The gladius (plural: ''gladii''), or pen, is a hard internal bodypart found in many
cephalopod
A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s of the superorder
Decapodiformes (particularly
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...
s) and in a single
extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
member of the
Octopodiformes, the
vampire squid (''Vampyroteuthis infernalis'').
It is so named for its superficial resemblance to the
Roman
Roman or Romans most often refers to:
* Rome, the capital city of Italy
* Ancient Rome, Roman civilization from 8th century BC to 5th century AD
*Roman people, the people of ancient Rome
*''Epistle to the Romans'', shortened to ''Romans'', a lett ...
short sword
The English language terminology used in the classification of swords is imprecise and has varied widely over time. There is no historical dictionary for the universal names, classification or terminology of swords; a sword was simply a double ...
of the same name, and is a
vestige
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
of the ancestral
mollusc shell, which was external.
[ The gladius is located ]dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
* Dorsal c ...
ly within the mantle
A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that.
Mantle may refer to:
*Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear
**Mantle (vesture), an Eastern Orthodox ve ...
and usually extends for its entire length. Composed primarily of chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
, it lies within the shell sac, which is responsible for its secretion.
Gladii are known from a number of extinct cephalopod groups, including teudopseids (''e.g.'' '' Actinosepia'', '' Glyphiteuthis'', ''Muensterella
Muensterella is a fossil stem-octopod known from a handful of specimens from German Solnhofen plattenkalk
Plattenkalk is a very finely grained limestone chemically precipitated in a stratified water column under conditions where bioturbation d ...
'', '' Palaeololigo'', '' Teudopsinia'', '' Teudopsis'', and ''Trachyteuthis
''Trachyteuthis'' is a genus of fossil cephalopod, comprising five species: ''T. hastiformis'', ''T. latipinnis'', ''T. nusplingensis'', ''T. teudopsiformis'',
''T. covacevichi''
and ''T. chilensis''.
Taxonomy
The taxonomic placement of ''Trac ...
''), loligosepiids (''e.g.'' '' Geopeltis'', '' Jeletzkyteuthis'', and '' Loligosepia''), and prototeuthids (''e.g.'' ''Dorateuthis
''Dorateuthis'' is a genus of cephalopod with a gladius and soft-part anatomy preserved. Fossils of ''D. syriaca'' are found in Upper Santonian-aged shale of Late Cretaceous Lebanon
Lebanon ( , ar, لُبْنَان, translit=lubnān, ), ...
'', '' Paraplesioteuthis'', and ''Plesioteuthis
''Plesioteuthis'' is an extinct genus of squids, belonging to the family Plesioteuthididae. This genus was first described in 1859, and its fossils were found in the well-known Solnhofen field in Germany.
Species
Species within this genus inclu ...
'').
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.
See also
* Cuttlebone
* Belemnoidea
*Argonaut (animal)
The argonauts ( genus ''Argonauta'', the only extant genus in the family Argonautidae) are a group of pelagic octopuses. They are also called paper nautili, referring to the paper-thin eggcase that females secrete. This structure lacks the gas ...
*Nautilus
The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.
It comprises six living species in ...
* Mollusc shell
References
Further reading
* 513 pp.
* 390 pp.
*
{{Cephalopod anatomy
Cephalopod zootomy
Skeletal system