Crinoid

Crinoids Temporal range: Ordovician–recent[1] PreꞒ Ꞓ O S D C P T J K Pg N
Crinoid on the reef of Batu Moncho Island, Indonesia
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Echinodermata
Subphylum:	Crinozoa
Class:	Crinoidea Miller, 1821[2]
Major groups
†Camerata Pentacrinoidea Articulata (700 living species) †Disparida †Porocrinoidea †Flexibilia

Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their juvenile form are commonly called sea lilies, while the unstalked forms, called feather stars^[3][4] or comatulids, are members of the largest crinoid order, Comatulida. Crinoids are echinoderms in the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers.^[5] They live in both shallow water^[6] and in depths as great as 9,000 meters (30,000 ft).^[7]

Adult crinoids are characterised by having the mouth located on the upper surface. This is surrounded by feeding arms, and is linked to a U-shaped gut, with the anus being located on the oral disc near the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, in most crinoids the five arms are subdivided into ten or more. These have feathery pinnules and are spread wide to gather planktonic particles from the water. At some stage in their lives, most crinoids have a short stem used to attach themselves to the substrate, but many live attached only as juveniles and become free-swimming as adults.

There are only about 700 living species of crinoid,^[8] but the class was much more abundant and diverse in the past. Some thick limestone beds dating to the mid-Paleozoic era to Jurassic period are almost entirely made up of disarticulated crinoid fragments.^[9][10][11]