Gladius (cephalopod)

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]

Fossilised gladius of Trachyteuthis
Fossilised gladius of Teudopsis
Gladius, showing measurement of rachis and vane

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]

Variability

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

See also

References
  1. Young, R.E.; Vecchione, M.; Mangold, K.M., eds. (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., ed. (2010). "Teudopseina". Tree of Life Web Project.

Further reading
  • 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.) (in Russian and English). Moscow: Institute of Oceanology, SSSR Academy of Sciences. 513 pp.
  • Toll, R.B. (1982). The comparative morphology of the gladius in the order Teuthoidea (Mollusca: Cephalopoda) in relation to systematics and phylogeny (Ph.D.). Coral Gables, Florida: University of Miami. 390 pp.
  • Toll, R.B. (1998). "The gladius in teuthoid systematics". Smithsonian Contributions to Zoology. 586 (1): 55–67.
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