Cuantos meridianos hay en el mundo

The question asks "How many meridians (of longitude) are there
in the world ?"

That's like asking "How many marks are there on a 1-foot ruler ?"
The answer depends on what divisions the manufacturer decided to
mark on his rulers. Whole inches only ?  Half inches ?  Quarter inches ?
Tenths of an inch ?  Sixteenths of an inch ?

On the Earth, there are 360 degrees of longitude all the way around.
Some maps and globes print a meridian every 10 degrees, some print
one every 15 degrees, some print one every 30 degrees, and some don't
have any meridians at all printed on them.

On the mapping software I use, I get to choose how close together I want
the meridians printed on my maps.  If I want them, I can see a meridian every
2-seconds of longitude, giving me  648,000 meridians on the screen. 

(I've never needed all of them.  I tried it once, but there were so many
meridians printed on my maps that all the actual places were covered up.)