The female of this octopus can be 40,000 times heavier than the male

Blanket octopuses show one of the most extreme size differences between sexes of any animal on Earth: females can grow up to two meters long, while males stay smaller than a walnut. Males also carry a detachable mating arm that breaks off inside the female and keeps fertilizing her eggs after he's gone. Females are additionally immune to the deadly sting of the Portuguese man o' war and will rip off its tentacles to use as weapons.

— Wikipedia contributors, Blanket octopus — Tremoctopus sexual size dimorphism