This is probably true of all the cephalopods ( cuttlefish, squids, octopuses, nautili etc
see here and here . . .
http://en.wikipedia.org/wiki/Octopus
http://answers.google.com/answers/threadview?i d=330161
"In the octopus and many cephalopods, the males have a special tentacle with which they insert their spermatophores under the mantle of the female. The tentacle is then retracted for future use.
The male paper nautilus is more profligate with its tentacles ... His spermatophore-bearing tentacle detaches itself from the body and swims -- under its own power -- to the female, being in effect a swimming penis."