Editing Squid (section)

===Reproductive system===
[[File:Onykia ingens with erect penis.jpg|thumb|left|Male ''[[Onykia ingens]]'' with penis erected to {{convert|67|cm|in|0|abbr=on}}]]

The sexes are separate in squid, with a single [[gonad]] in the posterior part of the body. Fertilisation is external and usually takes place in the mantle cavity of the female. The male has a [[testis]] from which sperm pass into a single gonoduct where they are rolled together into a long bundle, or spermatophore. The gonoduct is elongated into a "penis" that extends into the mantle cavity and through which spermatophores are ejected. In shallow water species, the penis is short, and the spermatophore is removed from the mantle cavity by a tentacle of the male, which is specially adapted for the purpose and known as a [[hectocotylus]], and placed inside the mantle cavity of the female during mating.<ref name=Ruppert/>

[[File:Uroteuthis duvauceli hectocotylus.jpg|thumb|upright=1.2|[[Hectocotylus]] of ''[[Uroteuthis duvauceli]]'': one tentacle of the male is adapted for transferring the [[spermatophore]].]]

The female has a large translucent [[ovary]], situated towards the posterior of the visceral mass. From here, eggs travel along the gonocoel, where there are a pair of white [[nidamental gland]]s, which lie anterior to the gills. Also present are red-spotted accessory nidamental glands containing [[Symbiosis|symbiotic]] bacteria; both organs are associated with nutrient manufacture and forming shells for the eggs. The gonocoel enters the mantle cavity at the [[gonopore]], and in some species, receptacles for storing spermatophores are located nearby, in the mantle wall.<ref name=Ruppert/>

In shallow-water species of the [[continental shelf]] and [[epipelagic]] or [[mesopelagic zone]]s, it is frequently one or both of arm pair IV of males that are modified into hectocotyli.<ref>{{cite web |url=http://tolweb.org/accessory/Cephalopoda_Glossary?acc_id=587 |title=Hectocotylus |author1=Young, R. E. |author2=Vecchione, M. |author3=Mangold, K. M.|work=Cephalopoda Glossary|publisher=Tree of Life Web Project |access-date=14 December 2018}}</ref> However, most deep-sea squid lack hectocotyl arms and have longer penises; Ancistrocheiridae and Cranchiinae are exceptions.<ref name="Arkhipkin 2010"/> [[Giant squid]] of the genus ''Architeuthis'' are unusual in that they possess both a large penis and modified arm tips, although whether the latter are used for spermatophore transfer is uncertain.<ref name="Arkhipkin 2010"/> Penis elongation has been observed in the deep-water species ''[[Onykia ingens]]''; when erect, the penis may be as long as the mantle, head, and arms combined.<ref name="Arkhipkin 2010" /><ref>{{cite news |last=Walker |first=M. |date=7 July 2010 |url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8792000/8792008.stm |title=Super squid sex organ discovered |work=BBC Earth News}}</ref> As such, deep-water squid have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile [[barnacle]]s.<ref name="Arkhipkin 2010">{{cite journal |last1=Arkhipkin |first1=A. I. |first2=V. V. |last2=Laptikhovsky |year=2010 |title=Observation of penis elongation in ''Onykia ingens'': implications for spermatophore transfer in deep-water squid |journal=Journal of Molluscan Studies |doi=10.1093/mollus/eyq019 |volume=76 |issue=3 |pages=299–300|doi-access=free }}</ref>