mytilus edulis. Semi nacre and nacre are similar in morphology but ultimately have different crystallography. In N. huttoni calcite semi nacre, the c-axis lies parallel to the laminae of the secondary layer of the shell. In comparison, the c-axis of aragonite nacre in M. edulis is orientated perpendicular to the laminae. The crystallography of calcite semi nacre in the secondary layer of N. huttoni is similar to the crystallography of skeletal ultrastructures produced by bryozoans, while it differs from the crystallography described in other brachiopod genera.

Hyperspectral cathodoluminescence imaging of modern and fossil carbonate shells

Optical cathodoluminescence (CL) is commonly used to identify diagenetically altered carbonate fossils, yet such an interpretation is problematic as present‐day carbonate shells may also luminesce. Hyperspectral CL imaging combines CL microscopy and CL spectroscopy to quantitatively analyze luminescence emission. Cold optical CL and hyperspectral CL imaging were carried out on four modern biominerals, a Rhynchonelliform brachiopod, a Craniid brachiopod, a bivalve, and the eggshell of the domestic fowl. A fossil Craniid brachiopod was analyzed to compare luminescence emission with that from the modern Craniid brachiopod. The beam conditions used for optical CL vary between studies, which hinders the direct comparison of CL analyses. This study assesses the effect of beam current and beam diameter on the intensity of luminescence emission. By characterizing the effect of beam conditions on different CaCO3 biominerals, comparisons can be made between CL studies. Hyperspectral CL imaging can be carried out in combination with WDS element analysis. By comparing hyperspectral CL images with element maps the causes of luminescence can to some extent be determined. The intensity of luminescence emitted from the modern biominerals differs under the same beam conditions. All four modern shells emit blue luminescence. In N. anomala, there is a correlation between Mn2+ concentration and luminescence intensity in the 620‐ to 630‐nm wavelength band, which is apparent in the inner region of the shell. The fossil Craniid also emits blue luminescence, and texture within the shell wall is apparent; however, the luminescence emission between 620 and 630 nm that is evident in N. anomala is absent.

Growth of protein–doped rhombohedra in the calcitic shell of craniid brachiopods

The secondary shell of the living inarticulated brachiopod Neocrania consists of calcitic laminae interleaved with organic sheets, predominantly a 44 kDa protein with high levels of aspartic acid–asparagine and glutamic acid–glutamine. Laminae consist of tabular (01.4) rhombohedra that are composed of spherular or rhombohedral granules, ca. 30 nm in size. Rhombohedra increase by planar or spiral growth as granular, monolayered plates that commonly act as foundations for multilayered tablets up to 300 nm or so high. Rough (0k.l) faces, kinked by cleavage, usually develop at either end of the long diagonals of rhombohedra, the edges of which may support ramparts that can accrete centripetally to enclose any organic material situated at tablet centres. Induced degradation by proteinase K shows that sectors subtended by (0k.l) steps are doped by a fibrous polymer, identified as an exclusively intralaminar glycosylated 60 kDa protein. A 44 kDa protein has also been extracted from laminae and is presumably incorporated into tablets by centripetally growing ramparts.

Crinoids, hardgrounds, and community succession: The Silurian Laurel—Waldron contact in southern Indiana

Halleck, Margaret S.: Crinoids, hardgrounds, and community succession: The Silurian Laurel-Waldron contact in southern Indiana. The uppermost surface of the Silurian Laurel Limestone at its contact with the Waldron Shale in southeastern Indiana was a hardground lithified prior to the deposition of the Waldron. Evidence for this conclusion is the presence of attached palmate crinoid roots, auloporid corals, and craniid brachiopods on the Laurel surface; the irregularity of the contact with the Waldron; and a pyritic veneer at this contact. The hardground apparently had a submarine origin. In addition to the attached epifauna mentioned above, algal-sediment ‘clods’ formed on this surface. Some of these accumulated around the crinoid stems, causing them to produce cirral extensions. The resulting community was a crinoid ‘meadow’ with algal growths forming sediment traps around and between the crinoids. Later stages of Waldron Shale deposition led to the development of a soft-bottom community.