{{Short description|Species of cephalopod}} {{Speciesbox | image = Octopus minor by OpenCage.jpg | taxon = Octopus minor | authority = (Sasaki, 1920) | synonyms = {{Species list |Polypus macropus minor |Sasaki, 1920 (basionym) |Octopus minor minor |(Sasaki, 1920) |Polypus variabilis |Sasaki, 1929 |Polypus variabilis var. pardalis |Sasaki, 1929 |Polypus variabilis var. typicus |Sasaki, 1929 }} |synonyms_ref = <ref name=WoRMS>{{Cite WoRMS|title=Octopus minor (Sasaki, 1920)|id=342002|access-date=2025-07-24|db=Marine Mollusca}}</ref> }} '''''Octopus minor''''', commonly known as the '''long arm octopus''' or the '''Korean common octopus''', is a small-bodied octopus species distributed along the benthic coastal waters bordering China, Japan, and the Korean Peninsula. It lives at depths ranging from the sea surface to {{convert|200|m|ft fathom|round=50|abbr=off}}.<ref>{{cite web|title=Coastal Mollusks of the Yellow Sea Ecoregion and their habitats|url=https://www.wwf.or.jp/activities/data/200710y-seamap05e.pdf|last=Lifeng|first=Li|date=March 2006|website=Coastal Mollusks of the Yellow Sea Ecoregion and their habitats|access-date=23 April 2020}}</ref><ref>{{Cite journal|date=January 1975|title=Editorial board|journal=Marine Behaviour and Physiology|volume=3|issue=3|pages=ebi|doi=10.1080/10236247509378505|issn=0091-181X}}</ref> ''O. minor'' is commonly found in the mudflats of sub-tidal zones where it is exposed to significant environmental variation.<ref name=":0">{{Cite journal|last1=Kim|first1=Bo-Mi|last2=Kang|first2=Seunghyun|last3=Ahn|first3=Do-Hwan|last4=Jung|first4=Seung-Hyun|last5=Rhee|first5=Hwanseok|last6=Yoo|first6=Jong Su|last7=Lee|first7=Jong-Eun|last8=Lee|first8=SeungJae|last9=Han|first9=Yong-Hee|last10=Ryu|first10=Kyoung-Bin|last11=Cho|first11=Sung-Jin|date=2018-09-25|title=The genome of common long-arm octopus Octopus minor|journal=GigaScience|volume=7|issue=11|article-number=giy119 |doi=10.1093/gigascience/giy119|pmid=30256935|pmc=6279123|issn=2047-217X|doi-access=free}}</ref> It is grouped within the class Cephalopoda along with squids and cuttlefish.<ref name=":1">{{Cite web|last=Vendetti|first=J|date=2006|title=The Cephalopoda|url=https://ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php}}</ref>
''O. minor'' carries cultural and economic value in the countries in which it is found. It is important commercially to the fishing communities in Korea, where it is known as '''''nakji''''', and contributes to the $35 million octopus industry.<ref>{{cite web|title=South Korean fisherman, Health officials tangle over Octopus|url=https://www.latimes.com/archives/la-xpm-2010-oct-29-la-fg-korea-octopus-20101029-story.html|last=Glionna|first=J|date=2010|website=Los Angeles Times|access-date=24 April 2020}}</ref> It is a Korean seafood, commonly referred to as ''nakji'' ({{Korean|hangul=낙지}}). The octopus is served both cooked and raw, and is often a snack during sporting events.<ref name=":2">{{cite web|title=Nakji bokkeum, the classic Korean octopus dish that's a stated specialty of|url=https://www.seattleweekly.com/food/nakji-bokkeum-the-classic-korean-octopus-dish-thats-a-stated-specialty-of/|last=Raskin|first=Hanna|date=2013-01-22|website=Seattle Weekly|language=en-US|access-date=2020-05-26}}</ref>
There have been multiple findings concerning the physiological makeup of ''O. minor''. It has been shown to host a dangerous parasite, while also demonstrating the ability to adapt its morphology to a wide range of environmental conditions. These characteristics have increased interest in the species and its genome has been mapped.<ref name=":0" /><ref name=":3">{{Cite journal|last1=Du|first1=Xin|last2=Dong|first2=Chao|last3=Sun|first3=Shi-Chun|date=2018-10-01|title=Octopicola huanghaiensis n. sp. (Copepoda: Cyclopoida: Octopicolidae), a new parasitic copepod of the octopuses Amphioctopus fangsiao (d'Orbigny) and Octopus minor (Sasaki) (Octopoda: Octopodidae) in the Yellow Sea|journal=Systematic Parasitology|volume=95|issue=8–9|pages=905–912|doi=10.1007/s11230-018-9819-8|pmid=30276653|s2cid=52896143|issn=0165-5752}}</ref>
