Editing Octopus (section)

===Reproduction===
[[File:Tremoctopus violaceus5.jpg|thumb|upright|Adult male ''[[Tremoctopus violaceus]]'' with [[hectocotylus]]|alt=Drawing of a male octopus with one large arm ending in the sexual apparatus]]

Octopuses [[Gonochorism|have two sexes]] and have only one gonad ([[testis]] in males and [[ovary]] in females) located posteriorly. The gonad deposits [[gamete]]s into an adjacent cavity called the gonocoel. A [[gonoduct]] bridges the gonocoel with the [[mantle cavity]].<ref name=Ruppert/>{{rp|363–365}} An [[optic gland]] creates hormones that cause the octopus to mature and age and stimulate gamete production. The timing of reproduction and lifespan depends on environmental conditions such as temperature, light and nutrition, which trigger the gland.<ref name=Mather/>{{rp|147}}<ref>{{cite journal |last1=Wells |first1=Martin J. |last2=Wells |first2=J. |year=1972 |title=Optic glands and the state of the testis in ''Octopus'' |journal=Marine Behaviour and Physiology |volume=1 |issue=1–4 |pages=71–83 |doi=10.1080/10236247209386890}}</ref> The male has a specialised arm called a [[hectocotylus]] which it uses to transfer [[spermatophore]]s (packets of sperm) into the female's mantle cavity.<ref name=Ruppert/>{{rp|363–365}} The hectocotylus in ''Octopus'' is usually the R3 arm, which has a spoon-shaped depression and a suckerless tip.<ref name=Wells/>{{rp|12–14}}<ref name=Ruppert/>{{rp|363–365}} Fertilisation may occur in the mantle cavity or in the surrounding water.<ref name=Ruppert/>{{rp|363–365}}

Reproduction has been studied in some species. In the [[giant Pacific octopus]], courtship includes changes in skin texture and colour, mostly in the male. The male may cling to the top or side of the female or position himself beside her. There is some speculation that he may first use his hectocotylus to remove any spermatophore or sperm already present in the female. He picks up a spermatophore from his spermatophoric sac with the hectocotylus, inserts it into the female's mantle cavity, and deposits it in the correct location in the opening of the oviduct. Two spermatophores are transferred in this way; these are about one metre (yard) long, and the empty ends may protrude from the female's mantle.<ref name=Crowfootreproduction>{{cite web |url=http://www.asnailsodyssey.com/LEARNABOUT/OCTOPUS/octoRepr.php |title=Octopuses and Relatives: Reproduction |last=Carefoot |first=Thomas |work=A Snail's Odyssey |access-date=11 April 2017 |archive-url=https://web.archive.org/web/20170422215052/http://www.asnailsodyssey.com/LEARNABOUT/OCTOPUS/octoRepr.php |archive-date=22 April 2017 |url-status=dead }}</ref> A complex hydraulic mechanism releases the sperm from the spermatophore.<ref name=Ruppert/>{{rp|363–365}} 

[[File:Enteroctopus dofleini to spawn.jpg|thumb|left|Female giant Pacific octopus guarding strings of eggs|alt=A female octopus underneath hanging strings of her eggs]]

The eggs have large yolks; [[cleavage (embryo)|cleavage]] (division) is relatively shallow and a [[germinal disc]] develops at the pole. During [[gastrulation]], the disc surrounds the yolk, forming a yolk sac, which eventually forms part of the gut. The embryo forms as the dorsal side of the disc grows upward, with a shell gland, gills, mantle and eyes on its dorsal side. The arms and funnel form on the ventral side of the disc, with the former moving upward to surround the mouth. The embryo consumes the yolk during development.<ref name=Ruppert/>{{rp|363–365}} 

Over a month after mating, Giant Pacific octopuses lay eggs. The species can lay 180,000 eggs in a single clutch, while ''[[Octopus rubescens|O. rubescens]]'' clutches host up to 45,000 eggs while ''O. vulgaris'' clutches can include 500,000 eggs.<ref name="AZAmanual">{{cite web |url=https://www.aza.org/assets/2332/giant_pacific_octopus_care_manual_final_9514.pdf |title=Giant Pacific Octopus (Enteroctopus dofleini) Care Manual |publisher=AZA (Association of Zoos and Aquariums) Aquatic Invertebrate Taxonomic Advisory Group in association with AZA Animal Welfare Committee |date=9 September 2014 |access-date=31 May 2016}}</ref>{{rp|75}} Fertilised octopus eggs are laid as strings within a shelter.<ref name=Crowfootreproduction/><ref name=Mather/>{{rp|26}} Female giant Pacific octopuses nurture and protect their eggs for five months (160 days) until they hatch.<ref name=Crowfootreproduction/> In colder waters, such as those off [[Alaska]], it may take up to ten months for the eggs to completely develop.<ref name = "AZAmanual" />{{rp|74}} In the [[Argonaut (animal)|argonaut]] (paper nautilus), the female is much larger than the male. She secretes a thin shell shaped like a [[cornucopia]], in which the eggs are deposited and in which she also resides and broods the young while swimming.<ref name=Mather/>{{rp|26, 141}}

[[File:Fish3566 - Flickr - NOAA Photo Library.jpg|thumb|Octopus [[paralarva]], a [[plankton]]ic hatchling|alt=A microscopic view of a small round-bodied transparent animal with very short arms]]

Most young octopuses hatch as [[paralarva]]e,<ref name=Ruppert/>{{rp|363–365}} ''Octopus'' larvae in particular are [[plankton]]ic for weeks or months. Larvae feed on shrimp, isopods and [[amphipod]]s, eventually settling on the ocean floor to mature.<ref name=Wells/>{{rp|178}} Species that produce larger eggs instead hatch as benthic animals similar to the adults.<ref name = "AZAmanual" />{{rp|74–75}} These include the [[Southern blue-ringed octopus|southern blue-ringed]], [[Caribbean reef octopus|Caribbean reef]], [[California two-spot octopus|California two-spot]] and ''[[Eledone moschata]].''<ref>{{cite journal |last1=Forsythe |first1=J. W. |last2=Hanlon |first2=R. T. |title=A closed marine culture system for rearing ''Octopus joubini'' and other large-egged benthic octopods |journal=Laboratory Animals |year=1980 |volume=14 |issue=2 |pages=137–142 |doi=10.1258/002367780780942737 |pmid=7431823 |s2cid=19492476 |doi-access=free }}</ref>