hey flirt, hold hands and guard their lovers jealously -- yet they don't even have bones.

The love lives of octopuses are far more complex than anyone thought,

"Each day in the water, we learned something new about octopus behavior, probably like what ornithologists must have gone through after the invention of binoculars," said Huffard, now at the Monterey Bay Aquarium Research Institute in Moss Bay, California.

"We quickly realized that Abdopus aculeatus broke all the rules, doing the near opposite of every hypothesis we'd formed based on aquarium studies."

They saw male cephalopods guarding the dens of their mates for several days, warding off rivals and even strangling them if they got too close.

Small males would sneak in to mate by swimming low to the ground in feminine fashion and not displaying their "male" brown stripes, the researchers reported in the journal Marine Biology.