== Taxonomic status == This species was published as one subgroup of the species, ''Polypus macropus'' var. ''minor'' <small>Sasaki, 1920</small> by Madoka Sasaki, Japanese Malacologist.<ref>{{Cite journal|last=Sasaki|first=M.|author-link=Madoka Sasaki |date=1920 |title=Report on cephalopods collected during 1906 by the United States Bureau of Fisheries steamer Albatross in the northwestern Pacific|journal=Proceedings of the U.S. National Museum |volume=57 |issue=2310|pages=163–203|doi=10.5479/si.00963801.57-2310.163|issn=0096-3801|url=https://www.biodiversitylibrary.org/part/38411 }}</ref><ref>He used the term "var.", but it was before 1961, and do not intend to place the rank lower than subspecies, so the name ''minor'' is available as a subspecific name under Article 45.6.4. in ICZN. He also used genus ''Polypus'' <small>Schneider, 1784</small> according to following Hoyle's work in 1901, despite ''Polypus'' <small>Schneider, 1784</small> is non-binomial. Today, ''Polypus'' <small>Hoyle, 1901</small> is treated as ''Octopus'' <small>Cuvier, 1979</small> because of its priority.</ref> Later, he moved it to another species, ''Polypus variabilis'' <small>Sasaki, 1929</small> var. ''minor'' <small>Sasaki, 1920</small>, to distinguish it from ''P. macropus'' (=''Callistoctopus macropus'').<ref>{{Cite journal|last=Sasaki|first=M.|author-link=Madoka Sasaki |date=1929|title=A Monograph of the Dibranchiate Cephalopods of the Japanese and Adjacent Water|issue=suppl |pages=95–96|place=Sapporo|journal=Journal of the Faculty of Agriculture, Hokkaido Imperial University|volume=20 |hdl=2115/12617 |url=https://hdl.handle.net/2115/12617}}</ref> In 1965, Iwao Taki transferred the name to ''Octopus minor'' <small>(Sasaki, 1920)</small>.<ref>{{Cite book|last=Taki|first=I.|author-link=Iwao Taki |date=1965 |chapter=Cephalopoda|editor1=Y. K. Okada|editor2=S. Uchida|editor3=T. Uchida|title=New Illustrated Encyclopedia of the Fauna of Japan, vol. 2|pages=307–326|publisher=Hokuryukan |place=Tokyo|lang=ja}}</ref> Sometimes referred as '''Octopus' minor'', because genus ''Octopus'' is paraphyletic.<ref name="Norman_et_al_2016">{{Cite book|last1=Norman |first1=M.D. |last2=Finn |first2=J. K. |last3=Hochberg |first3=F.G. |date=2016|chapter=Family Octopodidae |pages=200–201|editor=Jereb, P.; Roper, C.F.E.; Norman, M.D.; Finn, J.K.|title=Cephalopods of the world. An annotated and illustrated catalogue of cephalopod species known to date. Volume 3. Octopods and Vampire Squids|series=FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 3 |place=Rome|publisher=Food and Agriculture Organization of the United Nations |isbn=978-92-5-107989-8}}</ref>
Kaneko ''et al.'' (2011) noted that ''O. minor'' is the member of genus ''Callistoctopus'' <small>Taki, 1964</small> morphologically and phylogenetically based on mtDNA (''COI'' and ''COIII''); they subsequently renamed it into '''''Callistoctopus minor''''' <small>(Sasaki, 1920)</small>.<ref>{{Cite journal|last1=Kaneko|first1=N. |last2=Kubodera|first2=T. |author2-link=Tsunemi Kubodera |last3=Iguchi|first3=A.|date=2011|title=Taxonomic Study of Shallow-Water Octopuses (Cephalopoda: Octopodidae) in Japan and Adjacent Waters using Mitochondrial Genes with Perspectives on Octopus DNA Barcoding |journal=Malacologia |volume=54|issue=1–2|pages=97–108|doi=10.4002/040.054.0102|url=https://www.biodiversitylibrary.org/part/388784 }}</ref> This relationship is supported by subsequent research teams in their own phylogenetic analyses.