Nature's conveyor belt - the matrix mediated biomineralization of magnetite in chitons (Mollusca)

Chitons are marine molluscs that use a variety of iron and calcium based minerals to harden their teeth, which they use to scrape algae growing upon, and within, rocks. The teeth are mounted on a long ribbon-like organ termed the radula, with immature, unmineralized teeth at the posterior end and the hardened iron-mineralized teeth at the anterior end (Fig. 1). At any one time, up to 80 individual tooth rows can be observed, with each row becoming progressively mineralized as it moves forward in a conveyor belt-like manner. The ability to study the entire mineralization process in a single animal makes these creatures ideal for the study of matrix mediated biomineralization. The chiton’s ability to mineralize iron has inspired researchers who believe that new biomimetic materials and technologies can be developed based on the principles of biomineral formation

Does nature conservation enhance ecosystem services delivery?

Whilst a number of studies have examined the effects of biodiversity conservation on the delivery of ecosystems, they have been often limited by the scope of the ecosystem services (ES) assessed and often suffer from confounding spatial issues. This paper examines the impacts of nature conservation (designation) on the delivery of a full suite of ES across nine case-studies in the UK, using expert opinion. The case-studies covered a range of habitats and explore the delivery of ES from a ‘protected site’ and a comparable ‘non-protected’ site. By conducting pair-wise comparisons between comparable sites our study is one of the first to attempt to mitigate confounding cause and effect factors in relation to spatial context in correlative studies. Protected sites delivered higher levels of ecosystem services than nonprotected sites, with the main differences being in the cultural and regulating ecosystem services. Against expectations, there was no consistent negative impact of protection on provisioning services across the case-studies. Whilst the analysis demonstrated general patterns and differences in ecosystem delivery between protected and non-protected sites, the individual responses in each case-study highlights the importance of the social, biophysical, economic and temporal context of individual protected areas and the associated management

Radula synthesis by three species of iron mineralizing molluscs: production rate and elemental demand

A cold-shock technique was used to determine radula production rates for the chitons Acanthopleura hirtosa and Plaxiphora albida, and for the limpet Patelloida alticostata, which replaced their radular teeth at rates of 0.40, 0.36 and 0.51 rows d-1, respectively. These rates are far slower than those determined previously for non-iron-mineralizing molluscs, suggesting that the improved working life of the teeth afforded by iron-mineralization acts to significantly reduce replacement rates. In addition, inductively coupled plasma-atomic emission spectroscopy has been used to determine the quantity of iron and other elements comprising the radula of each species. These data, used in conjunction with the radula production rates, reveal that A. hirtosa, Plaxiphora albida and Patelloida alticostata have daily radula mineralization requirements for iron of 3.06, 4.12 and 0.55 μg, respectively. Such information is vital for continuing studies related to the cellular delivery of ions and subsequent biomineralization of the tooth cusps in chitons and limpets

Ultrastructure of the epithelial cells associated with tooth biomineralization in the chiton Acanthopleura hirtosa

The cusp epithelium is a specialized branch of the superior epithelium that surrounds the developing teeth of chitons and is responsible for delivering the elements required for the formation of biominerals within the major lateral teeth. These biominerals are deposited within specific regions of the tooth in sequence, making it possible to conduct a row by row examination of cell development in the cusp epithelium as the teeth progress from the unmineralized to the mineralized state. Cusp epithelium from the chiton Acanthopleura hirtosa was prepared using conventional chemical and microwave assisted tissue processing, for observation by light microscopy, conventional transmission electron microscopy (TEM) and energy filtered TEM. The onset of iron mineralization within the teeth, initiated at row 13, is associated with a number of dramatic changes in the ultrastructure of the apical cusp cell epithelium. Specifically, the presence of ferritin containing siderosomes, the position and number of mitochondria, and the structure of the cell microvilli are each linked to aspects of the mineralization process. These changes in tissue development are discussed in context with their influence over the physiological conditions within both the cells and extracellular compartment of the tooth at the onset of iron mineralization

Biomineralization in chiton teeth and its usefulness as a taxonomic character in the genus Acanthopleura Guilding, 1829 (Mollusca: Polyplacophora)

