Segmental growth in planulate ammonites: inferences on costal function

Checa, Antonio & Westermann, Gerd E. G. 1989 01 15: Segmental growth in planulate ammonites: inferences on costal function. Lethaia , Vol. 22, pp. 95–100. Oslo. ISSN 0024–1164.
In planulate Ammonitina, the directions of costae and their parts coincide with the growth lines, both being accreted in parallel and subtriangular increments, i.e. segments. This implies that the growing margin was consistently corrugated (plicated) parallel to the edge of the peristome. The adventral separation of the ribs caused by the coiling increased with whorl involution and was compensated for by costal division into primaries and secondaries. We propose that costation of the shallow-water, nekto-benthic plandates reduced the stiffness and increased effective thickness of their growing peristome. Ribs functioned (primarily or secondarily) as a protection for the immature, fragile aperture against predators and impacts.□ Ammonite shell, Jurassic, morphology, growth lines, ornamentation, costae .     

Characteristics of shell microstructure and growth analysis of the Antarctic bivalve <Emphasis Type="Italic">Laternula elliptica</Emphasis> from Lützow-Holm Bay,Antarctica

Growth performance of the Antarctic bivalve Laternula elliptica was examined both by shell microstructural observation and by applying a fluorescent substance, tetracycline, as a shell growth marker. The shell was composed of two calcareous layers: the thick outer layer was homogeneous or granular in structure and the thin inner layer was nacreous. The architecture of Antarctic L. elliptica was different from that of temperate L. marilina, and the ratio of thickness between the outer and inner layers appeared to be different. The growth rate of the nacreous layer was analyzed to be very low. High correlations were found between the major axis of chondrophore and both shell length and shell dry weight, respectively. It is suggested that the chondrophore is an appropriate growth indicator, and combining the information of growth increments with the fluorescent method may be useful in estimating the bivalve growth performance in the Antarctic sea.     

Rib fabrication in Ostreoidea and Plicatuloidea (Bivalvia,Pteriomorphia) and its evolutionary significance

Ribs of Ostreoidea and Plicatuloidea are defined as antimarginal, that is, perpendicular to the margin throughout growth. Morphogenetically, these ribs are unique, since, unlike radial ribs, they are secreted by a homogeneous mantle margin. Based also on the reconstructed shell secretion cycle in Bivalvia, we propose that ribs of Ostreoidea and Plicatuloidea are formed by a mantle margin which, upon extension from the shell margin, stretches and folds by taking the preformed ribs as templates. In extending perpendicular to the margin (as in all Bivalvia growing isometrically), such a mantle extends the rib pattern antimarginally. Ribs of this kind are purely mechanical structures, as their arrangement depends on the mechanical properties of the mantle and on the environmental conditions. This explains the high irregularity of such ribbing patterns. The presence of antimarginal ribs in both the Ostreoidea and Plicatuloidea sheds light on their origin. The first known oyster, Actinostreon cristadifformis, probably derived from an antimarginally ribbed Prospondylidae gen. indet. in the Late Permian or Early Triassic. Antimarginally ribbed Triassic species formerly included in Placunopsis originated both the Dimyidae Atreta in the Late Triassic and Enantiostreon in the Mid Triassic, which was transitional to Plicatulidae. Therefore, Dimyidae and Plicatulidae are closely connected and grouped under Plicatuloidea, to which Ostreoidea is phylogenetically unrelated.     

A metabolic model for the determination of shell composition in the bivalve mollusc, Mytilus edulis

