 The eight arms are thick , tapering to a narrow point . They are unequal in length , with arm pair I the shortest , followed by arm pair II and arm pair IV , and arm pair III the longest . All of them possess two rows of suckers . Each sucker has a diameter less than 2 mm ( 0 @.@ 08 in ) , decreasing distally , and a ring of 17 to 28 sharp acute teeth . The left arm of pair IV in males is modified into a sexual organ known as the hectocotylus . They bear long fleshy protrusions ( papillae ) with toothless suckers at the distal portion . The tentacles are thick and long , extending the length of the mantle when retracted . They are slightly compressed laterally . A prominent ridge ( a keel ) is present on the outer surface of each of the tentacle clubs ( the wide tip of the tentacles ) . There are four rows of suckers on the manus ( proximal part of the club ) and the dactylus ( distal part of the club ) . The larger suckers in the centre of the manus have 17 to 18 widely spaced teeth . 
