Thanks for the explanation Camille. It's a pity that the spine isn't visible in my photo. I found a photo of the spine on internet. http://www.biolib.cz/en/image/id114654/
I have seached on internet for I did not know the word Amblypygi. I found whip spiders and tailless whip scorpions. Interesting animals, but I think It is the stubby backside!?