Hi LLTT and

to TONMO!
I'm afraid what you have there is not an octopus tentacle but you are certainly in the right place on a cephalopod site! The fossil is a fragment of a straight shelled ammonite called
Baculites. This was a heteromorph ammonite which grew in a coil in its juvenile stage but developed its long straight shell as it matured.
Baculites, literally "walking stick rock" was a common form of ammonite in the late Cretaceous seas. It grew up to 2 metres long and is thought to have lived in a vertical orientation with the head hanging straight downwards. As there is no counterweight to the head at the apex of a complete shell, researchers believe that this was the only way the animal could have been orientated, so the animal could have swum vertically but probably very poorly, if at all, horizontally.
The animal is one of the youngest ammonites known, ranging from the Turonian to the Maastrichtian of the Cretaceous (i.e 93-65mya) and has a worldwide distribution. In some deposits they are common fossils and are thought to have lived in great shoals. One strange feature about these animals is that it is believed that the males were a third to a half the size of the females and had much lighter ribbing on the surface of the shell.
Nice find! If you know exactly where it came from , I'm sure we can pin-point the date more accurately. Here are two pictures attached of some
Baculites on the seabed from the University of Michigan displays.
Hope that helps and is some interest,
Phil
(By the way, you have posted the same photo twice!)