noun
Japanese mud crab
A species of crab, Macrophthalmus japonicus, found in mudflats. Typically written in katakana as a biological name.
干潟でヤマトオサガニを見つけた。
I found a Japanese mud crab on the mudflat.
The name combines 大和 (Yamato, an old name for Japan) and 長蟹 (osa-gani, likely referring to a type of crab). The exact derivation of 'osa' is uncertain.