Belemnitida
Videos
Belemnitida is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are
Reconstruction of the belemnite Passaloteuthis
The Jurassic Youngibelus reconstructed with hectocotyli
Cephalopod embryonic shells. A) Ammonoidea (B) Sepiida (C) Belemnoidea (D) Spirulida (E) Orthocerida (F) Nautilida (G) Oncocerida (H) Pseudorthocerida (I) Oegopsina (J) Bactritida. IC indicates the initial chamber.
Siphuncle
Videos
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnit
A shell of Nautilus pompilius in cross section. Septal necks are preserved, but the thin connecting rings have been degraded and lost.
These polished orthocerid nautiloid cephalopod fossils from Morocco have fully preserved septal necks and connecting rings outlining the shape of the siphuncle.