Gigantidas horikoshi is a species of large, deepwater, hydrothermal vent mussel, a marine bivalve mollusc in the family Mytilidae, the mussels.
Shell size 160-170 mm.
694 m. depth: Sumisu Caldera hydrothermal vent field
(31°28.2113'N, 140°4.2833'E), Izu Islands arc, Japan.