Crinoids.

Crinoids are Echinoderms, thus related to starfish, sea urchins, sand dollars. Like these familiar creatures, they also have 5-point radial symmetry and lived in the sea. Crinoids typically look like a feather-duster on a stalk (think of an upside-down starfish with a stalk on its back). Link to information and photos of living crinoids on Wikipedia.

A few hundred species of crinoids exist today, but in the past, they were much more abundant. Around Las Vegas, fossil crinoids can be found in carbonate rocks dating from the Ordovician Period (about 485 million years ago) forward.

For the most part, we find individual stem segments, looking somewhat like a white, life-saver candy, but sometimes we find short stem fragments too.