Thysanoteuthis rhombus, also known as the diamond squid or diamondback squid, is a large species of squid growing to 100 cm in mantle length and a maximum weight of 30 kg, although it averages around 20 kg. The species occurs worldwide, throughout tropical and subtropical waters. Arms have two series of suckers, whereas the tentacular clubs have four. It lacks photophores. T. rhombus is named for its fins, which run in equal length along the mantle, giving the appearance of a rhombus. The species is commercially fished in Japan, specifically in the Sea of Japan and Okinawa.