Gordon B. Curry

Biology of Living Brachiopods

Publisher Summary This chapter describes the biology of living brachiopods. The Brachiopoda are significant components of the early Cambrian marine Faunas and are therefore one of the few phyla to be represented of the Phanerozoic era, which extends from the first widespread appearance of organisms with mineralized skeletons until modern times. The objective of chapter review is to chronicle some of the important biological work conducted over the past 25 years and to present an overview of current trends in brachiopod biology. Moreover, many of the recent studies of living brachiopods owe their motivation to a desire to improve palaeontological interpretation of the group. The scaling patterns of brachiopod tissue and other components in relation to total size and their morphological architecture show significant differences from the bivalves and may impose important constraints. Moreover, a general impression of many living articulate brachiopods is of a relatively small organism, in terms of organic tissues, inhabiting a relatively large space, defined by the shell. Brachiopods approximate spherical shapes, as much as their growth patterns and articulation systems allow. This chapter concludes that the brachiopod biomineralization system is ideally suited for the investigation of the interaction between the organic and the inorganic phases during shell growth.

Age, evolution and tectonic history of the Highland Border Complex, Scotland

I. ABSTRACT: Research interest in the Highland Border Complex has been pursued sporadically during the past 150 years. The results and conclusions have emphasised the problems of dealing with a lithologically disparate association which crops out in isolated, fault-bounded slivers along the line of the Highland Boundary fault. For much of the present century, the debate has centred on whether the rocks of the complex have affinities with the Dalradian Supergroup to the N, or are a discrete group. Recent fossil discoveries in a wide variety of Highland Border rocks have confirmed that many are of Ordovician age, and hence cannot have been involved in at least the early Grampian deformational events (now accurately dated as pre-Ordovician) which affect the Dalradian Supergroup. Such palaeontological discoveries form the basis for a viable biostratigraphical synthesis. On a regional scale, it is apparent that the geological history of the Highland Border rocks must be viewed in the context of plate boundary tectonism along the entire northwestern margin of Iapetus during Palaeozoic times.II. ABSTRACT: Silicified articulate brachiopods from the Lower Ordovician (Arenig) Dounans Limestone are extremely rare but the stratigraphically diagnostic genera Archaeorthis Schuchert and Cooper, and Orthidium Hall and Clarke, have been identified. In addition, three specimens with characteristic syntrophiid morphology have been recovered. Inarticulate brachiopods are known from Stonehaven and Bofrishlie Burn near Aberfoyle, and have also been previously recorded from Arran.III. ABSTRACT: Micropalaeontological investigation of the Highland Border Complex has produced a range of microfossils including chitinozoans, coleolids, calcispheres and other more enigmatic objects. The stratigraphical ranges of the species lie almost entirely within the Ordovician and reveal a scatter of ages for different lithologies from the Arenig through to the Caradoc or Ashgill, with a pronounced erosional break between the Llandeilo and the Caradoc.IV. ABSTRACT: A Lower Ordovician (Arenig Series) silicified ostracode fauna from the Highland Border Dounans Limestone at Lime Craig Quarry, Aberfoyle, Central Scotland, represents the earliest record of this group of Crustacea from the British part of the early Palaeozoic ‘North American’ plate.V. ABSTRACT: Palaeontological age determinations for a variety of Highland Border rocks are presented. The data are based on the results of recent prospecting which has demonstrated that macro- and microfossils are present in a much greater range of Highland Border lithologies than previously realised. Data from other studies are also incorporated, as are modern taxonomie re-assessments of older palaeontological discoveries, in a comprehensive survey of Highland Border biostratigraphy. These accumulated data demonstrate that all fossiliferous Highland Border rocks so far discovered are of Ordovician age, with the exception of the Lower Cambrian Leny Limestone.VI. ABSTRACT: The Highland Border Complex consists of at least four rock assemblages: a serpentinite and possibly other ophiolitic rocks of Early or pre-Arenig age; a sequence of limestones and conglomerates of Early Arenig age; a succession of dark shales, cherts, quartz wackes, basic lavas and associated volcanogenic sediments of Llanvirn and ? earlier age; and an assemblage of limestones, breccias, conglomerates and arenites with subordinate shales of Caradoc or Ashgill age. At least three assemblages are divided by unconformities and in theirmost general aspect have similarities with coeval rocks in western Ireland.The Highland Border Complex probably formed N of the Midland Valley arc massif in a marginal sea comparable with the Sunda shelf adjacent to Sumatra–Java. Strike-slip and thrust emplacement of the whole Complex in at least four episodes followed the probable generation of all or part of its rocks by pull-apart mechanisms.