Rosenberg. G. D. & Hughes, W. W. 1991 01 15: A metabolic model for the determination of shell composition in the bivalve mollusc, Mytilus edulis. Lethaia, Vol. 24. pp. 83–96. Oslo. ISSN 0024–1164. This research describes compositional variations within the shell of the extant mussel Mytilur edulis and proposes that they are produced by metabolic gradients within the shell-secreting mantle. Because we have previously proposed that the same metabolic gradients are responsible for variations in shell form (curvature), we establish here a model for molluscan shell growth integrating. for the first time. shell form and composition with mantle metabolism. The electron microprobe was used to measure the distribution of Mg. S, and Ca in the outer calcitic shell layer of sectioned. polished, and either A1- or C-coated shell. Mg/Ca and S/Ca ratios in the outer shell are respectively 1.25 and 1.40 times higher along slow-growing, commissure-umbo axes of high shell curvature and high metabolic activity than along rapidly growing axes of low curvature and low metabolic activity. The ratios within the inner surface of the calcitic shell layer decline most rapidly along commissure-umbo axes where mantle metabolic activity also declines rapidly. We reject the null hypothesis, generally at high levels of significance (1-tests. F-tests. regression analyses, and discriminant analysis. with p 4 0.01) that there is no difference in either Mg or S concentration in sections of the calcitic shell layer that differ in shell curvature and mantle metabolic activity. We conclude that calcium (mineral)-rich portions of shells are energctically less costly to produce than matrix or minor element-rich portions. in agreement with the proposal that natural selection favors mineral-rich shells because they are more efficient to produce than matrix-rich shells. Among-specimen differences are also highly significant (mixed model ANOVA). This confirms our assertion that paleontologists need to describe variations in skeletal composition among populations and throughout ontogeny as systematically as classical taxonomists describe morphology. if ever the environmental and the genetic influences on skeletal composition are to be distinguished. Bivalves. biomineralization, shell composition. magnesium, sulfur, calcium, metabolism, growth. Mytillus edulis     

Growth line deposition and variability in growth of two circumpolar bivalves (Serripes groenlandicus, and Clinocardium ciliatum)

Growth patterns of two common circumpolar bivalves, the Greenland cockle (Serripes groenlandicus), and the hairy cockle (Clinocardium ciliatum) have been used in previous studies to reconstruct environmental conditions in the arctic. To date, there has been no direct determination that growth lines in either species are deposited periodically, and there has been no examination of factors affecting growth. We placed calcein-marked individuals of both species on oceanographic moorings in two fjords (Rijpfjord and Kongsfjord) in the Svalbard archipelago for one and two (Kongsfjord only) years. Growth patterns were compared with concurrent in situ temperature and fluorescence data in order to assess environmental controls on growth. Dark growth lines are evident on the outer shell surface and internally in shell cross section in both S. groenlandicus and C. ciliatum, and both species deposited only one line per year, unequivocally confirming that internal lines are deposited annually. Growth line deposition in both species began in late summer to early fall, before the seasonal decline in temperature. There was no difference in growth of S. groenlandicus between the two fjords despite differences in water temperature (3°C), fluorescence (nearly threefold) and the onset and duration of the winter season. C. ciliatum, however, grew approximately 2.8 times faster in the warmer, more food-rich Kongsfjord than in Rijpfjord. Subannual lines were counted in two individuals of each species from each fjord, but deposition of these lines was not clearly related to number of growing days estimated by temperature and fluorescence.     

Eggshell structure, mode of development and growth rate in birds

The shell of an egg contributes to successful embryogenesis in many ways, such as through protection, respiration and water exchange. The shell is also the major source of calcium for the development of high-calcium consuming organs, e.g. the skeleton, muscles and brain. Some studies show, moreover, that growth rate may play a fundamental role in the pattern of skeletal development in birds: the faster the growth the less ossified the skeleton is at hatching. We predicted, therefore, that slow (precocial) and fast (altricial) growing bird species should lay eggs encased in shells with different structures adapted to support different rates of calcium removal by developing embryos. We tested this prediction by comparing the fine structure of the inner eggshell surface (mammillary layer) from 36 bird species belonging to 18 orders ranging from Struthioniformes to Passeriformes. Using scanning electron microscopy, we compared the mammillary layer of both non-incubated eggs and eggs at the time of hatching, i.e., before and after embryonic development and the accompanying calcium removal. The results were consistent with the prediction, i.e., the number of mammillary tips per unit of surface area was associated with mode of development and growth rate. The number was higher, and calcium removal was also more extensive, in shells from precocial bird species than in shells from altricial bird species.     