<ref>{{Cite journal|last1=Acosta-Jofré |first1=M.S. |last2=Sahade |first2=R. |last3=Laudien|first3=J. |last4=Chiappero|first4=M.B. |date=2012|title=A contribution to the understanding of phylogenetic relationships among species of the genus ''Octopus'' (Octopodidae: Cephalopoda) |journal=Scientia Marina |volume=76|issue=2|pages=311–318|doi=10.3989/scimar.03365.03B|bibcode=2012ScMar..76..311A }}</ref><ref>{{Cite journal|last1=de Luna Sales |first1=J.B. |last2=Haimovici |first2=M. |last3=Ready |first3=J.S. |last4=Souza |first4=R.F. |last5=Ferreira |first5=Y. |last6=de Cassia Silva Pinon |first6=J. |last7=Costa |first7=L.F.C. |last8=Asp |first8=N.E. |last9=Sampaio |first9=I. |last10=Schneider |first10=H. |date=2019 |title=Surveying cephalopod diversity of the Amazon reef system using samples from red snapper stomachs and description of a new genus and species of octopus |journal=Sci. Rep. |volume=9|number=5956|page=5956 |doi=10.1038/s41598-019-42464-8|pmid=30976082|pmc=6459862|bibcode=2019NatSR...9.5956D }}</ref><ref>{{Cite journal|last1=Ibáñez|first1=C.M. |last2=Fenwick|first2=M. |last3=Ritchie|first3=P. A. |last4=Carrasco|first4=S. A. |last5=Pardo-Gandarillas|first5=M. C.|date=2020|title=Systematics and Phylogenetic Relationships of New Zealand Benthic Octopuses (Cephalopoda: Octopodoidea) |journal=Front. Mar. Sci. |volume=7|issue=182|pages=1–13|article-number=182 |doi=10.3389/fmars.2020.00182|doi-access=free |bibcode=2020FrMaS...7..182I }}</ref><ref>{{Cite journal|last1=Magallón-Gayón|first1=E. |last2=del Río-Portilla|first2=M.Á. |last3=Barriga-Sosa|first3=I. de los A.|date=2020 |title=The complete mitochondrial genomes of two octopods of the eastern Pacific Ocean: ''Octopus mimus'' and'' 'Octopus' fitchi'' (Cephalopoda: Octopodidae) and their phylogenetic position within Octopoda|journal=Molecular Biology Reports |volume=47|issue=2 |pages=943–952|doi=10.1007/s11033-019-05186-8|pmid=31758495 }}</ref><ref name="Tenuipes">{{cite journal |last1=Li |first1=Jiahua |last2=Xu |first2=Chenxi |last3=Zheng |first3=Xiaodong |title=Morphological Description and Phylogenetic Analyses of a New Species of Callistoctopus (Cephalopoda, Octopodidae) from China |journal=Diversity |date=8 December 2022 |volume=14 |issue=12 |page=1083 |doi=10.3390/d14121083 |bibcode=2022Diver..14.1083L |doi-access=free }}</ref><ref name="Taite_et_al_2023">{{Cite journal|last1=Taite|first1=M.|first2=F.Á. |last2=Fernández-Álvarez |first3=H.E. |last3=Braid |first4=S.L. |last4=Bush |first5=K. |last5=Bolstad |first6=J. |last6=Drewery |first7=S. |last7=Mills |author8=Strugnell, J.M.; Vecchione, M.; Villanueva, R.; Voight, J.R. & Allcock, A.L. |date=2023|title=Genome skimming elucidates the evolutionary history of Octopoda |journal=Molecular Phylogenetics and Evolution|volume=182|article-number=107729|doi=10.1016/j.ympev.2023.107729|pmid=36773750 |bibcode=2023MolPE.18207729T |hdl=10261/329953 |hdl-access=free }}</ref> Several researchers still use the old name "''Octopus minor''",<ref name="Taite_et_al_2023"/> as the World Register of Marine Species still considers it a species of ''Octopus''.<ref name=WoRMS/>
== Anatomy == [[File:Long arm octopus (Octopus minor).jpg|thumb|''Nakji'' at a market in South Korea]] ''O. minor'', similar to the rest of its order Octopoda, is bilaterally symmetrical along a dorsoventral axis with two eyes and mouth surrounded by eight webbed arms.<ref name=":4">{{Citation|date=2020|title=Invertebrate Zoology [Working Title]|doi=10.5772/intechopen.82957|s2cid=243042155 }}</ref> These arms contain two-thirds of the octopus's neurons.<ref name=":5">{{Cite book|last=Wells|first=M. J.|date=1978|title=Octopus|doi=10.1007/978-94-017-2468-5|isbn=978-94-017-2470-8}}</ref> On the underside of these arms, ''O. minor'' has "suckers" which are circular, adhesive suction cups. These are predominantly used for manipulation, navigation, and for preparing food.<ref name=":4" /><ref name=":5" /> ''O. minor'' has a bulbous mantle and visceral hump which contains the majority of its fundamental organs.<ref>{{Citation |chapter=Cephalopoda |doi=10.1007/3-540-31078-9_29 |title=Paleontology |series=Encyclopedia of Earth Science |date=1979 |last1=Glenister |first1=Brian F. |pages=170–183 |isbn=0-87933-185-2 }}</ref>
