Gladius (cephalopod)

File:Squid gladius, showing measurement of rachis and vane.jpg

The gladius ({{plural form}}: 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).{{cite web |editor1=Young, R.E. |editor2=Vecchione, M. |editor3=Mangold, K.M. |year=1999 |url=http://tolweb.org/accessory/Cephalopod_Gladius_Terminology?acc_id=1955 |title=Cephalopod gladius terminology |website=Tree of Life Web Project}} 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.{{cite journal |last1=Hunt |first1=S. |last2=Nixon |first2=M. |year=1981 |title=A comparative study of protein composition in the chitin-protein complexes of the beak, pen, sucker disc, radula and oesophageal cuticle of cephalopods |journal=Comparative Biochemistry and Physiology B |volume=68 |issue=4 |pages=535–546 |doi=10.1016/0305-0491(81)90071-7}} Some species, like the bigfin reef squid, still has a gladius with some degree of mineralization.{{Cite journal |last1=Messerli |first1=Mark A. |last2=Raihan |first2=M. Jahir |last3=Kobylkevich |first3=Brian M. |last4=Benson |first4=Austin C. |last5=Bruening |first5=Kristi S. |last6=Shribak |first6=Michael |last7=Rosenthal |first7=Joshua J. C. |last8=Sohn |first8=Joel J. |date=2019 |title=Construction and Composition of the Squid Pen from Doryteuthis pealeii |journal=The Biological Bulletin |volume=237 |issue=1 |pages=1–15 |doi=10.1086/704209 |pmc=7340512 |pmid=31441702}}

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).{{cite journal |last1=Fuchs |first1=D. |last2=Engeser |first2=T. |last3=Keupp |first3=H. |year=2007 |title=Gladius shape variation in coleoid cephalopod Trachyteuthis from the Upper Jurassic Nusplingen and Solnhofen Plattenkalks |url=http://www.app.pan.pl/archive/published/app52/app52-575.pdf |journal=Acta Palaeontologica Polonica |volume=52 |issue=3 |pages=575–589}}{{cite web |editor=Fuchs, D. |year=2010 |url=http://tolweb.org/Teudopseina/140241 |title=Teudopseina |website=Tree of Life Web Project}}

Morphology

{{Expand section|The terms used to describe the gladius should be elaborated on|date=April 2025}}

File:Chiroteuthis veranyi immature.jpg

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.]]

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;

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!width=33% | Shape of gladius

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Gladius (cephalopod)

Morphology

See also

References

Further reading