Gladius (cephalopod)


The gladius, or pen, is a hard internal bodypart found in many cephalopods of the superorder Decapodiformes and in a single extant member of the Octopodiformes, the vampire squid. It is so named for its superficial resemblance to the Roman short sword of the same name, and is a vestige of the ancestral mollusc shell, which was external. The gladius is located dorsally within the mantle and usually extends for its entire length. Composed primarily of chitin, it lies within the shell sac, which is responsible for its secretion. Some species, like the bigfin reef squid, still has a gladius with some degree of mineralization.
Gladii are known from a number of extinct cephalopod groups, including teudopseids, loligosepiids, and prototeuthids.

Morphology

Gladii are shaped in many distinctive ways and vary considerably between species, though are often like a feather or leaf. The equivalent part in cuttlefish is the cuttlebone. Below are examples of gladii from various families of squid;
Shape of gladiusSpeciesFamily
Ancistroteuthis lichtensteiniOnychoteuthidae
Architeuthis sp.Architeuthidae
Bathyteuthis abyssicolaBathyteuthidae
Histioteuthis bonnelliiHistioteuthidae
Histioteuthis reversa Histioteuthidae
Illex illecebrosusOmmastrephidae
Lepidoteuthis grimaldiiLepidoteuthidae
Doryteuthis pealeiiLoliginidae
Loliolus sumatrensisLoliginidae
Lolliguncula brevisLoliginidae
Mastigoteuthis agassiziiMastigoteuthidae
Onykia ingensOnychoteuthidae
Pholidoteuthis massyaePholidoteuthidae
Sepioteuthis lessonianaLoliginidae
Taningia danaeOctopoteuthidae
Taonius borealisCranchiidae
Teuthowenia megalopsCranchiidae
Uroteuthis duvauceliLoliginidae