ETRURIA. Pisae. 4th-3rd century BC. Diobol (Silver, 11 mm, 1.05 g). Six-armed octopus; around, raised circular border. Rev. Blank. HN III 227. Vecchi EC 5.30 (this coin). Very rare. Dark toning. Good very fine.
From the "Collection sans Pareille" of Ancient Greek Fractions and that of Leo Mildenberg, ex Monnaies et Médailles 52, 19 June 1975, 4.
Why does this 'octopus' have only six arms? Could it be that there were octopi in Pisae (modern Pisa, on the Arno where it meets the Ligurian Sea) which only had six? Or, more likely, is it that the engraver sacrificed accuracy for practicality!