''O. minor'' is small and soft-bodied with long arms, hence its nickname "long-arm octopus",<ref name=":6">{{Citation |last=El-Bawab |first=Fatma |title=Phylum Mollusca |date=2020 |work=Invertebrate Embryology and Reproduction |pages=713–813 |publisher=Elsevier |doi=10.1016/b978-0-12-814114-4.00011-4 |isbn=978-0-12-814114-4 |s2cid=241314970}}</ref> or "whiparm octopus".<ref name="Norman_et_al_2016"/> Japanese common name is also "long-arm octopus" ({{lang|ja|テナガダコ}}, 手長蛸, ''tenaga-dako'').<ref name="Habe_1981">{{Cite journal|last1=Habe|first1=T.|author1-link=:ja:波部忠重|date=1981|title=A Catalogue of Molluscs of Wakayama Prefecture, the Province of Kii I. Bivalvia, Scaphopoda and Cephalopoda|journal=Publications of the Seto Marine Biological Laboratory. Special Publication Series|volume=7 |page=250|lang=ja|doi=10.5134/176470 |url=https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/176470/1/fic007_xiii.pdf}}</ref><ref name="Kubodera_2013">{{Cite book|last1=Kubodera|first1=T. |author1-link=Tsunemi Kubodera|chapter=Chapter 9 Japanese octopus pictorial book |page=226 |title=Octopus biology|date=5 Jun 2013|editor=Takashi Okutani|editor-link=:ja:奥谷喬司|publisher=Tokai University Press|place=Hadano, Kanagawa|isbn=978-4-486-01941-1}}</ref>
Their body surface is mostly smooth, with small pimples scattered on the dorsal surface.<ref name="Kubodera_2013"/> Live ''O. minor'' shows red-brown with light yellow spots on dorsal surfaces.<ref name="Norman_et_al_2016"/> It can be identified by its grey colouring which matches the sandy plains in which it is commonly found, however when it finds itself threatened or in danger, it will shift its coloration to a dark red.<ref name=":1" />
Arms are thin and remarkably unequal in length. The first arm, the longest one, is about 80% of total length,<ref name="Kubodera_2013"/> which is twice length of third or fourth arms.<ref name="Norman_et_al_2016"/>
Funnel organ is VV-shaped.<ref name="Kubodera_2013"/>
Male has a hectocotylized arm to use for the mating. It is formed on right third arm, about half length of the left third arm. Ligula, the tip of the hectocotylized arm is large, spoon-shaped about 10–20% of the arm with about 42–48 suckers.<ref name="Kubodera_2013"/> Mature male also has enlarged suckers around level of 8th or 9th sucker pair, largest on the first arms.<ref name="Norman_et_al_2016"/>
=== Size === The ''O. minor'' reaches a mantle size of {{convert|18|cm|in|frac=2|abbr=off}} with arms of up to {{convert|65|cm|in|frac=2|abbr=on}}.<ref>{{cite web|title=Octopus bimaculoides Care Sheet (two-spot octopus)|url=https://tonmo.com/articles/octopus-bimaculoides-care-sheet-two-spot-octopus.6/|website=The Octopus News Magazine Online|date=8 March 2019 |language=en-US|access-date=2020-05-26}}</ref> It is on the smaller side of its class, compared to colossal squids which can reach lengths of over 10 metres (33 feet).<ref>{{cite web|title=Giant Squid {{!}} Smithsonian Ocean|url=https://ocean.si.edu/ocean-life/invertebrates/giant-squid|website=ocean.si.edu|date=30 April 2018 |language=en|access-date=2020-05-26}}</ref>
== Distribution and behaviour ==
=== Feeding === ''O. minor'', like other octopus populations, possesses predatory traits.<ref name=":7">{{cite journal|title=Digitoxin Metabolism by Rat Liver Microsomes|last1=A|first1=Schmoldt|last2=Hf|first2=Benthe|date=1975-09-01|journal=Biochemical Pharmacology|language=en|pmid=10|last3=G|first3=Haberland|volume=24|issue=17|pages=1639–41|doi=10.1016/0006-2952(75)90094-5|hdl=10033/333424|hdl-access=free}}</ref> ''O. minor's'' diet coincides with that of other bottom-dwelling octopuses, with over 50% of its prey being fish, 25% by shellfish such as whelks and clams, the remainder being made up of crustaceans such as crabs, along with annelids and nematodes, other commonly found species sharing their habitat with ''O. minor''.