A prefix meaning combined, like in arthropathy and arthroscopic. Before a vowel, it becomes arthr-, such as arthralgia and arthritis. Through the Greek word arthron for joint. Eventually from an Indo-European root meaning to join or even fit together.
word-forming factor meaning "pertaining to your joints," from Greek arthro- (before vowels arth-), comb. kind of arthron "shared," from PIE *ar-dhro-, from *ar- "to suit together;" see supply (n.1).
There are a number of other important points of structure besides those referring to the somites and appendages in which Limulus agrees with Scorpio or other Arachnida and differs from other Arthro- '11'1 poda.