Hectocotylus

Anatomy

Variability

• Many coleoids lack hectocotyli altogether.
• Among Decapodiformes, generally either one or both of arms IV are hectocotylized.
• In incirrate octopuses it is one of arm pair III. Rare examples of double and bilateral hectocotylization have also been recorded in incirrate octopuses.
• In male Seven-arm Octopuses, the hectocotylus develops in an inconspicuous sac in front of the right eye that gives the male the appearance of having only seven arms.
• In argonauts, the male transfers the spermatophores to the female by putting its hectocotylus into a cavity in the mantle of the female, called the pallial cavity. This is the only contact the male and female have with each other during copulation, and it can be at a distance. During copulation, the hectocotylus breaks off from the male. The funnel–mantle locking apparatus on the hectocotylus keeps it lodged in the pallial cavity of the female.