Echinodermata

	Mineralogy	Geologic Range	Habitat	Ecology	Examples
blastoids	lo-Mg calcite	Silurian - Permian	benthic marine	filter feeder	Pentremites
crinoids*	lo-Mg calcite	Ordovician - Recent	benthic marine	filter feeder	sea lillies
asteroids*	lo-Mg calcite	Ordovician - Recent	benthic marine	various heterotrophe	star fish
ophiuroids*	lo-Mg calcite	Ordovician - Recent	benthic marine	various heterotrophe, usually deposit feeder	brittle stars
echinoids*	lo-Mg calcite	Ordovician - Recent	benthic marine	various heterotrophe	sea biscuit, sea urchins, sand dollars
holothurians*	lo-Mg calcite	Ordovician - Recent	benthic marine	various heterotrophe	sea cucumbers
rhombiferans	lo-Mg calcite	Ordovician - Devonian	benthic marine	UNK, heterotrophic
diploporitans	lo-Mg calcite	Ordovician - Devonian	benthic marine	UNK, heterotrophic
eocrinoids	lo-Mg calcite	Cambrian - Silurian	benthic marine	UNK, heterotrophic
edrioasteroids	lo-Mg calcite	Cambrian - Pennsylvanian	benthic marine	UNK, heterotrophic	seat stars

* Extant taxa

Ranges of major echinoderm groups

Phylum Echinodermata
.....Superphylum Crinozoa
..........Class Crinoidea (Cambrian - Recent, 1005 genera)
..........Class Paracrinoidea (Ordovician - Silurian, 13-15 genera)
.....Subphylum Blastozoa
..........Class Blastoidea (Silurian - Permian, 95 genera)
..........Class Rhombifera (Ordovician - Devonian, 60 genera)
..........Class Diploporita (Ordovician - Devonian, 42 genera)
..........Class Eocrinoidea (Cambrian - Silurian, 30-32 genera)
..........Class Parablastoidea (Ordovician, 3 genera)
.....Subphylum Asterozoa
..........Class Asteroidea (Ordovician - Recent, 430 genera)
..........Class Ophiuroidea (Ordovician - Recent, 325 genera)
.....Subphylum Homalozoa
..........Class Stylophora (Cambrian - Devonian, 32 genera)
..........Class Homoiostelea (Cambrian - Devonian, 12-13 genera)
..........Class Homostelea (Cambrian, 3 genera)
..........Class Ctenocystoidea (Cambrian, 2 genera)
.....Subphylum Echinozoa
..........Class Echinoidea (Ordovician - Recent, 765 genera)
..........Class Holothuroidea (Ordovician - Recent, 200 genera)
..........Class Edrioasteroidea (Cambrian - Pennsylvanian, 35 genera)
..........Class Edrioblastoidea (Ordovician, 1 genus)
..........Class Helicoplacoidea (Cambrian, 3 genera)
..........Class Cyclocystoidea (Ordovician - Devonian, 8 genera)

Subphylum Crinozoa (Cambrian-Recent) Crinoids, which are commonly called "sea lilies", are benthonic passive filter-feeding echinoderms. Contrary to popular belief, they are not extinct - several hundred species of stalked and unstalked crinoids inhabit the modern world's oceans. The stalked forms inhabit the deep oceans, and thus are not regularly seen except by submersibles (a cheaper way to view crinoids is to rent the movie The Abyss - which correctly shows a sea floor inhabited by crinoids), while stalkless forms are commonly found in shallower depths (including the shallows of coral reefs). Crinoids have a compact calyx (body) with long, erect, mobile arms. The arms support smaller, feather-like structures called pinnules which form the filtration fan which crinoids use to feed. The food is transferred down the arms to the mouth by tube feet located on the pinnules and arms. The oral side of the calyx therefore faces the filtration fan, and the anus is also located on the oral side of the calyx - and thus also faces toward the filtration fan. The calyx is usually connected to the bottom via a stem composed of stacked, articulated plates called columnals. Stemmed forms frequently have a holdfast composed of small, polygonal plates, although some species wrapped their stem around other organisms, and thus didn't need a holdfast.

