Gladius (cephalopod)

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File:Squid gladius, showing measurement of rachis and vane.jpg
Gladius, showing measurement of rachis and vane
Paralarval chiroteuthids (such as the Chiroteuthis veranyi pictured) are unusual in that they possess a greatly elongated gladius extending well beyond the fins; this supports a long, trailing tail-like structure.
Fossilised gladius of Teudopsis
Fossilised gladius of Trachyteuthis

The gladius (plural: gladii), or pen, is a hard internal bodypart found in many cephalopods of the superorder Decapodiformes (particularly squids) and in a single extant member of the Octopodiformes, the vampire squid (Vampyroteuthis infernalis).[1] 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.[1] 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.[1][2]

Gladii are known from a number of extinct cephalopod groups, including teudopseids (e.g. Actinosepia, Glyphiteuthis, Muensterella, Palaeololigo, Teudopsinia, Teudopsis, and Trachyteuthis), loligosepiids (e.g. Geopeltis, Jeletzkyteuthis, and Loligosepia), and prototeuthids (e.g. Dorateuthis, Paraplesioteuthis, and Plesioteuthis).[3][4]


Gladii are shaped in many distinctive ways and vary considerably between species, though are often like a feather or leaf. Some examples are shown below.

Shape of gladius Species Family
350px Ancistroteuthis lichtensteini Onychoteuthidae
350px Architeuthis sp. Architeuthidae
350px Bathyteuthis abyssicola Bathyteuthidae
350px Histioteuthis bonnellii Histioteuthidae
350px Histioteuthis reversa Histioteuthidae
350px Illex illecebrosus Ommastrephidae
350px Lepidoteuthis grimaldii Lepidoteuthidae
350px Loligo pealeii Loliginidae
350px Loliolus sumatrensis Loliginidae
350px Lolliguncula brevis Loliginidae
350px Mastigoteuthis agassizii Mastigoteuthidae
350px Onykia ingens Onychoteuthidae
350px Pholidoteuthis massyae Pholidoteuthidae
Sepioteuthis lessoniana gladius.jpg Sepioteuthis lessoniana Loliginidae
350px Taningia danae Octopoteuthidae
350px Taonius borealis Cranchiidae
350px Teuthowenia megalops Cranchiidae
350px Uroteuthis duvauceli Loliginidae

See also


  1. 1.0 1.1 1.2 Young, R.E., M. Vecchione & K.M. Mangold (1999). Cephalopod Gladius Terminology. Tree of Life Web Project.
  2. Hunt, S.; Nixon, M. (1981). "A comparative study of protein composition in the chitin-protein complexes of the beak, pen, sucker disc, radula and oesophageal cuticle of cephalopods". Comparative Biochemistry and Physiology Part B: Comparative Biochemistry. 68 (4): 535–546. doi:10.1016/0305-0491(81)90071-7. 
  3. Fuchs, D.; Engeser, T.; Keupp, H. (2007). "Gladius shape variation in coleoid cephalopod Trachyteuthis from the Upper Jurassic Nusplingen and Solnhofen Plattenkalks" (PDF). Acta Palaeontologica Polonica. 52 (3): 575–589. 
  4. Fuchs, D. (2010). Teudopseina. Tree of Life Web Project.

Further reading

  • (Russian) Bizikov, V.A. (1991). Squid gladius: its use for the study of growth, age, intraspecies structure and evolution (on the example of the family Ommastrephidae). Ph.D. Thesis. Institute of Oceanology, SSSR Academy of Sciences, Moscow. 513 pp. (English abstract)
  • Toll, R.B. (1982). The comparative morphology of the gladius in the order Teuthoidea (Mollusca: Cephalopoda) in relation to systematics and phylogeny. Ph.D. Thesis. University of Miami, Coral Gables, Florida. 390 pp.
  • Toll, R.B. (1998). The gladius in teuthoid systematics. Smithsonian Contributions to Zoology 586(1): 55–67.