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Stylophora
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. Stylophorans have played a major role in debates over the origin of chordates, as under the calcichordate hypothesis they were interpreted as being stem-group chordates. However, multiple lines of evidence argue against the calcichordate hypothesis, and stylophorans are now widely agreed to belong to the echinoderm total group. Debate remains over whether they are stem-group echinoderms which predate the origin of radial symmetry, or highly modified descendants of radially symmetric echinoderms. Description The general stylophoran body plan consists of a flattened theca and a single jointed appendage which extends from it. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcichordate Hypothesis
The calcichordate hypothesis, formulated by British Museum paleontologist Richard Jefferies, holds that each separate lineage of chordate ( Cephalochordates, Urochordates, Craniates) evolved from its own lineage of mitrate, and thus the echinoderms and the chordates are sister groups, with the hemichordates as an out-group. It has been disproven by the discovery that the "tail" of Stylophorans contains a water vascular system, ambulacrum, and tube feet. However, the clade Olfactores was first proposed as part of the calcichordate theory, and has since been validated through genetic sequencing, albeit without the involvement of mitrates. Details The carpoids Cornuta and Mitrata are grouped together in a clade called Calcichordata. Cornutes and mitrates are viewed as sister groups, and mitrates represent stem group chordates. The mitrates (and thus the chordates) are all Dexiothetes, dexiothetism being a synapomorphy for the clade. Hypothetical phylogeny In the evolution o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcichordate Theory
The calcichordate hypothesis, formulated by British Museum paleontologist Richard Jefferies, holds that each separate lineage of chordate (Cephalochordates, Urochordates, Craniates) evolved from its own lineage of mitrate, and thus the echinoderms and the chordates are sister groups, with the hemichordates as an out-group. It has been disproven by the discovery that the "tail" of Stylophorans contains a water vascular system, ambulacrum, and tube feet. However, the clade Olfactores was first proposed as part of the calcichordate theory, and has since been validated through genetic sequencing, albeit without the involvement of mitrates. Details The carpoids Cornuta and Mitrate, Mitrata are grouped together in a clade called Calcichordata. Cornutes and mitrates are viewed as sister groups, and mitrates represent stem group chordates. The mitrates (and thus the chordates) are all dexiothetism, Dexiothetes, dexiothetism being a synapomorphy for the clade. Hypothetical phylogeny In t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echinoderm
An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial symmetry (pentamerous symmetry), and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone. The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian. Echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Echinodermata Orders
This List of echinoderm orders concerns the various classes and orders into which taxonomy (biology), taxonomists categorize the roughly 7000 extant species as well as the extinct species of the exclusively marine phylum Echinodermata. Subphylum Crinozoa Class Crinoidea * Subclass Articulata (Crinoidea), Articulata (540 species) ** Order Bourgueticrinida ** Order Comatulida ** Order Cyrtocrinida ** Order Hyocrinida ** Order Isocrinida ** Order Millericrinida * Subclass †Flexibilia * Subclass †Camerata (crinoid), Camerata * Subclass †Disparida Image:Comaster schlegelii.JPG, ''Comaster schlegelii'' (Comatulida) Image:Holopus 2.jpg, ''Holopus sp.'' (Cyrtocrinida) Image:Encrinus liliiformis 4.JPG, ''Encrinus liliiformis'' (Encrinida) Image:Calamocrinus diomedæ (Plate XXVIII) BHL4232451.jpg, ''Calamocrinus diomedae'' (Hyocrinida) Image:Proisocrinus ruberrimus.jpg, ''Proisocrinus ruberrimus'' (Isocrinida) Image:Liliocrinus polydactylus MHNT.jpg, ''Liliocrinus polydact ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cothurnocystis
''Cothurnocystis'' is a genus of small enigmatic echinoderms that lived during the Ordovician. Individual animals had a flat boot-shaped body and a thin rod-shaped appendage that may be a stem, or analogous to a foot or a tail. Fossils of ''Cothurnocystis'' species have been found in Nevada, Scotland, Czech Republic, France and Morocco. Taxonomy The position of the Stylophora, of which ''Cothurnocystis'' is a prominent representative, has been in a state of flux. Some scientists claim to be able to see a structurally very basic notochord in the tail, and consequently consider the Stylophora to be a group of primitive chordates, calling them the "Calcichordata". Alternatively these animals are considered related to echinoderms, as the shell (or test (biology), test) is similar in structure and composition to the tests of echinoderms. However, stylophorans are asymmetric organisms that lack either the radial symmetry typical of most echinoderms, or the bilateral symmetry of the ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cornuta
Cornuta is an extinct order of echinoderms. Along with the mitrates, they form the Stylophora 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 va .... Their first (probable) representative is '' Ponticulocarpus'' from the Spence Shale (mid Cambrian);, Ordovician examples also exist. References * External links * * Cornuta at fossilworks.org(retrieved 16 April 2016) Homalozoa Prehistoric animal orders Echinoderm orders {{paleo-echinoderm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mitrate