Structure of shells from eggs of kinosternid turtles

Shells from eggs of five species of kinosternid turtle (Sternotherus minor, Kinosternon flavescens, K. baurii, K. Hirtipes, and K. alamosae) were examined with light and scanning electron microscopy. Except for possible differences among species in thickness of eggshells, structure of shells from all eggs was similiar. In general, kinosternid turtles lay eggs having a rigid calcareous layer composed of calcium carbonate in the form of aragonite. The calcareous layer is organized into individual shell units with needlelike crystallites radiating from a common center. Most of the thickness of the eggshell is attributable to the calcareous layer, with the fibrous shell membrane comprising only a small fraction of shell thickness. Pores are found in the calcareous layer, but they are not numereous. The outer surface of the eggshells is sculptured and may have a thick, organic layer in places. The outer surface of the shell membrane of decalcified eggshells is studded with spherical cores which presumably nucleate growth of shell units during shell formation. The shell membrane detaches from eggs incubated to hatching, carrying with it remnants of the calcareous layer. Such changes in shell structure presumably reflect withdrawal of calcium from the eggshell by developing embryos.     

Biogenic and taphonomic processes affecting the development of shell assemblages: an actuopaleontological case study from mussel banks on North Sea tidal flats

Summary From spring 1997 to winter 2000, the composition and structure of epibenthic bivalve clusters and patches on a backbarrier tidal flat of the East Frisian Wadden Sea were continoously analyzed. The studied bivalve aggregates developed from intense and approximately simultaneous spatfalls of Mytilus edulis and Cerastoderma edule in 1996, after a severe winter (1995/96) with 64 days of driftice coverage. Spatfall occurred on a bare sandy tidal flat, whereas adjacent shell layers situated at the southern margin of the spatfall site were not colonized. Usually, such shell layers are the most common secondary hard substrates in the backbarrier area favorable for initial settlement of Mytilus larvae. The shell layers predominantly originate from erosion of former Mya arenaria and C. edule populations. So far, the studied bivalve aggregates are composed of approximately equal proportions of living specimens of both species, M. edulis and C. edule. The incorporated cockles were prevented from burrowing into the rediment by the coherent byssal mesh. In contrast to the results of previous studies, the great bulk of epibenthic living C. edule did survive for several years within the clusters. Therefore, the common terms ‘Mytilus banks’, ‘Mytilus patches’ or ‘Mytilus clumps’ may be too general and may erroneously imply a dominance of (or mono-specific composition by) M. edulis. In the fossil record, i.e. in diagenetically consolidated shell layers, the enforced epibenthic life-mode of C. edule and the remarkable species composition as well as the temporal development of the aggregates would not be recognizable.     

The development of growth lines on articulate brachiopods

Three types of growth lines are recognised on articulate brachiopod shells: (1) very fine diurnal growth lines formed by calcite increments at the shell margin, (2) seasonal growth lines, formed by inward reflection (doubling back) of the mantle edge, seen as concentric steps on the shell surface and marked by re-orientation of growth vectors evidenced by secondary shell fibres, (3) disturbance lines, formed by abrupt regression of the mantle edge, also seen as concentric steps on the shell surface, but indicated by a dislocation in the shell fabric. Lamellose and spinose ornaments of the sort seen in Tegulorhynchia are essentially genetically controlled. Periodic outgrowths from the outer mantle lobe secrete frills of primary shell that project from the shell surface and form short hollow spines where they cross the radial ornament. In longitudinal section spine formation is seen to involve gradual increase in the rate of secretion of primary shell followed by retraction, and often collapse, of the mantle outgrowth, accompanied by regression. Reflection of the mantle edge usually follows spine formation.     

Lobe formation and division in the foliose lichen <Emphasis Type="Italic">xanthoparmelia conspersa</Emphasis>

New lobe development and lobe division was studied in the foliose lichen Xanthoparmelia conspersa (Ehrh. ex. Ach.) Hale. In thalli with either the centre or margin removed, the inside edge of the perimeter, the outer edge of the reproductive centre, and fragments derived from the thallus perimeter all regenerated growing points (‘lobe primordia’) within a year. Thalli possessing isidia had the greatest ability to regenerate growing points. In reproductive thalli, there was a positive correlation between the density of new growing points and thallus size. When fragments were cut from the perimeters of mature X. conspersa thalli and glued to pieces of slate, the ratio of growing points to mature lobes increased over 54 months. Lobes within a thallus exhibited different degrees of bifurcation. In some bifurcating lobes, the point of origin of the bifurcation advanced at the same rate as the lobe tips over 4 months but in most lobes, the bifurcation point either advanced less rapidly than the lobe tips or retreated from its original location. Removing adjacent lobes had no significant effect on the radial growth of a lobe over 4 months or on the location of the bifurcation point but it increased the number of growing points. These results suggest that for X. conspersa: 1) all portions of of thalli can regenerate growing points, 2) few growing points actually develop into mature lobes, 3) individual lobes within a thallus grow and divide differently, and 4) adjacent lobes inhibit the development of growing points on their neighbours.     

