Strange "thing" on my crab apple leaves

I just noticed spots on my crab apple leaves.From the top looks like yellow circle. From the bottom like spikes? Pests? Fungus? Never seen such thing. Any help will be appreciated. Thanks.

I think it's a gall, potentially caused by Cedar Apple Rust.
http://blog.planetnatural.com/pest-problem-solver/plant-disease/cedar-apple-rust/

Looks like what I had on my pear last summer:

Questions about pear rust

Thank you so much Tom and Chris. It's clear enough. Can I use Bordo or has to be Bonide?

Just remove and destroy the leaf or leaves.

A spraying with lime sulfur in late spring will help reduce the likelihood of infection. Keep the tree a long way away from junipers (but if they grow all around you like here, you just learn to live with it).

Cedar apple rust (and other rusts of members of the rose family) isn't a serious problem. Just destroy affected leaves.

Thanks Jim. I just burn all affected leafs. Will give lime sulfur spray soon.

I had this several years ago on a crab apple...it sure looks malignant!

Those things sticking out are spores. They will infect junipers. The year after next, the junipers will infect apples.
Lime sulphur will do nothing at this stage. In the winter, spray with lime sulphur or dormant oil. For next year, ask your extension agent for the spraying schedule.
Iris

Thank you Iris. Such annoying thing this galls.