In several deep-sea anglerfish species, the tiny male u2014 often a fraction of the female’s size u2014 bites into her body and never lets go. Over time their tissues and blood vessels fuse, and the male becomes little more than a permanent sperm supply.
An answer to scarcity
Finding a mate in the near-total darkness of the deep ocean is rare enough that some species evolved to never let go of one once found. It is strange by our standards and elegant by evolution’s.