Behavioural and Molecular Evidence for the Systematic Position of Macrophthalmus (hemiplax) Hirtipes Hombron & Jacquinot, 1846, with Comments on Macrophthalmine Subgenera (decapoda, Brachyura, Macrophthalmidae)

The analysis of 16s rRNA data from the New Zealand sentinel crab, Macrophthalmus (Hemiplax) hirtipes (Jacquinot & Hombron, 1846) (Macrophthalminae: Macrophthalmidae) shows that it is the most basal species in the genus Macrophthalmus, and behavioural trait mapping suggests that ancestral behaviours included extended cheliped fighting. Other behaviour found in some sentinel crabs, such as allocleaning and waving displays, were absent in the ancestor and are regarded here as derived traits. It is proposed that the two subgenera Hemiplax and Tasmanoplax be elevated to full generic status. Three subgenera appear to be polyphyletic: Macrophthalmus (26 species), Mareotis (14 species) and Paramareotis (4 species), and to resolve this problem molecular data from the remaining species will need to be added into the analysis. The Australasian fauna contains the four most basal genera of the Macrophthalminae: Tasmanoplax, Hemiplax, Australoplax, and Enigmaplax. Our hypothesis is that these were early off-shoots from Tethyan ancestor(s) that colonized Australasia.