Although mating has never been observed in giant squid, it is thought that what happens is that the male injects his sperm packages into the female's arms. The process is likely to be a fairly violent affair as the female is probably not that keen on being injected. This is a problem for the amorous male as females are normally a third bigger than they are.
But males get round their inferior size by being endowed with a particularly long penis, which means they can inject the female without having to get too close to her chomping beak. The male's sexual organ is actually a bit like a high-pressure fire hose and is normally nearly as long as his body - excluding legs and head.
But having such a big penis does have one drawback: it seems that co-ordinating eight legs, two feeding tentacles and a huge penis, whilst fending off an irate female, is a bit too much to ask, and one of the two males stranded on the Spanish coast had accidentally injected himself with sperm packages in the legs and body. And this does not seem to have been an isolated incident since two of the eight males that had stranded in the north-east Atlantic before had also accidentally inseminated themselves.
It is also possible that the sperm packages had come from other males that they had 'bumped' into, in the dark depths of the ocean. However, the sperm packages ended up in the squid - it is just another part of the mysterious lives of these creatures of the deep sea.
Many spiders exhibit sexual dimorphism as well, typically with the female much larger than the male. In spiders of the genus Tidarren, this trend is carried to an extreme, with males that may be 1% of the female's size. Here's a photo of one of these little guys clinging to his girlfriend's underside, copulating frantically (there is cause for hurry, since she might decide to eat him). [...]
Shortly after the adult molt, male T. sisyphoides trap one in a bit of spider silk and twist it off. Voluntarily. A kind of willing hemipenectomy. One has to cringe at the thought, but I suppose I can sympathize -- if I had a pair of penises the size of volleyballs and weighing 10 pounds each attached to my cheeks, I might want to get rid of one, too.