Hectocotylus

: hectocotyli) is one of the arms of male cephalopods that is specialized to store and transfer spermatophores to the female.

Although Aristotle knew of its use in mating, he was doubtful that a tentacle could deliver sperm.

The name hectocotylus was devised by Georges Cuvier, who first found one embedded in the mantle of a female argonaut.

Supposing it to be a parasitic worm, in 1829 Cuvier gave it a generic name (Hectocotyle),[2][3][4][5] which is a New Latin term combining the Greek words for "hundred" (hec(a)to(n)) and for "hollow thing, cup" (cotyle).

The shape of the tip of the hectocotylus has been much used in octopus systematics.