German Sumbre of the Hebrew University in Israel and his colleagues analyzed a hundred videotapes of octopuses using their flexible arms to fetch food items. They found that the animals formed "quasi-joints" that resembled those of the shoulders, elbows and wrists of humans. When an octopus grasped a food reward with its suckers and brought it toward its mouth, these joints formed at points that divided the arm into three sections. Two of the sections were of similar lengths, which remained relatively constant over all the trials. The set-up is similar to the human arm, which has upper and forearms of roughly equal lengths, the scientists say.
There are a large number of ways for a flexible arm to transport food, so it is surprising that the octopus uses a method so similar to the limbs of animals with rigid skeletons, the authors note. Their findings, they conclude, suggest "that an articulated limb may provide an optimal solution for achieving precise, point-to-point movements."