Biogeography
The presence of Astacoides on the island of Madagascar is difficult to explain. The other members of the family Parastacidae are found in South America and Australasia, suggesting a Gondwanan origin for the family. However, there are no native crayfish in either Africa or India, the two landmasses with the most recent connections to Madagascar in the geological past. The genus which shares the greatest similarities with Astacoides is the Tasmanian genus Astacopsis. Given the large distance between Tasmania and Madagascar, it has been suggested that although the freshwater crayfish are a monophyletic group, their common ancestor may have lived in the seas, with separate crayfish lineages colonising the rivers separately.
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