Which animal is the largest invertebrate ever recorded by mass?

The colossal squid is the largest invertebrate ever recorded by mass.

Colossal squid live in the deep Southern Ocean and are known scientifically as Mesonychoteuthis hamiltoni. They have a massive body, swiveling hooks on their tentacles, and eyes among the largest of any animal. Unlike the more slender giant squid, colossal squid are built for bulk rather than extreme length.

The species was described from a fragment in 1925, but intact specimens were not observed until much later. In 2007, a fishing vessel landed a largely intact individual weighing about 495 kilograms, providing the strongest evidence for its exceptional size.

“Largest” depends on the measurement. Giant squid may exceed colossal squid in length, while the colossal squid leads in documented mass. Both are cephalopods, but neither is a true fish; they are molluscs related to octopuses and cuttlefish.