How octopus mate
The third arm of many male octopus species is specially modified for transferring packets of sperm (spermatophores) to the female. During mating the male inserts his modified arm into the female’s mantle. Sperm packets are released through his funnel into a groove on his modified arm, from where they are guided to the female’s reproductive organs.
Some open-ocean octopus have a unique form of reproduction. This is true of the paper nautilus (these are not true nautilus, but a species of octopus named because their shell appears similar to that of a Nautiloid). The tiny male’s modified arm breaks off during mating, and through some unknown process navigates its way into the female mantle cavity, taking residence around her gills and eventually releasing its sperm. Males are assumed to die after mating. The blanket octopus (Tremoctopus violaceus), known from the Tasman Sea, exhibits the most extreme form of sexual size difference, with females being 40,000 times heavier than males.
How squid mate
One or more arms of many squid species is modified for reproduction, transferring a sperm packet to females in a similar way to octopus. For those squid species lacking modified reproductive arms, the male often has a grossly enlarged penis that it uses like a giant syringe to thrust spermatophores into various parts of the female’s mantle, head or arms. Male scaled squids (Lepidoteuthis grimaldii) also possess two sabre-like hooks, which they stab into the larger, slippery females during mating.
Most octopus species deposit eggs directly onto the sea floor, but some open-ocean species brood their eggs in their mantle or around their mouth. The shell of the paper nautilus is really an egg case and brood chamber, secreted only by the female and in which she lays her eggs. Shallow-water species generally produce many small eggs that develop into hundreds, if not thousands of tiny plankton-feeding young. Deep-sea species produce fewer, larger eggs, and their young hatch and commence life as miniature adults, crawling around the sea floor.
Most squid release large, free-floating gelatinous egg masses – up to 2 metres in diameter in the case of arrow squid (Nototodarus gouldi) – each containing thousands of eggs. A few species discharge tiny, individual eggs. Females of some deep-sea squid species brood their eggs in their arms. The coastal-dwelling broad squid (Sepioteuthis australis) attaches strands of white, grape-like eggs to seaweed.
Scientists count the rings on two tiny skull bones (statoliths) in a squid’s head to determine its age. Some shallow-water species deposit these rings on a daily basis, but it is not certain whether the same applies for deeper-water species. If it does, then giant squid (Architeuthis) would be only 480 days old – a staggering growth rate, given that this squid hatches from an egg only 2 millimetres in diameter and grows to 13 metres in length.
The majority of squid and octopus hatch as miniature adults. Several exceptional squid species have a larval stage that undergoes a distinct metamorphosis to the adult form.
As squid have proven exceptionally difficult to keep in captivity, studies of longevity are extremely rare. Most octopus and squid species are thought to live for only a single year, and die after mating.