Environmental and Biological Controls on Bivalve Shell Mineralogy

Abstract

Summary Bivalves lay down two forms of calcium carbonate in their shells, aragonite and calcite. Shells may be wholly aragonitic, or may contain both aragonite and calcite, in separate monomineralic layers. Shells are built up of several layers of distinct aggregations of calcium carbonate crystals. These aggregations are referred to as shell structures and their general features are described. Aragonite occurs as prismatic, nacreous, crossed‐lamellar, complex crossed‐lamellar and homogeneous structures. Calcite occurs as prismatic or foliated structures. Myostracal layers (calcium carbonate laid down below sites of muscle attachment) are always aragonitic. The ligament and byssus when calcined are also invariably aragonitic. A summary of the occurrence of calcite and aragonite and the associated shell structures is given. Calcite is found only in the outer layer of superfamilies belonging to the subclass Pterio‐morphia with the exception of two species only from the Heterodont superfamily Chamacea. Generally within a superfamily shell structure and mineralogy are very constant. In all superfamilies these combinations have existed for many millions of years. It is therefore demonstrated that the prime control on shell mineralogy is genetic. Possible controls on mineralogy by the mantle cells, nature of the extrapallial fluid, nature of the periostracum and the organic matrix of the shell layers are discussed. It is known that environmental factors may modify the basic mineralogy/shell structure pattern within a superfamily. Thus there is an inverse relationship between the percentage of calcite in the shell and the mean temperature of the environment inhabited by the bivalve. A critical examination of published data shows that the evidence is convincing only in the superfamily Mytilacea. The species Mytilus californianus, which shows the greatest temperature effects, is peculiar amongst the Mytilacea in having an inner calcite layer as well as an outer one. Conflicting evidence for an inverse relationship between salinity and aragonite content is reviewed. The differences of opinion cannot be resolved without experimental work. We are grateful to the following for much useful discussion, and encouragement in many ways: Dr J. R. Baker, Dr G. E. Beedham, Dr B. C. M. Butler, Dr A. Hallam, Dr J. D. Hudson, Dr R. P. S. Jefferies, Mr J. Macrae, Dr W. S. McKerrow, Mr N. J. Morris, Mr C. P. Palmer, Mr N. Tebble, Dr E. R. Trueman and Professor A. Williams. Our best thanks are to Mr R. Cleevley for critically reviewing the manuscript. The following have rendered us considerable technical assistance: the staff of the electromicroscopy unit of the British Museum (Natural History), under the direction of Mr B. Martin; the technical staff of the Department of Geology, King's College, London and of the Department of Geology and Mineralogy, Oxford; Mrs J. M. Hall, and Mr G. Burton.

Trace elements in bivalve shells from the Río Cruces, Chile

“…Only those metals exhibiting significant patterns or anomalies will be discussed herein. Bivalve shells from time to time may contain small inclusions of foreign matter (Kennedy et al 1969), so peaks that were primarily driven by 1 or 2 data points are not considered to be significant. The results of parallel scans run on the same shell (Fig.…”

Foraminifera promote calcification by elevating their intracellular pH

“…Some groups precipitate predominantly aragonite, such as scleractinian corals (1) and calcareous chlorophytes (2), others mostly calcite, such as foraminifera (3), coccolithophores (4), and corraline Rhodophytes (2), and some a chimera of the two (5,6). The geological prevalence of the different groups is thought to be caused by successions in sea water chemistry: periods with relatively high Ca 2ϩ concentrations and low Mg 2ϩ concentrations (i.e., with low Mg/Ca ratios) have favored organisms precipitating calcite, while periods with relatively high Mg/Ca ratios (e.g., during the Neogene) have favored those forming aragonite (7)(8)(9).…”

Unusual Crystal Formation in Organisms - Exceptions that Confirm Biomineralization Rules

“…Another unusual and unexpected mineral phase, SiCa 2 , was registered only in Zospeum isselianum shells. It is well established that mineralogy and composition of the calcified structure reflect endogenous and exogenous condition in the environment (Dodd, 1967;Kennedy et al, 1969;Carriker et al, 1991). Fritz et al, (1990) indicated that minerals of elemental composition similar to calcium carbonates could be mineralized by mollusks.…”