Arthropod leg

Arthropod legs are paired appendages extending from the segments of the arthropod body, primarily used for locomotion, but also modified for various other functions. The basic structure of an arthropod leg consists of a series of articulated segments, connected by flexible joints, allowing for a wide range of movement.

The precise number and type of segments vary considerably across different arthropod groups. However, a common ancestral pattern, observable in many crustaceans and insects, involves segments called the coxa, trochanter, femur, tibia, and tarsus (which itself may be further subdivided into tarsomeres). Other segments, such as the basis and ischium, are present in some groups.

The articulation points, or joints, between these segments are crucial for leg movement. Muscles attached to the inner walls of the exoskeleton exert force across these joints, enabling complex movements such as walking, running, jumping, swimming, digging, and grasping.

Legs can be highly specialized depending on the arthropod's lifestyle. For example, mantis legs are modified for grasping prey, while bee legs are adapted for collecting pollen. Aquatic arthropods may possess legs modified into swimming paddles. Some arthropods use legs for sensory perception, with structures such as chemoreceptors and mechanoreceptors located on the legs. Loss of a leg is not necessarily permanent; many arthropods possess the ability to regenerate lost limbs.

The number of legs is also a distinguishing characteristic between arthropod groups. Insects possess six legs (three pairs), while arachnids have eight legs (four pairs). Myriapods, such as millipedes and centipedes, possess numerous legs, varying greatly in number between species. Crustaceans exhibit significant variation, with the number of legs depending on the species and body region.