explanations have been proposed. In 1902, prior to the development of plate tectonics, Arnold Edward Ortmann proposed that land bridges formerly connected the Seychelles to other land masses. It has also been suggested that the ancestors of Deckenia and Seychellum lived on a landmass comprising Seychelles and the African mainland, which then separated by continental drift; Gondwana is believed to have split up , with the Seychelles separating from the Indian Plate around . An ancient origin would be supported by the absence of freshwater crabs from oceanic islands in the same area, such as Mauritius and Réunion. Finally, the ancestor of Seychellum may have travelled across the western Indian Ocean by rafting, perhaps at a time when the Seychelles Bank was larger due to lower sea levels. The greater extent of the Seychelles Bank may also explain how the species is now found on four separate islands in the Seychelles archipelago. The time of divergence between Seychellum and Deckenia has been estimated independently at and . Seychellum is reported to be more tolerant of salt water than other families of freshwater crabs, which may have allowed it to survive rafting between the African continent and the Seychelles Bank. The most recent research favours trans-oceanic dispersal, but some uncertainty remains. Conservation status Of the five criteria assessed by the International Union for Conservation of Nature for its IUCN Red List, four cannot be assessed in Seychellum alluaudi because of a lack of information. Under the remaining criterion, which measures the species' geographic range, the species would qualify as Endangered if there were was a "decline in habitat quality". It is, however, abundant in places, and is present within a protected area, and is therefore listed as Vulnerable. References External links – includes a photograph of Seychellum Potamoidea Monotypic arthropod genera Fauna of Seychelles Endemic fauna of Seychelles Crustaceans described in 1893