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What materials make up the shells of articulate lamp shells?
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lamp shells
Lamp shells on the sea floor off the coast of Massachusetts.
The shells of articulate lamp shells (class Articulata) are always calcareous and are composed of three distinct layers.12
- Outer layer: Known as the periostracum, this layer is made of an organic substance and is rarely preserved in fossils.2
- Middle layer: This layer consists of calcium carbonate in the form of calcite.2
- Inner layer: This layer is also composed of calcite fibres. Depending on the specific type of articulate brachiopod, this inner layer may be:2
- Punctate: Perforated by minute pits.2
- Pseudopunctate: Containing vertical rods of calcite known as taleolae.2
- Impunctate: Lacking both pits and taleolae.2