Ranges of major crinozoan groups

Subphylum Blastozoa

Blastozoans are an extinct group of mostly stemmed echinoderms. They had delicate arm-like brachioles coming off their ambulacra, and a complex internal respiratory system which differentiates the blastozoan classes from other echinoderms. The morphology of the blastozoans has led some workers to suggest that the blastozoans lacked tube feet, and thus possibly a water vascular system - another feature which would differentiate them from all other echinoderms. However, this theory is still controversial.

Ranges of major blastozoan groups

Subphylum Asterozoa

Asterozoans express the classic pentameral symmetry of echinoderms. Each armin the living asterozoan contains a radial branch of the water vascular system, which supports numerous paired tube feet which extrude through the underside of each arm. These tube feet form the ambulacra and are located in the middle of each arm along a features called the ambulacral groove. In many echinoderms, this groove carries small captured food particles to the mouth of the organism, although in some types the feature has been altered to serve other functions. The mouth is located where the radiating ambulacra intersect. The side with the mouth in echinoderms is defined as the oral side. The side opposite is called the aboral side. Depending on the group, the oral side can point up or down (in asterozoans, it points down). The water vascular system maintains communication with the ambient sea water through a group of pores in the madreporite, which in asterozoans is located on the aboral side, and can be easy to spot in some species (it looks like a drain cover in a sink). Like most echinoderms, the skeleton of asterozoans is composed of numerous small calcite plates called ossicles which readily disarticulate upon the animal's death.

Ranges of major asterozoan groups

Subphylum Asterozoa Class Asteroidea (Ordovician-Recent) Asteroids are asterozoans whose internal body parts extend into the arms. Unlike the ophiuroids, there is no sharp distinction between the arm structure and the central body structure. Most asteroids are predatory, preying on clams, corals, other echinoderms, or anything else unlucky enough to cross their path. Some asteroids can extrude their stomach through their mouth, killing and partially digesting their prey outside their body. Asteroids are among the most active echinoderms.

Subphylum Asterozoa Class Ophiuroidea (Ordovician-Recent) Ophiuroids, or brittlestars, are asterozoans with a central body disk which contains all of the viscera. The arms of ophiuroids are muscular extensions and contain only the ambulacra. Many ophiuroids are scavengers, and will eat just about anything. Along with crinoids and holothurians, ophiuroids essentially rule the floor of the deep oceans, although they are also found in shallower depths.

Subphylum Echinozoa

Echinozoans include the familiar sea urchins, sea biscuits, and sand dollars, as well as several obscure Paleozoic groups, and the unusual sea cucumbers. Except for sea cucumbers, echinozoans have a globose or discoidal test with 5 ambulacral regions. They lack free arms like those possessed by starfish and crinoids, and use spines and/or elongate tube feet for locomotion.

Ranges of major echinozoan groups

Subphylum Echinozoa Class Echinoidea (Ordovician-Recent) Echinoids are a large and widespread group of echinozoans with a good fossil record in Mesozoic and Cenozoic strata. They have globular to flattened tests composed of a large number of plates, and live free on and in the sea floor. Common echinoids include urchins, sand dollars, and sea biscuits. There are two main types of echinoids: regular echinoids which live on the sea floor, and irregular echinoids which are burrowers. Morphology of echinoids

Kier, P.M. 1974. Evolutionary trends in post-Paleozoic echinoids. Journal of Paleontology Memoir 5, 48.

Nichols, D. 1969. Echinoderms, 4th edition. Hutchinson and Co., London.

Smith, A. 1984. Echinoid palaeobiology. Special Topics in Palaeontology, Allen and Unwin, London.

Sprinkle, J. 1973. Morphology and evolution of blastozoan echinoderms. Harvard University Museum of Comparative Zoology Special Publication. Cambridge.

Sprinkle, J. and Kier, P.M. 1987. Phylum Echinodermata. in Boardman, R.S., Cheetham, A.H., and Rowell, A.J., (eds.). Fossil Invertebrates. Blackwell Scientific Publications. 713 pp.