What is the largest invertebrate?

The colossal squid is the largest known invertebrate, especially when measured by mass. Its scientific name is Mesonychoteuthis hamiltoni, and it lives in the cold, deep waters of the Southern Ocean around Antarctica.

The species is confirmed to reach at least 495 kilograms. That record comes from a female caught in the Ross Sea in 2007 and later studied at New Zealand’s Museum of New Zealand Te Papa Tongarewa. Even larger animals may exist: enormous beaks recovered from sperm-whale stomachs suggest that some colossal squid exceed the size of the best-preserved specimens.

The giant squid is the main source of confusion. It may be longer overall because of its extended feeding tentacles, but the colossal squid is heavier and has the greater confirmed mass. Length estimates for both species can be misleading because tentacles stretch, contract or are measured differently after death.

Colossal squid are ambush predators with swivelling hooks on their arms and tentacles. They also have exceptionally large eyes, an adaptation that may help them detect prey and predators in the dim deep ocean.