Bivalves with 'concrete overcoats': Granicorium and Samarangia

Two veneroidean bivalves Granicorium indutum from Australia and Samarangia quadrangularis from the tropical Indo-Pacific region, cement a thick, hard layer of sand over most of their shells. In Granicorium this layer forms low commarginal ribs while in Samarangia it forms more prominent radial features. Sand grains are cemented to the shell and to each other with growths of a crystalline aragonitic cement similar in morphology to inorganic marine cements. Both species secrete mucus layers at the growing shell margin which initially hold the sediment grains together and form a substrate for the nucleation and growth of calcium carbonate crystals. The ribs of Samarangia are formed by the accretion of successive sheets of spherulitic growths. In G. indutum , the middle and outermost of two inner mantle folds are large, glandular and capable of considerable extension beyond the shell margin. Mucus secreted by the folds contains abundant bacteria and small calcium carbonate crystals. It is proposed that initial nucleation of the calcium carbonate cement takes place within this biofilm possibly mediated by the bacteria. The function of the sand layers is unknown but predation resistance and protection of the shells from endobionts are the most likely possibilities.     

The Micro/Nanostructure Characteristics and the Mechanical Properties of Hemifusus tuba Conch Shell

<正> The mollusk shell mobilizes calcium from environment for skeletal mineralization.This occurs through synthesizing solidsin solution in the presence of organic molecules of specific interior regions of the conch shell.The ultrastructure and microhardnessof the Hemifusus tuba conch shell living in the Huang/Bo sea area are investigated in the paper.It is shown that thecomposition and microstructure of the mollusk shell vary in different positions.The prodissoconch shell consists only of aragonitewith the crossed-lamellar microstructure.While the spiral shell and the body shell of the Hemifusus tuba conch shell arecomposed of one calcite layer and several aragonite layers.The calcite layer consists of cylindrical grains,but the aragonitelayers are crossed-lamellar ultrastructure at three size scales.The minimum structure size (the third-order lamella) is at about20 nm - 80 nm.The margin of shell aperture is only composed of calcite with cylindrical grains.This natural optimization of theshell microstructure is intimately due to the growth of the Organic matrix.At different positions the microhardness of molluscshell is different due to different crystal structures and crystal arrangements.The growth process of shells allows a constantrenewal of the material,thus enabling their functional adaptation to external environments.     

Does Soil Organic Layer Thickness Affect Climate–Growth Relationships in the Black Spruce Boreal Ecosystem?

The observed long-term decrease in the regional fire activity of Eastern Canada results in excessive accumulation of organic layer on the forest floor of coniferous forests, which may affect climate–growth relationships in canopy trees. To test this hypothesis, we related tree-ring chronologies of black spruce (Picea mariana (Mill.) B.S.P.) to soil organic layer (SOL) depth at the stand scale in the lowland forests of Quebec’s Clay Belt. Late-winter and early-spring temperatures and temperature at the end of the previous year’s growing season were the major monthly level environmental controls of spruce growth. The effect of SOL on climate–growth relationships was moderate and reversed the association between tree growth and summer aridity from a negative to a positive relationship: trees growing on thin organic layers were thus negatively affected by drought, whereas it was the opposite for sites with deep (>20–30 cm) organic layers. This indicates the development of wetter conditions on sites with thicker SOL. Deep SOL were also associated with an increased frequency of negative growth anomalies (pointer years) in tree-ring chronologies. Our results emphasize the presence of nonlinear growth responses to SOL accumulation, suggesting 20–30 cm as a provisional threshold with respect to the effects of SOL on the climate–growth relationship. Given the current climatic conditions characterized by generally low-fire activity and a trend toward accumulation of SOL, the importance of SOL effects in the black spruce ecosystem is expected to increase in the future.     

