A belemnite was a sea-dwelling animal that looked like a cuttlefish or squid. In the picture above you can see the fossil remains of a belemnite, which looks something like a bullet. In the video below you can see a polished sample. In the video you can see the shell with its chambers. That is what makes it similar to cuttlefish and ammonites. But in this case the shell was inside. It is, however, not a skeleton.