<ref name=":8">{{Cite journal|last1=Bo|first1=Qi-Kang|last2=Zheng|first2=Xiao-Dong|last3=Chen|first3=Zhi-Wei|date=2020-01-27|editor-last=Chapman|editor-first=Maura (Gee) Geraldine|title=Feeding intensity and molecular prey identification of the common long-armed octopus, Octopus minor (Mollusca: Octopodidae) in the wild|journal=PLOS ONE|language=en|volume=15|issue=1|article-number=e0220482|doi=10.1371/journal.pone.0220482|issn=1932-6203|pmc=6984699|pmid=31986139|bibcode=2020PLoSO..1520482B|doi-access=free}}</ref> The smaller size of the octopus means rejection of larger species including rock scallops and large fish.<ref name=":7" /><ref name=":8" /> thumb|187x187px|Octopus "suckers" The benthic nature of ''O. minor'' allows it to move between rocks and through crevices.<ref name=":8" /> Once it has identified its prey, it makes a sudden pounce, using its suckers to grip on and pull it in.<ref>{{cite journal|title=The Effect of Adrenaline and of Alpha- And Beta-Adrenergic Blocking Agents on ATP Concentration and on Incorporation of 32Pi Into ATP in Rat Fat Cells|last=Jm|first=Stein|date=1975-09-15|journal=Biochemical Pharmacology|volume=24|issue=18|pages=1659–62|doi=10.1016/0006-2952(75)90002-7|language=en|pmid=12}}</ref> The ''O. minor'' preys on smaller animals by trapping them in the web-like structure of its legs.<ref name=":7" /> The ''O. minor'' injects its prey with a paralyzing saliva, using miniature teeth at the end of its salivary papilla to dismember them.<ref name=":7" /> When targeting shelled molluscs, the ''O. minor'' creates a toxic saliva that enables the calcium carbonate of the shell to be broken down.<ref name=":8" /> Once the outer protection is penetrated, the prey's muscles relax, allowing the octopus to remove and eat its prey's soft tissues.<ref name=":7" /><ref name=":8" />
Feeding intensities differ between the males and females of the species.<ref name=":8" /> Different intensities revolve around the ovarian maturation calendar of the female octopus.<ref name=":8" /> From the months of April to July the intensity of feeding in females decreases, while in males it increases.<ref name=":8" /> While 10 different taxa have been identified within the stomach of the ''O. minor'', the family Gobiidae was most prevalent during the female's ovarian maturation.<ref name=":8" /> thumb|''O. minor'' with scale
=== Locomotion === Different to other multi-limbed hydrostats such as crabs, the ''O. minor'' performs movements using all eight independent limbs.<ref name=":9">{{Cite journal|last1=Taylor|first1=Jennifer R. A.|last2=Kier|first2=William M.|date=April 2006|title=A pneumo-hydrostatic skeleton in land crabs|journal=Nature|language=en|volume=440|issue=7087|page=1005|doi=10.1038/4401005a|pmid=16625186|s2cid=4431354|issn=0028-0836|doi-access=free}}</ref> The arrangement of muscles within its arms allows for movement in any direction.<ref name=":10">{{Cite journal|last=Huffard|first=C. L.|date=2006-10-01|title=Locomotion by Abdopus aculeatus (Cephalopoda: Octopodidae): walking the line between primary and secondary defenses|journal=Journal of Experimental Biology|language=en|volume=209|issue=19|pages=3697–3707|doi=10.1242/jeb.02435|pmid=16985187|issn=0022-0949|doi-access=free|bibcode=2006JExpB.209.3697H }}</ref> Movements of the ''O. minor'' involve crawling between rocks and crevices, and swimming with its dorsal fin in a leading position.<ref name=":10" /> Jet propulsion is another form of locomotion also used by the ''O. minor''.<ref name=":10" /> The process of crawling involves the use of the octopus's suckers.<ref name=":11">{{cite journal|title=Action of Propranolol on Mitochondrial Functions--Effects on Energized Ion Fluxes in the Presence of Valinomycin|last1=J|first1=Järvisalo|last2=Ne|first2=Saris|date=1975-09-15|journal=Biochemical Pharmacology|volume=24|issue=18|pages=1701–5|doi=10.1016/0006-2952(75)90009-x|language=en|pmid=13}}</ref> Some are used to grip to surrounding environments allowing the octopus to pull itself forward with its legs. Others push from behind.<ref name=":11" /> This process is repeated until a change of locomotion is performed.<ref name=":11" />
