Mollusca · mollusks

Colossal squid

Mesonychoteuthis hamiltoni

Cranchiidae · glass squidsIUCN: Least Concern

The heaviest invertebrate on Earth, with swiveling hooks on its arms.

Fun factThe first footage of a live colossal squid in the wild was taken in 2025.

Waters
Southern Ocean
Depth zone
Twilight zone, 200–1,000 m, Deep sea & continental slope
Diet
Fish such as toothfish
Size
Up to 500 kg

Classification

Mollusca › Cephalopoda › Oegopsida › Cranchiidae

  1. Kingdom Animalia animals
    • Many-celled organisms that eat other living things for energy (heterotrophs)
    • Cells have no cell walls
    • Most can move at some stage of life
  2. Clade Bilateria bilateral animals
    • Body has a left and right side that mirror each other (bilateral symmetry)
    • Head end with concentrated nerves; three tissue layers
    • Includes about 99% of all living animal species
  3. Clade Protostomia protostomes
    • In the embryo, the first opening usually becomes the mouth
    • Main nerve cord runs along the belly (ventral)
    • Includes mollusks, worms, and arthropods
  4. Clade Spiralia mollusks, worms & kin
    • Embryos usually divide in a spiral pattern (spiral cleavage)
    • Many have a swimming larva with a band of cilia (trochophore)
    • Includes mollusks and segmented worms
  5. Phylum Mollusca mollusks
    • Soft body with a muscular foot and a fold of tissue (mantle) that makes the shell
    • Most have a rasping, tongue-like ribbon of teeth (radula)
    • Includes snails, clams, octopuses, and chitons
  6. Class Cephalopoda cephalopods
    • Foot is modified into arms and tentacles around the head
    • Large brains and camera-like eyes
    • Jet propulsion by squirting water through a funnel (siphon)
  7. Subclass Coleoidea octopuses, squids & cuttlefish
    • Shell is internal, reduced, or absent
    • Most have an ink sac and color-changing skin cells (chromatophores)
    • Includes octopuses, squids, and cuttlefish
  8. Superorder Decapodiformes squids & cuttlefish
    • Ten appendages: eight arms plus two longer feeding tentacles
    • Includes squids, cuttlefish, and bobtail squids
  9. Order Oegopsida open-ocean squids
    • Open-ocean squids whose eyes have no covering membrane
    • Many have hooks on their arms or tentacles
  10. Family Cranchiidae glass squids
    • Glass squids: see-through bodies filled with ammonia-rich fluid for buoyancy
    • Includes the colossal squid, the heaviest invertebrate
  11. Genus Mesonychoteuthis
    • Species in the same genus are very close relatives and often look alike.
  12. Species Mesonychoteuthis hamiltoni Colossal squid

Closest relatives in the guide