All

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, ...

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 have a two-part beak, or

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

, situated in the

buccal mass The digestive system of gastropods has evolved to suit almost every kind of diet and feeding behavior. Gastropods (snails and slugs) as the largest taxonomic class of the mollusca are very diverse: the group includes carnivores, herbivores, scaven ...

and surrounded by the muscular head appendages. The

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 ...

(upper)

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

fits into the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

(lower) mandible and together they function in a scissor-like fashion.Young, R.E., M. Vecchione & K.M. Mangold (1999)
Cephalopoda Glossary

Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site h ...

. The beak may also be referred to as the mandibles or jaws.Tanabe, K., Y. Hikida & Y. Iba (2006). Two coleoid jaws from the Upper Cretaceous of Hokkaido, Japan. ''Journal of Paleontology'' 80(1): 138–145. Fossilised remains of beaks are known from a number of cephalopod groups, both extant and extinct, including

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 fitting t ...

octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...

es,

belemnite Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most ...

s, and vampyromorphs. Aptychi – paired plate-like structures found in

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

s – may also have been jaw elements.

Composition

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 ...

and cross-linked

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s, beaks are more-or-less indigestible and are often the only identifiable cephalopod remains found in the stomachs of predatory species such as

sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus ''Physeter'' and one of three extant species in the sperm whale famil ...

s.Clarke, M.R. (1986). ''A Handbook for the Identification of Cephalopod Beaks''. Oxford University Press, Oxford. Cephalopod beaks gradually become less stiff as one moves from the tip to the base, a gradient that results from differing chemical composition. In hydrated beaks of the

Humboldt squid The Humboldt squid (''Dosidicus gigas''), also known as jumbo squid or jumbo flying squid (EN), and Pota in Peru or Jibia in Chile (ES) is a large, predatory squid living in the eastern Pacific Ocean. It is the only known species of the genus ''D ...

(''Dosidicus gigas'') this stiffness gradient spans two

orders of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...

Measurements

The abbreviations LRL and URL are commonly used in

teuthology Teuthology (from Greek , "cuttlefish, squid", and , ''-logia'') is the study of cephalopods such as octopus, squid, and cuttlefish.

to refer to ''lower rostral length'' and ''upper rostral length'', respectively. These are the standard measures of beak size in

Decapodiformes Decapodiformes is a superorder of Cephalopoda comprising all cephalopod species with ten limbs, specifically eight short arms and two long tentacles. It is hypothesized that the ancestral coleoid had five identical pairs of limbs, and that one ...

; ''hood length'' is preferred for

Octopodiformes Octopodiformes is a superorder of the subclass Coleoidea, comprising the octopuses and the vampire squid. All living members of Octopodiformes have eight arms, either lacking the two tentacles of squid (as is the case in octopuses) or modifying t ...

. They can be used to estimate the mantle length and total body weight of the original animal as well as the total ingested

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

of the species.Gröger, J., U. Piatkowski & H. Heinemann (2000). ''Polar Biology'' 23(1): 70–74.