The ''O. minor'' performs a swimming motion using the expulsion of water from the mantle through its siphon into the ocean behind it.<ref name=":10" /><ref name=":12">{{Cite journal|last1=Kassim|first1=I.|last2=Phee|first2=L.|last3=Ng|first3=W.S.|last4=Feng Gong|last5=Dario|first5=P.|last6=Mosse|first6=C.A.|date=May 2006|title=Locomotion techniques for robotic colonoscopy|journal=IEEE Engineering in Medicine and Biology Magazine|volume=25|issue=3|pages=49–56|doi=10.1109/MEMB.2006.1636351|pmid=16764431|bibcode=2006IEMBM..25R..49K |s2cid=9124611|issn=0739-5175}}</ref> Force provided by the water allows the octopus to move in the opposite direction.<ref name=":12" /> The direction of movement is dependent on the way in which the siphon is faced. The long arms found on the ''O. minor'' provide it with a streamline swimming shape. Its bilateral symmetry allows it to move headfirst, with its legs trailing.<ref name=":10" /><ref name=":12" /> Jet swimming is used predominantly to escape from danger.<ref name=":9" />
The ''O. minor'' performs a movement known as "pumping". This involves the legs of the ''O. minor'' contracting in unison, allowing for the production of a wave.<ref name=":10" /> This provides a force which moves the body. The ''O. minor'' uses its appendages to crawl outside of the water.<ref name=":16">{{Cite journal|last1=Wood|first1=James B.|last2=Anderson|first2=Roland C.|date=April 2004|title=Interspecific Evaluation of Octopus Escape Behavior|journal=Journal of Applied Animal Welfare Science|language=en|volume=7|issue=2|pages=95–106|doi=10.1207/s15327604jaws0702_2|pmid=15234886|s2cid=16639444|issn=1088-8705}}</ref> For the ''O. minor'' this is performed between tide pools and when served as a culinary option.<ref name=":16"/>
=== Habitat === The habitats of ''O. minor'' vary greatly between rocks, reefs and the ocean floor.<ref name=":14">{{Cite journal|last1=Kang|first1=J.-H.|last2=Park|first2=J.-Y.|last3=Choi|first3=T.-J.|date=2012|title=Genetic differentiation of octopuses from different habitats near the Korean Peninsula and eastern China based on analysis of the mDNA cytochrome C oxidase 1 gene|journal=Genetics and Molecular Research|volume=11|issue=4|pages=3988–3997|doi=10.4238/2012.november.21.2|doi-broken-date=23 July 2025 |pmid=23212336|issn=1676-5680|doi-access=free}}</ref> It is a benthic octopus, meaning it lies at the lowest body of water, around the sediment surface and rock or coral cover.<ref name=":14" /> ''O. minor'' is located within the mudflats of sub-tidal zones surrounding the south western coast of the Korean peninsula.<ref name=":1" /> ''O. minor'' residing within the mudflats of coastal regions are exposed to high salinity, temperature and water movement conditions.<ref name=":0" /> The ''O. minor'' is found in rocky areas such as Jeju Island.<ref name=":14" />
The ''O. minor'' is commonly found in the Yellow Sea.<ref name=":14" /> This is a segment of the Western Pacific Ocean situated between the Korean Peninsula and mainland China, connected to the Gulf of Bohai.<ref name=":15">{{cite web|title=Yellow Sea|url=https://www.britannica.com/place/Yellow-Sea|last1=Uda|last2=Valencia|date=2020|website=Britannica|access-date=25 May 2020}}</ref> The sea extends over 950 kilometres from North to South and 700 kilometres wide.<ref name=":15" /> The sea has a cyclone current and semidiurnal tides with temperatures that range from -10 degrees Celsius to 28 degrees Celsius.<ref name=":15" />