Identification of ecophenotypic trends within three European freshwater mussel species (Bivalvia: Unionoida) using traditional and modern morphometric techniques

Most species of freshwater mussels (Unionoida) show a wide variability in shell form and size but an understanding of which factors determine unionoid morphology is poor. We identified ecophenotypic trends in shell and internal characters within three unionoid species from two habitat types (marinas and river) of the River Thames, UK, using traditional and modern morphometric techniques. In marinas, all species grew to larger maximum sizes than in the river, which might be a result of higher temperatures and phytoplankton densities in marinas. Unio pictorum in marinas was more elongated than in the river and Fourier shape analysis revealed a trend from dorsally arched river specimens to straight dorsal and pointed posterior margins in marina individuals. The degree of shell elongation and shape of dorso‐posterior margin were not associated with sediment composition, but were associated with the different hydrological characters of the two habitat types. Relative shell width was a poor indicator of collection site and influenced by allometric growth. Unlike U. pictorum, a difference in shell elongation of marina and river mussels could not be detected in Unio tumidus and Anodonta anatina. However, all three species showed the same trends regarding the shape of the dorso‐posterior shell margin. This shell character may thus have broad ecological significance and could have considerable utility to palaeontologists, taxonomists, and conservation biologists. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 814–825.     

Shell growth, reproduction and mortality of Ovula ovum in southern Kyushu, Japan

Seasonal shell growth, reproduction and mortality of the eggcowry Ovula ovum were studied from May 2004 to October 2006in southern Kyushu, Japan, an area at the northern margin ofits geographic distribution. Rapid shell growth was observedduring the period of warmer ocean temperature (May–October).Average shell growth rate of small cowries was 2.84 mm/week.Reproductive activities were observed during most of the yearexcept during the coldest period (March–April). Egg cowriesreach maturity at approximately 7 cm in shell length, and at1 year of age. Average shell length of brooding females andcopulating pairs (female and male) were 8.14 ± 0.40,8.17 ± 0.49 and 8.08 ± 0.43 cm (mean ±SE), respectively. High mortality rates (average 67.5%) wereobserved from December to May. The maximum numbers of emptyshells in the field (April 2005, May 2006) were seen duringthe period of the lowest ocean temperatures (March 24, 2005;March 7, 2006). This suggests that ocean temperature may bean important factor for egg cowry populations at the northernmargins of their geographical distribution, and that O. ovummay increase fitness with rapid shell growth and early age ofmaturation. (Received 11 January 2008; accepted 22 August 2008)     

Age,growth, and population structure of the smooth clam <Emphasis Type="Italic">Callista chione</Emphasis> in the eastern Adriatic Sea

The age, growth, and population structure of the smooth clam Callista chione were determined from samples collected by hydraulic dredge and SCUBA at four locations in the eastern Adriatic during 2007 and 2008. The age of 436 clam shells was determined from internal growth lines present in shell sections, and the timing of growth line formation was ascertained from monthly collections of clams to occur between August and September when sea water temperatures were maximal. In addition, age of 30 older individuals was verified with acetate peels of polished and etched shell sections. Differences were apparent in the age structure and growth rates of clams collected from the four locations studied. Von Bertalanffy growth (VBG) curves obtained for clams from these locations were L _t  = 72.4 (1−e^{−0.25(t − 2.68)}) (Rab Island), L _t  = 74.5 (1−e^{−0.15(t + 0.57)}) (Pag Bay), L _t  = 79.3 (1−e^{−0.34(t − 0.97)}) (Cetina estuary), and L _t  = 82.5 (1−e^{−0.11(t + 2.88)}) (Kaštela Bay). The age of the clams ranged between 3 and 44 years; median clam ages were similar at three of the four locations (14, 12, and 12 years, respectively), but was significantly lower in the Cetina estuary (4 years). The VBG growth constants recorded from clams were within the range of values obtained for this species by previous authors. The observed local differences in population structure indicate different levels of exploitation and illustrate the need to establish long-term strategies for a sustainable exploitation of smooth clams in the Croatian Adriatic.     

