arm hectocotylus Taxon notes: Among Decapodiformes (ten-limbed cephalopods), generally either one or both of arms IV are hectocotylized; in incirrate octopuses it is one of arm pair III.[1] Many coleoids lack hectocotyli altogether.[1] The shape of the tip of the hectocotylus has been much used in octopod systematics. In many species it is considerably elaborated. However, in the males of some species, such as the Seven-arm Octopus (Haliphron atlanticus), the hectocotylus develops in an inconspicuous sac in front of the right eye that gives the male the appearance of having only seven arms The modified arm in males used for transferring spermatophores to the female. In incirrates the hectocotylus is one member of arm pair III while in decapodiforms frequently one or both members of arm pair IV are modified. Many species of coleoid cephalopods lack a hectocotylus. http://upload.wikimedia.org/wikipedia/commons/thumb/9/99/Hectocotylized_arm_of_a_squid.jpg/189px-Hectocotylized_arm_of_a_squid.jpg hectoctylized arm intromittent organ