Understanding Evolution

Jointed legs

We've seen that arthropods all have bilateral symmetry, segmented bodies, and hard exoskeletons. Another character inherited by all arthropods is jointed legs.

How to Bend a Hard Exoskeleton
Having a hard exoskeleton introduces a problem for arthropods: flexibility. How can an animal with a rigid body covering move its legs? Evolution solved this problem with joints. All arthropods (arthro = joint, pod = foot) have jointed limbs.

In most of the leg, the exoskeleton is hard, but at the joints it is softer and bendable, allowing movement in the same way that a suit of armor does. The limb can be controlled by contracting muscles connected to the exoskeleton on both sides of the joint.

Try it out!
Which of these animals have jointed legs?

 

View this article online at:
http://evolution.berkeley.edu/evolibrary/article/arthropods_07

Understanding Evolution © 2015 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California