Female and male anglerfish become one (fuse tissues and share vital systems), possibly forever, to mate - at the cost of immunity
So romantic, no.

I've heard there's a penguin-related knowledge deficiency in this forum:
Math of the Penguins
"Though dominant winds can appear to push a huddle along the ice, the truth is more nuanced. Blanchette and his team’s model made clear that the birds do not move in unison. Penguins in the huddle’s center, where temperatures reach a sweltering 100 degrees Fahrenheit, mostly stand still. A bird who finds himself on the huddle’s windward side is soon driven to relocate to its warmer, leeward side. As more birds leave the windward side, penguins in the center soon find themselves exposed. In due course, these penguins also depart for the leeward side. 
Huddles typically last a few hours, during which the penguins may cycle through multiple rotations from the huddle’s cold exterior to its warm interior. In the process, each individual prioritizes his own warmth, yet the huddle’s heat is shared by all. 
Penguins seem to know what mathematicians learned long ago: The densest packing of shapes on a plane is a hexagonal grid."

“Insofar as she recognized at all that she was dreaming, she realized that she must be exploring her subconscious mind. She had heard it said that humans are supposed only to use about a tenth of their brains, and that no one was really clear what the other nine tenths were for, but she had certainly never heard it suggested that they were used for storing penguins.”

— Douglas Adams, “The Long Dark Tea-Time of the Soul”

That's no brainer. The penguins are there to cover bad memories. In the light of article's discovery of the optimal hcp packing of huddling penguins, it is a very wise choice of species. I use cats because my FLUF (feeling Larry utility function) has a factor for soft fur. My every bad memory is covered by a cat or a few. Every time I remember something accidentally, I see the cats. After some time all I remember are the cats. There are side effects obvi... MEOWW!!!

How whales sleep?
TL;DR: Zzzz...

Two of our beehives slipped from their foundations and fell into the moat. No survivors.