|
Crinoidea
Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which 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. They live in both shallow water and in depths as great as . 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crinoid Anatomy
Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which 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. They live in both shallow water and in depths as great as . 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comatulida
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. Taxonomy Bourgueticrinida, the sea lilies, has traditionally been viewed as an order of Articulata and a sister taxon to Comatulida. A study published in 2011 suggested that it should be renamed Bourgueticrinina and viewed as a suborder of Comatulida. Characteristics Like other echinoderms, comatulids have pentamerous symmetry (five sided) as adults though the larvae have bilateral symmetry. Late in their development, the larvae are attached to the seabed by a stalk, but this is broken at metamorphosis and the juvenile crinoid is free living. The body has an endoskeleton made from a number of articulated calcareous plates known as ossicles covered by a thin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pentacrinoidea
Pentacrinoidea is a subclass of crinoids containing all members of Crinoidea except for the exclusively Paleozoic camerates (subclass Camerata). It was originally named in 1918 by Otto Jaekel, who hypothesized a fundamental split between camerate and non-camerate crinoids. Later workers doubted this interpretation, and Pentacrinoidea was rarely used during the rest of the 20th century. Recent phylogenetic work has provided strong support for Jaekel's hypothesis, and Pentacrinoidea was reinstated in a 2017 revision of crinoid systematics. Pentacrinoidea includes most major crinoid groups, such as the living Articulata and extinct Flexibilia (together forming the parvclass Cladida) as well as the extinct Disparida. It is a stem-based taxon, defined as including all crinoids closer to '' Pentacrinites'' (a Jurassic articulate) or '' Apektocrinus'' (an Early Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echinoderm
An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) 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 entirely marine phylum. The first definitive echinoderms appeared near the start of the Cambrian. The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs, and limbs; in some cases, they can undergo complete regeneration from a single li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Camerata (Crinoidea)
The Camerata or camerate crinoids are an extinct subclass of Paleozoic stalked crinoids. They were some of the earliest crinoids to originate during the Early Ordovician, reached their maximum diversity during the Mississippian, and became extinct during the Permian–Triassic extinction event. Camerates are the sister group of Pentacrinoidea, which contains all other crinoids (including living species). The two largest camerate subgroups are the orders Diplobathrida and Monobathrida. Anatomically, they are distinguished by:Treatise on Invertebrate Paleontology, Volume T. Echinodermata: Crinoidea. Ubaghs et al. Editors: R. C. Moore and C. Teichert. 1978. *fused junctions between the plates of the cup *brachial plates incorporated into the cup *tegmen forming a rigid roof over the mouth *no less than ten and sometimes a very large number of free arms, often pinnulate Subdivisions * Order Cladida? * '' Adelphicrinus'' * '' Eknomocrinus'' * '' Cnemecrinus'' * '' Quechuacrinus' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Articulata (Crinoidea)
Articulata are a subclass or superorder within the class Crinoidea, including the only living crinoid species. They are commonly known as sea lilies (stalked crinoids) or feather stars (unstalked crinoids). 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. Articulata first appeared in the fossil record during the Triassic period although other, now extinct crinoid groups, originated in the Ordovician. Characteristics Articulata exhibit pentamerous symmetry. The stalk, which consists of numerous disks held together by ligaments, supports a calyx or cup made of circlets of calcerous plates. In Comatulids, the stalk develops following the larval stage, but the juveniles shed all but the topmost disk to take up a free-living existence. Five often branched arms, which consist of articulated series of Ossicle (echinoderm), ossicles, extend from the oral plate and form the food-capture ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flexibilia
Flexibilia is a superorder of specialized Paleozoic (Middle Ordovician to Permian) crinoids. They exhibited a conserved body plan and consistent suite of characteristics throughout their long history. Previously considered a subclass with unclear affinities, later investigation determined that flexibles are well-nested within Cladida, a broad group ancestral to living articulate crinoids. The Ordovician cladid '' Cupulocrinus'' acts as an intermediate form linking the generalized anatomy of other early cladids with the distinctive anatomy of flexibles, and several studies have considered it to be ancestral to the rest of the group. Although flexibles never reached the same abundance or diversity as many other crinoid groups, they remained a reliable component of crinoid faunas, particularly from the Silurian onwards. Flexible fossils are very rare in the Ordovician (the most common taxa being ''Cupulocrinus'' and '' Protaxocrinus''), but the Late Ordovician appears to have been a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disparida
Disparida is an parvclass of extinct marine animals in the class Crinoidea. Disparids are a speciose and morphologically diverse group of crinoids distinguished by their monocyclic calyx and slender arms without pinnules. They range from the Early Ordovician (Tremadocian) to Middle Permian, reaching their highest diversity during the Late Ordovician. While many disparids had a generalized shape typical of other stalked crinoids, some subgroups achieved strange forms. The long-lasting Calceocrinidae were recumbent forms, with a flattened crown bent back onto a stalk which rested on the seafloor. Other unusual disparid families include the armless Zophocrinidae, the spiral-armed Myelodactylidae, and the diminutive, simplified Pisocrinidae. Disparids have long been classified by the structure of their radial plates and different planes of symmetry, but a cumulative phylogenetic approach has failed to confirm the validity of many proposed subgroups. Nevertheless, Disparida itsel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Starfish
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 live 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 below the surface. Starfish are marine invertebrates. They typically have a central disc and usually five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surfa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Urchin
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 . The spherical, hard shells (tests) of sea urchins are round and spiny, ranging in diameter from . 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. Predators that eat sea urchins include a wide variety of fish, starfish, crabs, marine mammals. Sea urchins are also used as food especially in Japan. Adult sea urchins have fivefold symmetry, but their pluteus larvae feature bilateral (mirror) symmetry, indicating that the sea urchin belongs to the Bilateria group of animal phyla, which also comprises the chordates and the arthropods, the annelids and the molluscs, and are found in every ocean and in every climate, from the tropics to the po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Cucumber
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. Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcified structures that are usually reduced to isolated microscopic ossicles (or sclerietes) joined by connective tissue. In some species these can som ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Era (geology)
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (scientific branch of geology that aims to determine the age of rocks). It is used primarily by Earth scientists (including geologists, paleontologists, geophysicists, geochemists, and paleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardized international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely defi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
