The body of the colossal squid

A colossal squid has three main body parts: the mantle and fin, the head, and a circle of arms and tentacles.

The mantle

The main body of the squid is called the mantle, which fits like a sheath over the internal organs. This colossal squid's mantle is about 2.5 metres long and about 982 millimetres wide, almost the same diameter as a truck tyre.+

The mantle is made up of muscle and skin. Small pigment-containing cells, called chromatophores, give the skin its reddish-pink colour. When these cells contract, the skin appears paler. The reddish skin of the colossal squid in the tank is peeling off the mantle surface in some places.

When the squid was caught and still alive, it was bright red, which may be a sign that it was under stress.

Colossal squid Mesonychoteuthis hamiltoni Robson, photographed from above

Caption

Colossal squid, Mesonychoteuthis hamiltoni Robson, 1925, collected 2008, Ross Sea, Antarctica. Gift of the Ministry of Fisheries, 2007. CC BY-NC-ND licence. Te Papa (M.190318)

Gladius, or pen

All molluscs have a shell. The colossal squid has an internal shell called the gladius. The gladius is a rigid internal structure that supports the squid's body and runs through the upper part of the mantle, between the paired tail fin. It is made of chitin – a tough, protective, and semi-transparent substance, which is primarily a nitrogen-containing polysaccharide. The gladius is easy to remove when dissecting a squid, and looks like a long piece of plastic.

Tail fin

The paired tail fin is attached to the upper surface of the mantle and is made up of muscle. The colossal squid swims forward through the water by undulating the fin longitudinally.

The fin is unusually massive and muscular (1,183 millimetres long and 982 millimetres wide). This probably enables the colossal squid to move forward quite rapidly in short bursts when attacking prey. In most squid, the paired tail fins are used more for changing direction than propulsion.

Funnel or siphon

The funnel, or siphon, is a muscular structure located on the ventral surface of the mantle. It has several functions, including respiration and discharge of wastes. The colossal squid also uses the funnel to help it move in the water.

When the mantle expands, water is sucked into the squid's mantle cavity through the mantle opening around the head. Oxygenated water then bathes the gills for respiration.

When the mantle contracts, water is squirted out through the funnel along with waste products. The squid can move backwards using jet propulsion by rapidly shooting water out through the funnel.