Orthoceras were ancient molluscs that lived more than 400 million years ago and are mainly found in Europe and North Africa. The name means straight horn, referring to the characteristic long, straight, conical shell. The preserved shell is all that remains of this ancestor of our modern-day squid. Their shells were divided into chambers by internal divisions called septae. The septae and the tube-like siphuncle running the length of the shell can be seen clearly in specimens. Orthoceras were active swimmers, swimming by squirting water out of the body cavity.