The significance of a reliable Ordovician age for some Highland Border rocks in Central Scotland

A Lower Arenig fauna with North American affinities has been rediscovered at Dounans, Aberfoyle, Central Scotland. This discovery makes part of the Highland Border Complex younger than the adjacent Dalradian rocks, and suggests a provenance from the S.

Use of stable oxygen isotope determinations from brachiopod shells in palaeoenvironmental reconstruction

Abstract Stable oxygen isotope analyses were obtained from fossil brachiopod shells from a shallow marine deposit of Upper Pleistocene age (approximately 80 ka) in New Zealand as part of a palaeoenvironmental investigation. Bulk analyses of entire shells of Calloria inconspicua yielded highly variable results (a range of 2.30‰), rendering these data of limited use as palaeoenvironmental proxies. Attempts to obtain consistent oxygen isotope values by removing areas of the brachiopod shell thought to be prone to oxygen isotope disequilibrium effects (‘vital effects’) revealed that the matching anterior portions of ventral and dorsal valves from the same individual (which were secreted at the same time) also yielded different oxygen isotope ratios. The dorsal valve δ18O values were higher and less variable than those obtained from the ventral valve of the same individual. The investigation was then extended to living representatives of the same species from a similar shallow water habitat from the South Island of New Zealand. The pattern of dorsal valves yielding higher and less variable oxygen isotope values than matching areas of the ventral valves was repeated in seven out of eight individuals investigated, although there was considerable variation in the absolute values from specimen to specimen. Contrary to common practice therefore, it seems that in this species it is the much thinner and lighter dorsal valve that provides a more consistent isotopic measurement. If converted into absolute temperature estimates, the dorsal valve measurements correspond to a temperature midway between the mean and maximum annual temperature experienced by this species in its present-day habitat, which may make it acceptable as a palaeoenvironmental indicator. The high level of variation between individuals (including an inferred temperature from one ventral valve above the mean maximum temperature experienced) indicates that a range of individuals needs to be investigated in any palaeoenvironmental investigation to avoid misleading interpretations. However, intra- and inter-specimen variation in isotopic composition may provide valuable palaeobiological information on growth rates, metabolism and possibly also pathological conditions in the past.

Preservation of fossil biopolymeric structures: Conclusive immunological evidence

Abstract Immunological assays are highly favoured for their ability to readily discriminate subtle structural differences in complex biopolymers, such as proteins and polysaccharides. Immunological reactions previously reported with extracts from biominerals at least 70 Myr old have fuelled hopes that such biopolymeric structures can survive the process of fossilization. We have raised antibodies against biopolymers from a range of Recent brachiopod shells to reconstruct a fine-grained pattern of phylogenetic relationships. Using the same antibodies, the phylogenetic affinities of fossil relatives were tested. Immunological reaction patterns for Plio-Pleistocene shells were essentially identical to the patterns of modern shells (although the breadth of reactivity was narrowed) and entirely consistent with current systematic interpretations. Older samples (>4–21 Myr) were immunologically reactive, but failed to satisfy the criterion of systematic specificity. Our results provide an unequivocal demonstration that original macromolecular structures capable of yielding systematic information are preserved and accessible for immunological analysis for at least two million years. Non-specific reactions observed with the older material may relate in part to formation of mineral-induced diagenetic determinants (MIDDs).

Stable carbon and oxygen isotope compositions of mollusc shells from Britain and New Zealand

Abstract Stable carbon and oxygen isotope analysis of the carbonate shells of two fossil mollusc species from the Plio-Pleistocene of New Zealand and two Recent species from the west coast of Scotland has revealed an unexpectedly high degree of variability for each species and a positive correlation between δ 13 C and δ 18 O in each case. This phenomenon may be due to kinetic isotope effects which are inherent in fastgrowing shells or areas of shell. If this is the case then equilibrium isotope partitioning may not have had time to occur before the completion of calcite precipitation. Kinetic effects would tend to favour the lighter isotopes of both carbon and oxygen; it is therefore the highest δ 13 C and δ 18 O values that are most likely to reflect equilibrium with the environment. Very small carbonate particles often give particularly low δ 13 C and δ 18 O values. These results have implications for the use of isotopic data in environmental reconstruction based on fast growing shells and may also be applicable to other carbonate precipitating organisms.

