The whole of the body of the Squid is edible, except the beak and gladius (the hard internal part also known as the pen). 

The body can be stuffed whole, cut into pieces or sliced into rings, as with the classic calamari. 

One of the most commercially available species of squid is Ilex Argentinus. 

Cooked well and with care, squid can be meltingly tender and entirely delicious; overcooking makes it rubbery.