The horsehoe crab because it was one of the first animals to ever live on earth
The way that you will easily deduce which one it is is that you'll see the mouth first instead of the anus because of the different ways of development.
Motor unit refers to the functional element of muscle contraction during an exertion. There are two basic types of motor unit: large and small motor units. During low to moderate level exercise, small motor units are activated. Small motor units are recruited during sustained activity; is made up of high proportion of type 1 muscle fibers, which are resistant to fatigue
The type of evolutionary mechanism that occurred was natural selection
