We present the first record of the very large deep-sea mytilid Gigantidas horikoshii Hashimoto & Yamane, 2005 outside of its type distribution, based on a juvenile specimen collected by fishermen at the Tashi fishing grounds east of Taiwan. This record extends the distribution of the species in about 20 latitudinal degrees to the west (about 1916 km), and it is the first record for this species outside the Izu-Ogasawara Island-arc, southern Japan, representing the westernmost geographic limit of this species and the first record in Taiwanese waters.
