The blanket octopus

Yikes:

The male blanket octopus spends his existence drifting along waiting to meet with a female. If the male meets a female, he fills one of his tentacles with sperm and tears it from his body. He gives this sperm-filled tentacle to the female which she then uses to fertilize her eggs. Afterwards, the female leaves the male who floats away and dies.

Double yikes:

An unusual defense mechanism in the species has evolved: blanket octopuses are immune to the poisonous Portuguese man o' war, whose tentacles the female rips off and uses later for defensive purposes.