My fossil hunting friend came across this object in a creek in eastern Missouri. At first glance this ~1 cm diameter ball with stout spikes would seem to be some sort of camerate crinoid, but the spikes cover the entire surface, with no apparent place to put arms, column, mouth, or anus. (Side note: That must be the crinoid folksong community's version of "Head, Shoulders, Knees, and Toes.") From there my fallback would be coral, or perhaps sponge, but the complete coverage around the whole sphere (see attached video) has me a bit baffled.
The creek flows through mostly Meramecian