Gladius (cephalopod)

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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
AncistroteuthisGladius.jpg Ancistroteuthis lichtensteini Onychoteuthidae
Architeuthis physeteris.jpg Architeuthis sp. Architeuthidae
Bathyteuthis abyssicola gladius.jpg Bathyteuthis abyssicola Bathyteuthidae
Histioteuthis bonnellii gladius.jpg Histioteuthis bonnellii Histioteuthidae
Histioteuthis reversa gladius.jpg Histioteuthis reversa Histioteuthidae
Illex illecebrosus gladius.jpg Illex illecebrosus Ommastrephidae
Lepidoteuthis grimaldii gladius.jpg Lepidoteuthis grimaldii Lepidoteuthidae
Loligo pealeii gladius.jpg Doryteuthis pealeii Loliginidae
Loliolus sumatrensis gladius.jpg Loliolus sumatrensis Loliginidae
Lolliguncula brevis gladius.jpg Lolliguncula brevis Loliginidae
Mastigoteuthis agassizii gladius.jpg Mastigoteuthis agassizii Mastigoteuthidae
Moroteuthis ingens4.jpg Onykia ingens Onychoteuthidae
Pholidoteuthis massyae gladius.jpg Pholidoteuthis massyae Pholidoteuthidae
Sepioteuthis lessoniana gladius.jpg Sepioteuthis lessoniana Loliginidae
Gladius Taningia danae.jpg Taningia danae Octopoteuthidae
Taonius borealis gladius.jpg Taonius borealis Cranchiidae
Teuthowenia megalops gladius.jpg Teuthowenia megalops Cranchiidae
Uroteuthis duvauceli gladius.jpg Uroteuthis duvauceli Loliginidae

See also[edit]


  1. ^ a b c 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 B. 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[edit]

  • (in 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.