Shell microstructure and mineralogy of the Littorinidae: ecological and evolutionary significance

An examination of the shell microstructure and mineralogy of species from 30 of the 32 genera and subgenera of the gastropod family Littorinidae shows that most species have a shell consisting of layers of aragonitic crossed-lamellar structure, with minor variations in some taxa. However, Pellilitorina, Risellopsis and most species of Littorina have partly or entirely calcitic shells. In Pellilitorina the shell is made entirely of calcitic crossed-foliated structure, while in the other two genera there is only an outer calcitic layer of irregular-prismatic structure. A cladistic analysis shows that the calcitic layers have been independently evolved in at least three clades. The calcite is found only in the outermost layers of the shell and in species inhabiting cooler waters of both northern and southern hemispheres. Calcium carbonate is more soluble in cold than warm water and, of the two polymorphs, calcite is about 35% less soluble than aragonite. We suggest that calcitic shell layers are an adaptation of high latitude littorinids to resist shell dissolution.     

Comparative morphometric study of the invasive pearl oyster <Emphasis Type="Italic">Pinctada radiata</Emphasis> along the Tunisian coastline

In order to study the relative growth of the pearl oyster Pinctada radiata in Tunisia, a total of 330 individuals of this species were collected from six sites along the Tunisian coastline. Quantitative measurements of collected oysters were conducted for shell height, shell length, shell width, hinge length, height and width of the nacreous part and wet weight. The size structure of the sampled populations was described and the relative growth between different morphometric characteristics was estimated as allometric growth lines for the six P. radiata samples. It appeared that the majority of examined samples were dominated by large individuals that exceed a shell height of 42 mm. The maximum size (100.5 mm), recorded in Bizerta lagoon, is bigger than that recorded elsewhere in particular in the Red Sea. Size distribution analysis also showed that the majority of P. radiata samples were dominated by two or more size groups. Differences of allometric regression were found between the examined samples for the tested relationships. Moreover, the Factorial Discriminant Analysis, coupled with Ascending Hierarchic Classification, classified the sub-populations according to geographic locations.     

Crystalline structure,orientation and nucleation of the nacreous tablets in the cephalopod <Emphasis Type="Italic">Nautilus</Emphasis>

The nacreous tablets in the Nautilus shell have similar crystalline structure as the tablets in the gastropod Gibbula shell. Etching with Mutvei’s solution reveals that each tablet is composed of vertical crystalline columns that are structurally similar to the acicular crystallites in the outer spherulitic-prismatic layer of the shell wall. The columns are attached to each other to form numerous vertical crystalline lamellae, oriented parallel to the longitudinal axis of the tablet. It is still unknown whether or not the orientation of the vertical lamellae corresponds to that of the crystallographic a- or b-axis. The orientation of the crystalline lamellae in the adjacent tablets is parallel in some nacreous laminae, but random in other laminae. Similar large variation was found in the nacreous tablets of the gastropod and bivalve shells. The nucleation sites of the nacreous tablets are predominantly situated on the peripheral portion of the upper surface of the preceding tablet, both in the shell wall and septa. The “aragonite-nucleating proteins” in the central portion of the crystal imprints of the organic interlamellar sheets, described by several writers, have therefore a negative correlation with the nucleation sites of the nacreous tablets.     

Structure and composition of the boundary zone between aragonitic crossed lamellar and calcitic prism layers in the shell of Concholepas concholepas (Mollusca,Gastropoda)

Mollusc shells are composed of two or three layers. The main layers are well‐studied, but the structural and chemical changes at their boundaries are usually neglected. A microstructural, mineralogical, and biochemical study of the boundary between the inner crossed lamellar and outer prismatic layers of the shell of Concholepas concholepas showed that this boundary is not an abrupt transition. Localized structural and chemical analyses showed that patches of the inner aragonitic crossed lamellar layer persist within the outer calcitic prismatic layer. Moreover, a thin aragonitic layer with a fibrous structure is visible between the two main layers. A three‐step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms. The changes in the secretory process in the mantle cells responsible for the shell layer succession are irregular and discontinuous.