Octopuses have no built-in shell, unlike other mollusks, such as snails and mussels. To protect themselves, they often squeeze into small spaces.
Here, a female larger Pacific striped octopus hangs out of her shell. In this moment, captured by the camera, she was observing a male, who was approaching her from the right.
During the study, the octopuses could establish their own shells/dens. One pair became so close, however, that they chose to share a den for more than three consecutive days at a time. They did this more than once, too.
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