How big are cephalopods?

Cephalopods include the largest invertebrates in the world and have a wide range of sizes from very small cuttlefish to the giant and colossal squid that inhabit the deep ocean.  In fact, the size of the giant and colossal squid is truly amazing.  The confirmed size, as seen by examining a dead specimen, is as big as 18 m (50 feet).  However, by measuring the size of sucker marks on the heads of sperm whales and by the size of some of the beaks found in the stomach of these whales, there are very likely much larger specimens swimming in the depths of the ocean.