I have lists of my favorites but if I had to choose one out of them it would be The Gloomy Octopus!
Octopus Tetricus, nicknamed The Gloomy Octopus for it's big droopy eyes!
It was originally thought to be a solitary species but they can actually be quite social and have been observed making dens within close proximity of each other!
In fact there are two octopus "cities" that have been discovered called Octopolis and Octlantis, the 2 sites are within a few hundred meters of each other and up to 14 octopuses have been observed living in one of these cities at once.
(Above is a picture of two gloomy octopuses from the Octopolis site)
Octopolis is made up of several dens and some human debris, namely a large cement block structure that has been seen with 3 octopuses nestled in the nooks at once. This led scientists to believe these octopus cities could only form with the condition of human structures, until they discovered Octlantis only a few hundred meters away from the original site, which was only made up from octopus-made dens.
The thing about gloomy octopuses is that they're ecosystem engineers, and what I mean by that is the way they interact with the environment around their den creates an active ecosystem.
(Video of an Octopolis resident cleaning it's den of shells)
When they make a den they often leave piles of discarded shells around, these shell piles create great hiding places for smaller prey that they can easily catch. These small fish attract larger fish, and the cycle builds. And it is absolutely incredible.
There's a lot to love about these guys and you will surely see me posting more of them on here!