CaCO 3 content is significantly lower. In habitats with low calcium content they
cannot construct fully calcified carapace and the valve may then consist primarily of
chitinous fibres (Keyser and Walter 2004). In low salinity environments ostracods
seem to have less mineralised, mainly chitinous valves, but they still have carapace
to protect their soft body parts.
The ostracod carapace is shed by moulting up to eight times during development
and each stage has new and more heavily calcified valves. In ostracods the calcite is
not reabsorbed from the old carapace during moulting, as happens in many malacostracan crustaceans, but is removed and formed again during calcification of the
new valves (Turpen and Angell 1971; Keyser and Walter 2004). Prior to moulting
ostracods begin producing the carapace by the absorption of a large amount of
calcium compounds and chitin precursors. The uncalcified inner lamella cuticle is
formed by the inner epidermal cells (Yamada and Keyser 2010). The outer epidermal layer beneath the calcified cuticle contains large amounts of granules within
the cells. These intracellular bodies contain compounds of calcium phosphate and
small amounts of sodium, potassium, chloride and sulphur. Neither magnesium nor
strontium (known to be present in the fully calcified carapace) is found in these
granules. In the next step calcium is released from the globules, penetrates the
epidermal membrane and then forms granules of amorphous calcite outside
the membrane. Some species (e.g. C. ophtalmica) retain amorphous calcite in the
carapace, but most transform the calcite into the final crystalline arrangement in the
epidermal layer, because amorphous calcite dissolves easily. In the juvenile stages
crystallisation is not complete and the organisms have weaker shells. This mechanism is similar for both marine and freshwater ostracods (Turpen and Angell 1971;
Keyser and Walter 2004; Yamada et al. 2005; Yamada and Keyser 2010).
The chemistry of the ostracod valve is a function of the surrounding water
chemistry modified by temperature, calcification rate, and inter- and intra-specific
variability (Van der Meeren et al. 2011). The influence of salinity levels on ostracod
calcification is unclear. Some authors (e.g. De Deckker et al. 1999) found no
relationship between Mg/Ca content of the ostracod valve and salinity, while others
(e.g. Chivas et al. 1986) found a positive correlation between salinity and Mg/Ca
content in the carapace. Decrouy et al. (2011) noticed that in shallow waters higher
temperatures increased the Mg/Ca and DIC concentration of water, which may have
an effect on ostracod mineralisation. Additionally, Carbonel et al. (1988) suggested
that the structure, ornamentation and size of the carapace may be correlated with the
degree of salinity.
Eleven out of 15 extant orders of Foraminifera precipitate calcareous tests and
thus are among the major producers of calcium carbonate in the oceans (Hansen
2003; Bentov et al. 2009). In pelagic foraminifers the test wall consists of extremely
pure calcite (about 99 % by weight CaCO 3 ) and trace elements such as Mg, Sr, Ba
and Cd. Elements are incorporated directly from ambient sea water during test
precipitation, thus shell composition reflects chemical composition of the medium,
and both physical and biological conditions present during calcification (Lea 2003).
According to test structure calcifying Foraminifera are commonly divided into
two groups: miliolid and hyaline. The miliolid test contains relatively high Mg/Ca
104
A. Iglikowska and J. Pawłowska
cannot construct fully calcified carapace and the valve may then consist primarily of
chitinous fibres (Keyser and Walter 2004). In low salinity environments ostracods
seem to have less mineralised, mainly chitinous valves, but they still have carapace
to protect their soft body parts.
The ostracod carapace is shed by moulting up to eight times during development
and each stage has new and more heavily calcified valves. In ostracods the calcite is
not reabsorbed from the old carapace during moulting, as happens in many malacostracan crustaceans, but is removed and formed again during calcification of the
new valves (Turpen and Angell 1971; Keyser and Walter 2004). Prior to moulting
ostracods begin producing the carapace by the absorption of a large amount of
calcium compounds and chitin precursors. The uncalcified inner lamella cuticle is
formed by the inner epidermal cells (Yamada and Keyser 2010). The outer epidermal layer beneath the calcified cuticle contains large amounts of granules within
the cells. These intracellular bodies contain compounds of calcium phosphate and
small amounts of sodium, potassium, chloride and sulphur. Neither magnesium nor
strontium (known to be present in the fully calcified carapace) is found in these
granules. In the next step calcium is released from the globules, penetrates the
epidermal membrane and then forms granules of amorphous calcite outside
the membrane. Some species (e.g. C. ophtalmica) retain amorphous calcite in the
carapace, but most transform the calcite into the final crystalline arrangement in the
epidermal layer, because amorphous calcite dissolves easily. In the juvenile stages
crystallisation is not complete and the organisms have weaker shells. This mechanism is similar for both marine and freshwater ostracods (Turpen and Angell 1971;
Keyser and Walter 2004; Yamada et al. 2005; Yamada and Keyser 2010).
The chemistry of the ostracod valve is a function of the surrounding water
chemistry modified by temperature, calcification rate, and inter- and intra-specific
variability (Van der Meeren et al. 2011). The influence of salinity levels on ostracod
calcification is unclear. Some authors (e.g. De Deckker et al. 1999) found no
relationship between Mg/Ca content of the ostracod valve and salinity, while others
(e.g. Chivas et al. 1986) found a positive correlation between salinity and Mg/Ca
content in the carapace. Decrouy et al. (2011) noticed that in shallow waters higher
temperatures increased the Mg/Ca and DIC concentration of water, which may have
an effect on ostracod mineralisation. Additionally, Carbonel et al. (1988) suggested
that the structure, ornamentation and size of the carapace may be correlated with the
degree of salinity.
Eleven out of 15 extant orders of Foraminifera precipitate calcareous tests and
thus are among the major producers of calcium carbonate in the oceans (Hansen
2003; Bentov et al. 2009). In pelagic foraminifers the test wall consists of extremely
pure calcite (about 99 % by weight CaCO 3 ) and trace elements such as Mg, Sr, Ba
and Cd. Elements are incorporated directly from ambient sea water during test
precipitation, thus shell composition reflects chemical composition of the medium,
and both physical and biological conditions present during calcification (Lea 2003).
According to test structure calcifying Foraminifera are commonly divided into
two groups: miliolid and hyaline. The miliolid test contains relatively high Mg/Ca
104
A. Iglikowska and J. Pawłowska