References

* Aldridge, A.E. (2009). Can beak shape help to research the life history of squid? ''New Zealand Journal of Marine and Freshwater Research'' 43(5): 1061–1067. * Bolstad, K.S. (2006). Sexual dimorphism in the beaks of ''Moroteuthis ingens'' Smith, 1881 (Cephalopoda: Oegopsida: Onychoteuthidae). ''New Zealand Journal of Zoology'' 33(4): 317–327. * Chen, X., H. Lu, B. Liu, Y. Chen, S. Li & M. Jin (2012). Species identification of ''Ommastrephes bartramii'', ''Dosidicus gigas'', ''Sthenoteuthis oualaniensis'' and ''Illex argentinus'' (Ommastrephidae) using beak morphological variables. ''Scientia Marina'' 76(3): 473–481. * Cherel, Y. & K.A. Hobson (2005). Stable isotopes, beaks and predators: a new tool to study the trophic ecology of cephalopods, including giant and colossal squids. ''Proceedings of the Royal Society B: Biological Sciences'' 272(1572): 1601–1607. * Clarke, M.R. & N. MacLeod (1974). Cephalopod remains from a sperm whale caught off Vigo, Spain. ''Journal of the Marine Biological Association of the United Kingdom'' 54(4): 959–968. * Clarke, M.R. & L. Maddock (1988). Beaks of living coleoid Cephalopoda. In: M.R. Clarke & E.R. Trueman (eds.) ''The Mollusca. Volume 12. Paleontology and Neontology of Cephalopods''. Academic Press, San Diego. pp. 121–131. * Clarke, M.R. & R.E. Young (1998). Description and analysis of cephalopod beaks from stomachs of six species of odontocete cetaceans stranded on Hawaiian shores. ''Journal of the Marine Biological Association of the United Kingdom'' 78(2): 623–641. * Hernańdez-García, V., U. Piatkowski & M.R. Clarke (1998). Development of the darkening of ''Todarodes sagittatus'' beaks and its relation to growth and reproduction. ''South African Journal of Marine Science'' 20(1): 363–373. * Hernández-López, J.L. & J.J. Castro-Hernández (2001). ''Fishery Bulletin'' 99(4): 679–684. * Hobson, K.A. & Y. Cherel (2006). Isotopic reconstruction of marine food webs using cephalopod beaks: new insight from captively raised ''Sepia officinalis''. ''Canadian Journal of Zoology'' 84(5): 766–770. * Hsu, C.-C. (2002)
Geomorphometric study of ''Octopus'' and ''Cistopus'' (Cephalopoda: Octopodidae) based on landmarks of beaks
Master's thesis, National Sun Yat-sen University, Kaohsiung, Taiwan. * Ivanovic, M.L. & N.E. Brunetti (1997)
Description of ''Illex argentinus'' beaks and rostral length relationships with size and weight of squids
''Revista de Investigación y Desarrollo Pesquero'' 11: 135–144. * Lalas, C. (2009). Estimates of size for the large octopus ''Macroctopus maorum'' from measures of beaks in prey remains. ''New Zealand Journal of Marine and Freshwater Research'' 43(2): 635–642. * Lefkaditou E. & P. Bekas (2004)
Analysis of beak morphometry of the horned octopus ''Eledone cirrhosa'' (Cephalopoda: Octopoda) in the Thracian Sea (NE Mediterranean)
''Mediterranean Marine Science'' 5(1): 143–149. * Lu, C.C. & R. Ickeringill (2002). ''Museum Victoria Science Reports'' 6: 1–65. * Martínez, P., A. Sanjuan & Á. Guerra (2002). Identification of ''Illex coindetii'', ''I. illecebrosus'' and ''I. argentinus'' (Cephalopoda: Ommastrephidae) throughout the Atlantic Ocean; by body and beak characters. ''Marine Biology'' 141(1): 131–143. * Ogden, R.S., A.L. Allcock, P.C. Watts & J.P. Thorpe (1998). The role of beak shape in octopodid taxonomy. ''South African Journal of Marine Science'' 20(1): 29–36. * Roeleveld, M.A.C. (2000). Giant squid beaks: implications for systematics. ''Journal of the Marine Biological Association of the UK'' 80(1): 185–187. * Uchikawa, K., M. Sakai, T. Wakabayashi & T. Ichii (2009). The relationship between paralarval feeding and morphological changes in the proboscis and beaks of the neon flying squid ''Ommastrephes bartramii''. ''Fisheries Science'' 75(2): 317–323. * Xavier, J.C., M.R. Clarke, M.C. Magalhães, G. Stowasser, C. Blanco & Y. Cherel (2007). ''Arquipélago: Life and Marine Sciences'' 24: 41–48. * Xavier, J.C. & Y. Cherel (2009). British Antarctic Survey, Cambridge. 129 pp. * Xavier, J.C., R.A. Phillips & Y. Cherel (2011). Cephalopods in marine predator diet assessments: why identifying upper and lower beaks is important. ''ICES Journal of Marine Science'' 68(9): 1857–1864. Cephalopod zootomy {{Cephalopod anatomy

Composition

Measurements

References

Further reading