an order of extinct invertebrate animals of the class Cephalopoda. They lived from the Carboniferous period to the Paleocene. They were externally similar to squids (Teuthoidea), but, in distinction to this latter group, Belemnitida had an internal shell consisting of three parts: the phragmocone, proostracum, and guard. The phragmocone was conical and divided by barriers into chambers, through which ran an outgrowth of the soft body, the siphuncle. The lamellar proostracum was located on the dorsal side of the animal in front of the phragmocone. The guard (up to 40 cm long) was a cigar-shaped or lanceolate body, a sort of sheath covering the phragmocone and usually extending far beyond it. Belemnitida lived in the oceans, leading a predatory way of life; most of the Belemnitida swam well. Because of their wide distribution, abundance of genera (approximately 50) and species, and also their quick changes over time, Belemnitida are the leading fossils for the Jurassic and Cretaceous deposits. Isolated guards of the Belemnitida are known as “devils fingers.”