Crinoids are marine animals that make up the class Crinoidea of the phylum Echinodermata. The name comes from the Greek word krinon meaning “a lily” and eidos, “form”. While there are only about 600 living species, they were much more abundant in the past. For example, during the mid- to late Paleozoic there are limestones that consist of crinoid fragments. Crinoids can live in water depts. From shallow to the bottoms of trenches at 30,000 feet (9,000 m). Some crinoids, commonly referred to as “sea lilies” are attached to the bottom during their adult phase by a stalk or stem that may be 3 feet (1 m) in length while most are unstalked and free-swimming called “feather stars” are unstalked and are free to move throughout the water column. The stem is attached to the body of the animal called the calyx that contains the animals digestive and reproductive organs with the mouth located at the top of the dorsal cup with the anus located peripheral to it. The calyx is surrounded by arms which number about ten while the arms of the free-swimming forms branch and may have as many as 200 branches. Crinoids feed by filtering particles of food from the sea water with the arms which are then passed along by cilia toward the mouth. The stalked crinoids affix themselves to the sea bottom by disc-like suckers that may continue outward from the base in the form of arms The long and varied geologic history of the crinoids demonstrates how well the echinoderms have adapted to filter-feeding.