| Cystoidea Temporal range: | |
|---|---|
 | |
| "Cystoidea" from Ernst Haeckel's Kunstformen der Natur , 1904 | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Subphylum: | |
| Class: | †Cystoidea von Buch 1846 |
Cystoidea is a class of extinct crinozoan echinoderms, termed cystoids, that lived attached to the sea floor by stalks. They existed during the Paleozoic Era, in the Middle Ordovician and Silurian Periods, until their extinction in the Devonian Period.
Cystoids are distinguished from other echinoderms by triangular pore openings.
Superficially, cystoids resembled crinoids, but they had an ovoid, rather than cup-shaped, body. The mouth was at the upper pole of the body, with the opposite end attached to the substratum, often by a stalk, although some stalkless species did exist. The anus lay on the side of the body.
Five, or less commonly three, ambulacral areas ran along the outside of the body, radiating outwards from the mouth. A number of small tentacles either surrounded the mouth, or projected outwards in a row from the ambulacral areas, depending on species.
The most distinctive feature of cystoids was the presence of a number of pores in the rigid skeleton encasing the body. These were most likely respiratory in nature, allowing fluid to flow in or out of the body. In some species, the pores were clustered in distinct regions, but in others they were distributed quite widely over the body surface. See also List of echinodermata orders.
An echinoderm is any member of the phylum Echinodermata of marine animals. The adults are recognizable by their radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Adult echinoderms are found on the sea bed at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7,000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are the largest phylum that has no freshwater or terrestrial members.
Crinoids are marine animals that make up the class Crinoidea, one of the classes of the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. Those crinoids which, in their adult form, are attached to the sea bottom by a stalk are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, being members of the largest crinoid order, Comatulida.
Sea urchins are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone — from the intertidal seashore down to 5,000 metres. The spherical, hard shells (tests) of sea urchins are round and spiny, ranging in diameter from 3 to 10 cm. Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. Although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. In the food chain, the predators who eat sea urchins are the sea otter and the starfish, the wolf eel, the triggerfish, and human beings.
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as asteroids due to being in the class Asteroidea. About 1,900 species of starfish occur on the seabed in all the world's oceans, from warm, tropical zones to frigid, polar regions. They are found from the intertidal zone down to abyssal depths, at 6,000 m (20,000 ft) below the surface.
Entoprocta, or Kamptozoa, is a phylum of mostly sessile aquatic animals, ranging from 0.1 to 7 millimetres long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that draw food particles towards the mouth, and both the mouth and anus lie inside the "crown". The superficially similar Bryozoa (Ectoprocta) have the anus outside a "crown" of hollow tentacles. Most families of entoprocts are colonial, and all but 2 of the 150 species are marine. A few solitary species can move slowly.
Sea cucumbers are echinoderms from the class Holothuroidea. They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothurian species worldwide is about 1,717, with the greatest number being in the Asia-Pacific region. Many of these are gathered for human consumption and some species are cultivated in aquaculture systems. The harvested product is variously referred to as trepang, namako, bêche-de-mer, or balate. Sea cucumbers serve a useful role in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter, after which bacteria can continue the decomposition process.
The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet, causing them to extend and push against the ground, then relaxing to allow the feet to retract.
Brittle stars, serpent stars, or ophiuroids are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens.
Blastoids are an extinct type of stemmed echinoderm, often referred to as sea buds. They first appear, along with many other echinoderm classes, in the Ordovician period, and reached their greatest diversity in the Mississippian subperiod of the Carboniferous period. However, blastoids may have originated in the Cambrian. Blastoids persisted until their extinction at the end of Permian, about 250 million years ago. Although never as diverse as their contemporary relatives, the crinoids, blastoids are common fossils, especially in many Mississippian-age rocks.
Edrioasteroidea is an extinct class of echinoderms. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrates.
Articulata are the only extant subclass of the class Crinoidea. The group includes "sea lilies" and "feather stars". The Articulata are differentiated from the extinct subclasses by their lack of an anal plate in the adult stage and the presence of an entoneural system.
The stylophorans are an extinct, possibly polyphyletic group allied to the Paleozoic Era echinoderms, comprising the prehistoric cornutes and mitrates. It is synonymous with the subphylum Calcichordata. Their unusual appearances have led to a variety of very different reconstructions of their anatomy, how they lived, and their relationships to other organisms.
The Eocrinoidea are an extinct class of echinoderms that lived between the Early Cambrian and Late Silurian periods. They are the earliest known group of stalked, arm-bearing echinoderms, and were the most common echinoderms during the Cambrian.
Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms, prehistoric marine invertebrates. They are also referred to as carpoids.
The Asterozoa are a subphylum in the phylum Echinodermata. Characteristics include a star-shaped body and radially divergent axes of symmetry. The subphylum includes the class Asteroidea, the class Ophiuroidea, and the extinct order Somasteroidea.
The Ophiocistioidea is a class of extinct echinoderms from the Palaeozoic and early Mesozoic.
Eccentric sand dollar, also known as the sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a member of the order Clypeasteroida, better known as sand dollars, a species of flattened, burrowing sea urchins found in the northeast Pacific Ocean from Alaska to Baja California.
Comatulida is an order of crinoids. Members of this order are known as feather stars and mostly do not have a stalk as adults. The oral surface with the mouth is facing upwards and is surrounded by five, often divided rays with feathery pinnules. Comatulids live on the seabed and on reefs in tropical and temperate waters.
Ossicles are small calcareous elements embedded in the dermis of the body wall of echinoderms. They form part of the endoskeleton and provide rigidity and protection. They are found in different forms and arrangements in sea urchins, starfish, brittle stars, sea cucumbers, and crinoids. The ossicles and spines are the only parts of the animal likely to be fossilized after an echinoderm dies.
Diploporita is an extinct class of blastozoan that ranged from the Ordovician to the Devonian. These echinoderms are identified by a specialized respiratory structure, called diplopores. Diplopores are a double pore system that sit within a depression on a single thecal (body) plate; each plate can contain numerous diplopore pairs.
 | This prehistoric echinoderm-related article is a stub. You can help Wikipedia by expanding it. |