=== Colour change === The ''O. minor'', when hunting and avoiding predators, use specialised pigment-filled bags known as chromatophores. These are found in the skin, allowing the octopus to adjust its color or reflectivity.<ref name=":16"/> Colour variation of chromatophores include red, brown, black, grey, yellow or blue.<ref name=":1" /> Other colour methods include the use of an iridescent dermal tissue.<ref name=":16" /> This manipulated by the ''O. minor'' to communicate with other octopus and proceed with courtship rituals.<ref name=":1" />
The ''O. minor'' possesses muscles on its mantle which change texture to assist in changing colour.<ref name=":1" /> The shallow water habitats which the ''O. minor'' inhabits has allowed it to evolve more diverse skin than fellow cephalopods.<ref name=":1" />
=== Renal parasites === thumb|100px|''Dicyema clavatum'' The ''O. minor'' has three species of dicyemids in their renal sac: ''Dicyema clavatum'', ''Dicyema sphyrocephalum'', ''Dicyema dolichocephalum''.<ref>{{Cite journal|last1=Furuya |first1=H. |author1-link=:ja:古屋秀隆 |last2=Tsuneki |first2=K. |last3=Koshida |first3=Y.|date=1992|title=Two New Species of the Genus ''Dicyema'' (Mesozoa) from Octopuses of Japan with Notes on ''D. misakiense'' and ''D. acuticephalum''|journal=Zoological Science |volume=9|issue=2|pages=423–437|doi=10.34425/zs000974}}</ref><ref>{{Cite journal|last1=Furuya |first1=H. |author1-link=:ja:古屋秀隆 |date=2020 |title=Current taxonomic studies on dicyemid fauna in the Kumano Sea |journal=TAXA |volume=48 |pages=3–12|doi=10.19004/taxa.48.0_3|lang=ja}}</ref>
== Relationship to humans == [[File:Octopuses in Cheju Island Fish Market.jpg|thumb|Sold on Jeju Island, South Korea]] ''O. minor'' is well represented within the Korean commercial fishery field, presenting a high annual yield of over 350,000 tonnes.<ref name=":0" /><ref>{{cite web|title=Octopus as Food - Octopus Facts and Information|date=6 March 2014 |url=https://octopusworlds.com/octopus-as-food/|language=en-US|access-date=2020-05-26}}</ref> This has led to its inclusion within multiple signature seafood dishes, mostly found in Korea.<ref name=":17">{{Cite journal|last=Jasti|first=Sunitha|date=2011|title=Gender, Acculturation, Food Patterns, and Overweight in Korean Immigrants|journal=American Journal of Health Behavior|volume=35|issue=6|pages=734–45|doi=10.5993/ajhb.35.6.9|pmid=22251764|issn=1087-3244}}</ref> The rapid adaption of the octopus to the stressful conditions of its habitat encouraged scientific research and the mapping of its genome.<ref>{{Cite journal|last1=Muhammad|first1=Faiz|last2=Dou|first2=Canfeng|last3=Lü|first3=Zhen-ming|last4=Gong|first4=Li|last5=Du|first5=Xun|last6=Shafi|first6=Muhammad|date=2018|title=Genetic Structure of Octopus minor (Sasaki, 1920) (Cephalopoda: Octopoda) from Chinese Waters using Mitochondrial ATPase 6 Gene|journal=Pakistan Journal of Zoology|volume=51|issue=1|doi=10.17582/journal.pjz/2019.51.1.sc5|issn=0030-9923|doi-access=free}}</ref><ref name=":0" />
=== Culinary use === Within most parts of Korea, ''O. minor'' or ''Nakji,'' is a culinary option, being served most commonly as a snack either raw, cooked or poached.<ref name=":17" />
==== Nakji-bokkeum (cooked) ==== For this dish, ''O. minor'' is chopped, then stir-fried with vegetables such as carrots, onions and cabbage.<ref name=":18">{{cite web|title=Korean recipes: spicy stir-fried small octopus, nakji bokkeum (낙지볶음)|url=http://www.korea.net/NewsFocus/Culture/view?articleId=132155|website=Korea.net|access-date=2020-05-26}}</ref> It is marinated with a local Korean red pepper sauce, then served hot with warm rice, somyeon, or bean sprouts.<ref name=":18" /><ref name=":2" />
