The beak of the colossal squid
Like all squid and octopus, and their relatives, the colossal squid has a beak. This is essentially the mouth of the squid, and the first stage of the digestive system.
The beak is a hard structure rather like a parrot's beak. However, unlike a parrot's beak, the lower beak of the colossal squid overlaps the upper beak. The beak is made of chitin and is surrounded by muscular tissue.
The colossal squid uses its beak to chop and slice up prey before the food is passed down the oesophagus into the stomach and digestive organs. The squid has to reduce the food to smaller chunks because its oesophagus is narrow and passes through the middle of the squid's doughnut-shaped brain.
Inside the beak, just before the start of the oesophagus, the food is shredded up further by the radula, which is rather like a tongue with teeth. Further teeth (palatine teeth) line the cheeks (palatine palps). The radula moves like a conveyor belt to shunt food down the oesophagus as it is processed by the beak.
Squid beak and size
Each squid species has a beak that is unique in size and shape. The size of a squid beak is related to the size of the living animal. The measurement used is the length of the straight cutting section of the lower beak, called the lower rostral length (LRL). Given enough specimens of a squid species, it is possible to work out a mathematical relationship between the size of the beak and the overall size of the squid.
Colossal squid and other large squid are rarely captured, so there are only a few large specimens in collections. Sperm whales eat many colossal squid. While squid tissue dissolves very quickly in the stomach juices of the whale, the hard squid beaks are left behind. Large numbers of colossal squid beaks have been found in the stomach contents of stranded sperm whales. The largest colossal squid beak found in a sperm whale stomach had an LRL of 49 millimetres.
During the colossal squid examination at Te Papa, a smaller colossal squid was dissected and the beak removed while the scientists waited for the larger colossal squid to thaw in the tank. This smaller specimen weighs about 160 kilogrammes and has a beak LRL of about 40 millimetres. The larger colossal squid specimen weighs 495 kilogrammes and has a beak LRL of 42.5 millimetres. So only a few millimetres difference in beak size corresponds with a much bigger squid overall.
There are not enough colossal squid specimens to be able to work out the equation linking beak size and overall size. While we can't say for sure what size colossal squid a 49 millimetre beak length represents, it could be up to a massive 600 or 700 kilograms.