Gigantidas gladius is a species of large, deepwater, hydrothermal vent mussel, a marine bivalve mollusc in the family Mytilidae, or mussels.
These mussels are found around deep-sea hydrothermal vents on the southern Kermadec Ridge, New Zealand. They form dense beds in these sites.
The shells of this species are up to 30 cm long.
