Biological screw joint
The biological screw joint is a naturally occurring form of the screw joint, a mechanical device that combines rotational movement with single-axis translation. Alexander Riedel of the State [Museum of Natural History Karlsruhe] and Thomas van de Kamp of the Karlsruhe Institute of Technology discovered it in specimens of Trigonopterus oblongus, a weevil found in Papua.
Discovery
Anatomical examination was made for specimens of the weevil species Trigonopterus oblongus, provided by the Karlsruhe State Museum of Natural History, using a microtomograph at the Institute of Synchrotron Radiation of Karlsruhe Institute of Technology. The analysis revealed that the weevils had a nut-and-screw system for the hip-leg joint.Mechanism
The mechanism has been described as "rotational movement combined with a single-axis translation".The arthropod hip–leg joint consists of two parts – the coxa and the trochanter. The coxa, in the case of weevils, resembles a nut, and it has a thread running along its inner surface with an angular span of 345°. The trochanter resembles the screw. It is rod-shaped with a large external spiral flange, having an angular span of 410°, in excess of a full circle, which functions as a thread. When the leg muscles of a beetle are stretched, the screw turns. Though the screw-thread provide for very large angular rotation, the front legs of weevils are capable of rotating by 90°, while their hind legs can rotate by 130°.
The weevils are just long and can fold their legs below their body. The joint is just in size. Before this was discovered, all known hip-leg joints have been based on either the ball and socket joint system for hip-leg connections, as in humans, as hinges or as saddle joints. The discovery is the first ever instance of a musculoskeletal nut-and-screw system in the animal kingdom.