If you want to know which place an octopus has in the sea, you should take a close look at the animals' skin.
According to a study, the species of Graneledone pacifica are the more warty the deeper they live in the sea. Researchers around Janet Voight from the Field Museum in Chicago report this in the Bulletin of Marine Science.
The team has studied 50 very different-looking deep-sea octopuses from the North Pacific. First, the researchers examined whether the genome was one or several species. Then they surveyed the size and compared the warts as well as the suckers of the animals.
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The octopuses came either from aquariums and zoological collections or had been captured at depths of 1116-2850 meters using manned submarines near the US coast.
The deeper the animals live, the smaller they are
The result of the comparisons: all the octopuses in the study had very similar genetic material despite the different appearance and belonged to the species Graneledone pacifica. But the deeper the animals lived in the sea, the smaller they were, the fewer suckers they carried on the tentacles, and the warmer they were.
The decreasing size of the researchers lead the researchers back to the lower food supply. "These animals have to work harder to find something to eat," says Voight. "And that means that at the end of their lives, they are smaller than others who have more food."
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Even the eggs of those animals that live in extreme depths are smaller. On the other hand, the difference between smooth and warty skin can not be explained biologically. "The reason for this difference remains a mystery," write Voight and colleagues.
Cuttlefish belong to the cuttlefish. They are related to snails or shells. The animals can bring their bodies into almost any shape. They have a relatively large brain that can solve complex tasks. This allows the animals to open screw caps, for example.