==== San-nakji (raw) ==== For this dish'', O. minor'' is either chopped or whole and served raw on a plate. It is often served with sesame oil and sesame seeds.<ref name=":19">{{cite web|title=San-nakji live raw octopus|url=http://www.eatinkorea.com/en/food/sannakji-live-raw-octopus|website=www.eatinkorea.com|access-date=2020-05-26}}</ref> The significant number of nerve endings in the arms of the ''O. Minor'' combined with its sophisticated nervous system, allows for a variety of movements when disconnected from the brain, meaning the octopus performs movements whilst being served.<ref name=":19" /><ref>{{cite web|title=Octopus Facts|url=https://www.livescience.com/55478-octopus-facts.html|first=Alina |last=Bradford |website=livescience.com|date=8 June 2017|language=en|access-date=2020-05-26}}</ref> As the suction cups are still active on the cephalopod's arms, they may grip to one's throat, therefore consumers are at risk of choking.<ref name=":19" />
==== Nakji-yeonpo-tang (soup) ==== For this dish, ''O. minor'' is boiled in stock, before being chopped into fine pieces then served in the soup with spring onion, chilli and minced garlic. The dish is traditionally offered during funeral processions.<ref>{{cite web|title=Nakji Jeongol (Korean Octopus Stew)|url=https://thedomesticman.com/2016/07/05/nakji-jeongol-korean-octopus-stew/|date=2016-07-05|website=The Domestic Man|language=en|access-date=2020-05-26}}</ref>
<gallery mode="packed" widths="150px" heights="150px"> File:Nakji-bokkeum.jpg|Nakji-bokkeum (cooked) File:San-nakji (32013691345).jpg|San-nakji (raw) File:Korean soup-Galbi-nakji-yeonpo-tang.jpg|Nakji-Yeonpo-tang (soup) File:Nakji-jeongol 5.jpg|Nakiji-jeongol </gallery>
=== Dangers === A large percentage (22%) of ''O. minor'' have been found to host a dangerous parasitic benthic crustacean.<ref name=":3" /> Their increased susceptibility is due to its lack of external shell compared to other molluscs, such as snails.<ref>{{Cite journal|last1=Roumbedakis|first1=Katina|last2=Drábková|first2=Marie|last3=Tyml|first3=Tomáš|last4=di Cristo|first4=Carlo|date=2018-11-20|title=A Perspective Around Cephalopods and Their Parasites, and Suggestions on How to Increase Knowledge in the Field|journal=Frontiers in Physiology|volume=9|article-number=1573|doi=10.3389/fphys.2018.01573|pmid=30515100|pmc=6255944|issn=1664-042X|doi-access=free}}</ref> The presence ''Octopicola huanghaienis'' parasite is identified by a spike at the end of its labrum lap.<ref name=":3" /> The parasite is a health concern when ''O. minor'' is served raw.<ref name=":3" />
== Genetic research == ''O. minor's'' adaption of its behavioral repertoire to assorted habitat conditions made it a promising model to be studied and to have its genome mapped.<ref name=":0" /> Distributions of the ''O. minor'' between the Korean Peninsula and Eastern China identified genetic differences in individuals from different habitats.<ref name=":14" /> The borders of these countries are connected by the Yellow Sea. Genetic structures of ''O. minor'' were analysed using a sequence of the ''CO1'' gene as it shows higher base-substitution mutation rates.<ref name=":14" />
=== Genome mapping === The morphology of the ''O. minor'' was analysed for genome mapping.<ref name=":0" /> ''O. minor'' was studied for its ability to tolerate environmental changes. Its molecular basis was studied for plasticity development and mechanisms underlying adaption.<ref name=":0" /> The concluding genome assembly of the octopus was 5.09 Gb, with over 30 010 genes; 44% were made up of repeated elements.<ref name=":0" /><ref name=":14" /> The total number of gene families within ''O. Minor'' are 178.<ref name=":14" /> A highly identical nucleotide sequence across multiple species suggests the ''O. minor'' is close to ''Callistoctopus ornatus'' and ''Callistoctopus luteus''. ''Octopus minor'' has various Korean names, but it is actually the same species as despite them occupying different habitats.<ref name=":14" />
== References == {{Reflist|30em}}
{{Taxonbar|from=Q76565}}
Category:Cephalopods described in 1920 Category:Cephalopods of Asia Category:Molluscs of the Pacific Ocean Category:Octopodidae Category:Korean seafood