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Gladius (cephalopod)
Bodypart of certain cephalopods From Wikipedia, the free encyclopedia
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The gladius (pl.: 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] Some species, like the bigfin reef squid, still has a gladius with some degree of mineralization.[3]
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).[4][5]
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![[icon]](#/media/File:Wiki_letter_w_cropped.svg){kind=small} | This section needs expansion with: The terms used to describe the gladius should be elaborated on. You can help by adding to it. (April 2025) |
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;
Fossilized gladii
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Wikimedia Commons has media related to Gladius.
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