Mitrates are an extinct group of stem group echinoderms, which may be closely related to the hemichordates. Along with the cornutes, they form one half of the Stylophora. Morphology The organisms were a few millimetres long. Like the echinoderms, they are covered in armour plates, each of which comprises a single crystal of calcite. This is one of the features they share with the latter group, along with a water vascular system, only discovered in 2019. However, they do not display the familiar fivefold symmetry that more recent echinoderms possess, instead being close to (but not fully) bilaterally symmetrical. Their heads had two sides; one, flat, was covered with large "pavement-like" plates, the other, convex, bore smaller plates. Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar. At the opposite end was a hole which may have been mouth or anus - or both. They also bear features reminiscent of pharyngeal slit Pharyn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cornute
Cornuta is an extinct order of echinoderms. Along with the mitrate Mitrates are an extinct group of stem group echinoderms, which may be closely related to the hemichordates. Along with the cornutes, they form one half of the Stylophora. Morphology The organisms were a few millimetres long. Like the echinod ...s, they form the Stylophora. Their first (probable) representative is '' Ponticulocarpus'' from the Spence Shale (mid Cambrian);, Ordovician examples also exist. References * External links * * Cornuta at fossilworks.org(retrieved 16 April 2016) Homalozoa Prehistoric animal orders Echinoderm orders {{paleo-echinoderm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mitrate
Mitrates are an extinct group of stem group echinoderms, which may be closely related to the hemichordates. Along with the cornutes, they form one half of the Stylophora. Morphology The organisms were a few millimetres long. Like the echinoderms, they are covered in armour plates, each of which comprises a single crystal of calcite. This is one of the features they share with the latter group, along with a water vascular system, only discovered in 2019. However, they do not display the familiar fivefold symmetry that more recent echinoderms possess, instead being close to (but not fully) bilaterally symmetrical. Their heads had two sides; one, flat, was covered with large "pavement-like" plates, the other, convex, bore smaller plates. Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar. At the opposite end was a hole which may have been mouth or anus - or both. They also bear features reminiscent of pharyngeal slit Pharyn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemichordate
Hemichordata ( ) is a phylum which consists of triploblastic, eucoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta (acorn worms), and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, '' Planctosphaera pelagica''. The class Graptolithina, formerly considered extinct, is now placed within the pterobranchs, represented by a single living genus '' Rhabdopleura''. Acorn worms are solitary worm-shaped organisms. They generally live in burrows (the earliest secreted tubes) and are deposit feeders, but some species are pharyngeal filter feeders, while the family are free living detritivores. Many are well known for their production and accumulation of various halogenated phenols and pyrroles. Pterobranchs are filter-feeders, mostly colonial, living in a collagenous ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deuterostomes
Deuterostomes (from Greek: ) are bilaterian animals of the superphylum Deuterostomia (), typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia comprises three phyla: Chordata, Echinodermata, Hemichordata, and the extinct clade Cambroernida. In deuterostomes, the developing embryo's first opening (the blastopore) becomes the anus and cloaca, while the mouth is formed at a different site later on. This was initially the group's distinguishing characteristic, but deuterostomy has since been discovered among protostomes as well. The deuterostomes are also known as enterocoelomates, because their coelom develops through pouching of the gut, enterocoely. Deuterostomia's sister clade is Protostomia, animals that develop mouth first and whose digestive tract development is more varied. Protostomia includes the ecdysozoans and spiralians, as well as the extinct ''Kimberella''. Together with the Xenacoelomorpha, these constitute t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Simon Conway Morris
Simon Conway Morris (born 1951) is an English palaeontologist, evolutionary biologist, and astrobiologist known for his study of the fossils of the Burgess Shale and the Cambrian explosion. The results of these discoveries were celebrated in Stephen Jay Gould's 1989 book '' Wonderful Life''. Conway Morris's own book on the subject, ''The Crucible of Creation'' (1998), however, is critical of Gould's presentation and interpretation. Conway Morris, a Christian, holds to theistic views of biological evolution. He has held the Chair of Evolutionary Palaeobiology in the Department of Earth Sciences, University of Cambridge since 1995. Biography Early years Conway Morris was born on 6 November 1951. A native of Carshalton, Surrey, he was brought up in London, England. and went on to study geology at Bristol University, achieving a First Class Honours degree. He then moved to Cambridge University and completed a PhD at St John's College under Harry Blackmore Whittington. He ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
