Strabo mistook the fossil shells in the pyramids for workers' leftover lentils
In the 1st century BCE the geographer Strabo noticed coin-like objects packed into the stone of the Great Pyramid and guessed they were petrified lentils dropped by the builders. They were actually shells of Nummulites, single-celled organisms called foraminifera, some of which build homes up to 20 centimetres across.
Foraminifera, Latin for hole bearers, are amoeba-like protists that mostly live in the sea, crawling through seafloor mud or drifting as plankton; a few turn up in fresh water and even soil. Around 50,000 species are recognised, roughly 40,000 of them fossils. Most are under a millimetre, but giants reach 20 centimetres. Their shells, called tests, can be made of chitin, protein, calcium carbonate or glued sediment grains, and one uses silica. Unusually, the shell sits inside the cell membrane rather than outside it.
Pores in the test let out a web of thread-like pseudopods in which granules stream both ways. These threads split and rejoin, and the cell assembles and dismantles internal scaffolding quickly to extend or retract them. They serve for moving, anchoring, building the shell and catching prey, from bacteria and diatoms to small crustaceans; some forams drill into the shells of other forams. Many host algae as internal partners, and some steal chloroplasts from their food to photosynthesise. A few are parasites of sponges, molluscs or corals, and certain deep-sea giants called xenophyophores hold some of the highest concentrations of radioactive isotopes of any complex cell, for reasons unknown.
Scientists took centuries to work out what they were. Robert Hooke described one in Micrographia in 1665 as resembling a tiny water-snail shell, and Antonie van Leeuwenhoek called them minute cockles in 1700. Early naturalists filed them with the nautilus. In 1826 Alcide d'Orbigny named them hole-bearers but still treated them as miniature cephalopods, reading the pseudopods as tentacles. Only in 1835 did Felix Dujardin recognise them as single-celled.
Classification swung from shell shape to wall composition to the fine structure of the test wall, the basis of Tappan and Loeblich's 1964 scheme that molecular studies have largely confirmed. The geologist Irene Crespin published some ninety sole-authored papers, including notable foram research. Genetics places the group in the Rhizaria, alongside radiolarians.
Source: Foraminifera
