Sawagani (Geothelphusa dehaani)

Because the crab crawls sideways, never backwards, samurai interpreted the crab as a symbol of bravery. The claws and hard shell of the crab also relate to the iron armor of warriors, who frequently wore fantastic iron helmets in the form of the crab. Since the Edo period (1615–1868), the crab has featured in the jizai work of the Myochin school of metalsmiths up to the pioneer of articulated sculpture in the modern period, Takase Kozan (1868–1894).
Though most jizai crabs are of the small, freshwater variety (sawagani), there are rarer examples of swimming crabs (watarigani), such as one in the British Museum. The smallest known articulated crab with 0.8 cm shell is in the Kiyomizu Sannenzaka Museum, Kyoto.
In Mandarin Chinese, crab is pronounced xie, a homophone for “harmony” 諧. As the shell of the crab means both “armor”, jia, and “first”, the crab also connotes success in the civil examination required for advancement.