How did the crab evolved its appendages?

Question

How did the crab evolved its appendages?

Answer 1

Evolving appendages in crabs ( and all other species belonging to phylum arthropods) and not only, also body segments and legs are the signs of better adaptations for any species belonging to that group.

Just compare earthworms, they have segmented body but no legs neither appendages. So, crabs classified a little above adapted (evolved) class than earthworms.

And if you compare other species from any lower group or class and then step to step go to  upper class species, you would notice adaptation factors  are better as you go higher.

An example is- mammals and particularly humans, the most functional, developed and evolved species than any other.

Perhaps you know the appendages are used in crabs for feeding purposes. So, a various types of organs that have evolved are meant for " Better life function processes. And the more developed the species is , the better are their evolved organs or body systems.

http://www.geology.wisc.edu/~museum/old/...

See this site for a comparison of other species in the same phylum.....

Answer 2

Arthropods came from annelid ancestors.

You may have seen parapodia in Nereis.

Evolution of limbs( biramous) has been a gradual process.