Giant Squid have an average length in the region of 3-9 metres, however specimens of 13 metres have been found. They have a mass of 445kg on average but can weigh up to 1000kg.
Adaptations
Giant squid require a very efficient gas exchange, this is accomplished through an number of adaptations. As mentioned before the respiratory pigment haemocyanin allows for oxygen to be carried in the blood, there is also capillary circulation in the gills which allows for more gas to be exchanged due to the higher surface area.
Comparison to human respiratory system
The two systems are different mainly because a squid obtains oxygen through water that contains 30 times less oxygen than the same volume of air. Therefore water flow through the squid is constant whereas air only enters the lungs when we inhale. The gill therefore is designed differently to the lung. The gill has hierarchical structure due to the amount of oxygen that is required, the longer the structure and therefore the larger the surface area, they are shaped a slits so to allow and constant flow of water through the system. Lungs also have a hierarchical structure although getting smaller rather than getting larger with the decrease in size of the divisions.
Sources
https://prezi.com/xhv7vr81nui0/giant-squidrespiratory-system/
http://marinebio.org/species.asp?id=156
Image:http: //www.exploringnature.org/db/view/570
http://www.nrcresearchpress.com/doi/abs/10.1139/f82-082#.VoZpW7iyOkp
https://books.google.co.uk/books?id=zuT5z5cPWhcC&pg=PA16&lpg=PA16&dq=cephalopod+respiratory+system+adaptations&source=bl&ots=MIgrN6k9DT&sig=fYpej5z1SEkQTiucT74LUiToNKE&hl=en&sa=X&ved=0ahUKEwi1kL-MhovKAhXL1xQKHWASD-EQ6AEILjAD#v=onepage&q=cephalopod%20respiratory%20system%20adaptations&f=false