Unusual seashell or something other ?

[ale.v]

I'm not understanding which is your problem.

Are you still in doubt with the classification?
Why?


Rember that the shape is not important, because it depends on the environment.

For the classification I follow this two steps:
1) The specimen is from Mediterrean see
2) The specimen has several "nubby" (hope the word is correct) lines, clearly visible in your pictures, in particular in the upper-right one.