It's a tough one John. Whether the Tremoctopus male is as small (relative to the female) as popularised, or whether the male Ocythoe is even smaller than the enormous [and presposterously ugly] female could be debated (but who really cares; biggest/smallest; never any prize for being the second smallest).
In both genera, and the related Argonauta, the male's third right (or left) arm detaches and swims (????) to/into the female's mantle cavity. In Argonauta I think I recorded up to 6 (maybe 7) detached hecotlyii (whatever the plural of hectocotylus is).
A joke I often use in talks (serving also to wake up an audience) is to pretend to be the comparatively minute male, bumping into the female in the dark, and letting out a loud shriek (pretending to be the male, totally startled by the female's size and shear ugliness). In this moment of terror I jettison my reproductive arm (beats being eaten by the female doing it the 'conventional way'), and escape. Of course I have not encountered any male in collections that had jettisoned the arm (in all the arm was intact); kind-of makes you wonder why jettison it, if doing so is to escape being consumed, when death would appear to be imminent anyway (what's worst: death by female, death by bleeding, or death by sensescence? Nobody need answer.).
I don't tell the story often (it's a bit sad), but many years ago when trawling (bottom trawling, sadly) on scampi grounds in the Bay of Plenty (north-eastern NZ), a female Argonauta nodosa was retained in the trawl. Working in museums most of my (cough) adult life, and having spent an inordinate amount of time reconciling (or at least trying to) morphologies of squid and octopus fixed with different preservation histories, it was important to fix this animal without freezing it first (as all others that I'd handled had been frozen, then defrosted). Believing the female Argonauta to be dead, I placed it directly into a 5% formalin/seawater solution, injecting also into the viscera (freezing it would have lost valuable systematic characters). I could not believe what I saw - THREE detached hectocotylii (there's that difficult plural again) swam from the dead female's mantle and writhed around in the bottom of the bucket (even without a 'brain', and fully functioning circulatory ststem, and no, as far as can ascertain, alimentary system, these 'arms' live for some time).
Even when detached from the male (usually lodged around the base of the female's gill), the hectocotylus is still 'live'. Why the male ditches it (instead of 'gently transferring' genetic material via a conventional hectocotylus) is an unknown, especially if death is imminent. We really don't know a lot about these animals.
Why the male is smaller? Hmmmmm. The same seems to be true of ammonites (I believe), and seems to be the rule in cephalopods. Quite unfair I believe.
). Is it possibly because those males that 'waste' energy in [excess] growth lose out reproductively to those that mature early and go about their business ASAP, and who therefore leave more offspring, causing eventual selection for individuals who mature earlier/at smaller sizes? 