An intracrystalline chromoprotein from red brachiopod shells: Implications for the process of biomineralization

1. The red colour of some terebratulid brachiopod shells is caused by a small chromoprotein that occurs within the calcium carbonate matrix of the shell. 2. This carotenoid-protein complex was isolated from within the calcite shell of three different brachiopod genera and may therefore be involved in the process of biomineralization. 3. The apparent molecular weight of this protein, as judged by SDS-PAGE, is 6.5 kDa. 4. The partial N-terminal amino acid sequence of the protein is virtually identical in three different brachiopod genera, indicating homology. 5. Two carotenoids are present in Terebratella sanguinea: canthaxanthin and the tentatively identified monoacetylinic analogue of astaxanthin.

Oxygen isotope composition in Modiolus modiolus aragonite in the context of biological and crystallographic control

Abstract Living systems exert exquisite control on all aspects of biomineral production and organic components, including proteins, are essential to this biological control. The protein-rich extrapallial (EP) fluid of bivalve molluscs is a strong candidate for the source of such proteins. Differences in calcium carbonate polymorphs between Modiolus modiolus and Mytilus edulis are concurrent with differences in EP fluid protein profiles. In conjunction with this biological control is the environmental influence which is interpreted using proxies such as δ18O to determine the history of ambient seawater temperature. In the horse mussel, Modiolus modiolus, the difference in oxygen isotope fractionation in the nacreous aragonite and the prismatic aragonite layer results in respective δ18O values of 2.1±0.2% and 2.5±0.2‰. These δ18O values result in estimates of ambient seawater of 12.1±0.6°C and 10.2±0.6°C for nacreous and prismatic aragonite, respectively. Electron backscatter diffraction is used here to determine the crystallographic orientation at high spatial resolution, allowing the measurements of stable isotopes to be accurately mapped in terms of shell architecture. These preliminary data suggest that it is essential to account for both polymorph and crystal habit when deciphering ambient seawater temperature using δ18O as a proxy.

Oogenesis in the articulate brachiopodTerebratulina retusa

A detailed ultrastructural description of oogenesis is presented for the articulate brachiopodTerebratulina retusa (Linnaeus), based on collections made between October 1985 and October 1986 from the Firth of Lorn, west coast of Scotland. Oogenesis has been divided into six stages, defined according to ultrastructural changes, which are thought to be important steps in the process of vitellogenesis. Special attention has been given to the possible mechanisms involved in the acquisition and assimilation of nutrients within the differentiating oocyte. Each vitellogenic oocyte is contained within a follicular envelope which is attached to a genital lamella. As maturation proceeds, accessory cells proliferate within the follicular envelope. A variety of intra-accessory cell and oocyte/accessory cell communications were identified. The process of elaboration of the oolemma is reported in detail. Lipid was identified as the major nutrient reserve of the oocyte. Late mature oocytes measure ~130 µm in diameter when spawned. The process of oosorption is also documented.

Functional morphology of the gonads of the articulate brachiopodTerebratulina retusa

The reproductive anatomy, and ultrastructural features of the gonads of the articulate brachiopodTerebratulina retusa (Linnaeus), are documented based on collections made between October 1985 and October 1986 from the Firth of Lorn, west coast of Scotland. This species is dioecious, and maturity is achieved in both sexes at shell lengths greater than ~5.5 mm. There is no obvious external sexual dimorphism except for slight differences in the coloration of the gonads; testes are white/cream, ovaries are yellow/orange. The gonads occur as four palmate lobes, a pair in each valve. Gonads are formed within a mantle sinus (vascula genitalia), which is an anterior extension of the coelom, that opens posteriorly into the visceral cavity and to the exterior via a pair of metanephridia. The latter serve as gonoducts during spawning. Gametes are borne on genital lamellae formed from a reticulate lattice of connective tissue. The lamellae are an extension of the ileoparietal band and are fused along one margin to the inner mantle membrane. Developing oocytes are closely affixed to the genital lamellae and originate from a pool of proliferating germ cells at its base. Vitellogenic oocytes that are at an advanced stage are released from the genital lamellae, but are retained within thevascula genitalia. Liberated oocytes continue to accumulate yolk and eventually occlude thevascula genitalia, before being spawned. Coelomocytes were identified within the gonads. In spent females these cells appear to be phagocytic and involved in the resorption of necrotic material, while in the male they may serve as nutritive cells.