Crinoids appeared in the oceans in the Early Ordovician Period, 480 million years ago, and thrived throughout the Palaeozoic Era. Thy are an unusually beautiful and graceful kind of sea animal and are among the most ancient and primitive of ocean invertebrates. The creature can resemble that of an underwater flower growing on thick stems with some parts that look and act like roots anchoring them to the ocean floor; sometimes they are called sea lilies. Other varieties have no stalks or root like parts and are commonly known as feather stars and move about on tiny hook like structures called cirri. Crinoids are echinoderms, with the flower part being the arms that catch its food; attaching themselves to the bottom of the sea floor or a rock or a piece of wood with the root-like hold fast. 
Crinoids fossilize readily and so there is an abundance of them to be found, mostly stalk fragments, finding them as a whole creature is extremely rare and very uncommon. There are 2 reasons that they fossilize so easily; one, the ocean floor is a good environment for fossilization to occur; and two, their skeletons are made of calcareous plates. This is a hard rock like material. Almost all varieties of crinoids have been extinct since the end of the Triassic period, but a few species exist to this day, mostly in deep sea and there are more than 600 living species known to science.
