looks like an etiolated mammilaria to me

Hmmm, yes, I searched through cactaceae.net and could not find any Echinocereus plants that looked like the one you have. The distinct lack or ribs means it does not look like one to me.
Maybe it is as GL says?

I think it's probably a mamm too, but I don't think it looks etiolated at all.

cd

I agree that the plant looks very tubercular and lacks prominent ribs, but I think that's just because its still a baby. Look at the newest growth, the ribs are developing and it is not at all mamm-like. I can believe it is a baby Echinocereus but can't offer a species.

Hey Cesar, it has the spine colour of my Echinocereus laui, but at even at a young age this has didtinct ribs.
I must say though, that it looks very "Mammillific!", spine colours are reminiscent of M. fraileana, but that has hooked spines, or even M. viperina.
It'd be interesting to see what it's like after growing in some full light for a while.

CP

Hola:
Thanks by your opinions. I only can say that etiolated not is.It receives light sifted of the sun.

César