Fossil Record
Although the fossil record of pycnogonids is scant, it is clear that they once possessed a coelom, but it was later lost, and that the group is very old.
The earliest fossils are known from the Cambrian 'Orsten' of Sweden, the Silurian Wenlock Series of England and the Devonian Hunsrück Slate of Germany. Some of these specimens are significant in that they possess a longer 'trunk' behind the abdomen and in two fossils the body ends in a tail; something never seen in living sea spiders.
In 2007 remarkably well preserved fossils were exposed in fossil beds at La Voulte-sur-Rhône, south of Lyon in south-eastern France. Researchers from the University of Lyon discovered about 70 fossils from three distinct species in the 160 million-year-old Jurassic La Voulte Lagerstätte. The find will help fill in an enormous gap in the history of these creatures.
Read more about this topic: Sea Spider
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