The physical structure and mechanisms of biomineralizatìon have been elucidated in the major lateral teeth of the chiton genus Acanthopleura with the aid of light and scanning electron microscopy and energy dispersive spectroscopy. Following its recent revision, this genus currently consists of 15 species, including three species suppressed as synonyms. Specimens representing all 18 (nominal) species have been examined. With two exceptions, the major laterals are typically discoid and unicuspid with only limited interspecific variation. The teeth of A. loochooana are also essentially discoid but have a small, distinct distal indentation, while those of A. rehderi possess four short rounded denticles. Biomineralization in all species of Acanlhopleura occurs in architecturally discrete compartments and, with the exception of A. rehderi, is consistent in all tooth regions except the cusp core, where A. curtisiana, A. miles, A. araucariana and A. loochooana differ in having substantial amounts of iron. The first three of these species were previously included in the genus Squamopleura and there is evidence to suggest that this genus should not have been suppressed. The substantial difference in tooth structure between A. rehderi, with its four denticles and total lack of a lepidocrocite region, and that of other members of the genus Acanthopleura suggest that this species may be more closely aligned with Onithochiton. The inclusion of additional characters, such as tooth biomineralization, is strongly recommended in future studies of chiton taxonomy

In situ studies of biomineral deposition in the radula teeth of chitons of the suborder chitonina

The major lateral radula teeth of chitons (Mollusca: Polyplacophora) are composite materials, incorporating a variety of biominerals within an organic scaffold. While magnetite is ubiquitous to these teeth in all Polyplacophorans whose radulae have been described to date, this is not the case for the biominerals of the tooth core. In situ analsysis, using energy dispersive spectroscopy, to determine the distribution of elements in chiton teeth, and Raman spectroscopy, to identify the biominerals present, has been undertaken in the mature teeth of seven chiton species representing three families in the suborder Chitonina. The results show the tooth core to be comprised of a variety of elements, with the main biominerals identified as limonite, lepidocrocite and hydroxyapatite. Along with Ischnochiton australis, all five representatives of the Chitonidae deposit an apatitic mineral in their tooth core, while Plaxiphora albida does not deposit any calcium biomineral. With the exception of Acanthopleura echinata, the hydrated iron (III) oxide, limonite, is found in all species, including I. australis, which has relatively small amounts of iron in its tooth core. The lack of any evidence for a phosphate mineral in species that possess high levels of phosphorus in their core, challenges the long accepted notion that the presence of phosphorus implies its deposition as a biomineral. The combined techniques of energy dispersive spectroscopy and Raman spectroscopy provide a simple and effective means to evaluate, in situ, the biomineralisation strategies employed by chitons. While the results from this study are inconclusive in determining whether biomineralisation strategies reflect phylogenetic affinities in chitons, an extension of the study to include a wider range of chiton taxa could provide a basis for the utilisation of radula tooth biomineralisation as a systematic tool in this class of molluscs

Radula tooth turnover in the chiton, Acanthopleura hirtosa (Blainville, 1825) (Mollusca : Polyplacophora)

The rate of radula production in the chiton Acanthopleura hirtosa (Blainville, 1825) was determined by following structural irregularities induced in the radula using a cold-shock treatment of 4°C for 48 h. In animals treated in this manner and subsequently maintained in an artificial intertidal habitat to ensure, as far as possible, a natural feeding regimen, the rate of radular production was calculated as 0.36 rows per day. This indicates that A. hirtosa renews its total radular length (mean 78 rows, SD = 6.5, n = 23) approximately once every 6.5 months, a relatively slow rate when compared with that of other molluscs

Structure and synthesis of biominerals in chiton teeth.

The structure and organisation of the organic matrix of the cusps of the major lateral teeth of chitons have been examined using conventional and light microscopy in two species, Acanthopleura hirtosa and Plaxiphora albida. The results show that the organisation of the matrix differs between different regions of individual cusps. In addition, there are considerable differences in matrix structure of the same region between the two species. This is particularly so in the case of the transition zone that separates the posterior and anterior compartments of the teeth and which, in A. hirtosa, would appear to be the major factor limiting ion flow between them. The structure of the matrix at the surface is also different to that in the rest of the tooth, presumably in order to toughen the cutting surfac