Genetic differences between two spider crabs Pisoides bidentatus (A. Milne-Edwards, 1873) and Pugettia quadridens (de Haan, 1839) (Decapoda: Brachyura: Majoidea) from the Sea of Japan

Biochemical genetics was applied to elucidate the taxonomic position of the spider crab Pisoides bidentatus. Two morphologically similar spider crabs, P. bidentatus and Pugettia quadridens, were compared with four sympatric brachyuran species, Eriocheir japonicus, Hemigrapsus sanguineus, Hemigrapsus penicillatus (Varunidae), and Cancer amphioetus (Cancridae), using 20 allozyme loci. High genetic identity-value between P. bidentatus and P. quadridens (I = 0.758 ± 0.092) suggests that they should evidently be placed to one genus. This conclusion is supported by the similar identity-value between two species of the genus Hemigrapsus (I = 0.821 ± 0.078) and the low genetic similarity (I = 0.125 ± 0.05) between different genera, Hemigrapsus and Eriocheir, within the family Varunidae.