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Homalozoa
Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms, prehistoric marine invertebrates. They are also referred to as carpoids. Description The Homalozoa lacked the typical pentamer body form of other echinoderms, but all were sessile animals. Instead all Homalozoans were markedly asymmetric, and were extremely variable in forms. The body (theca) was covered with calcite plates with a number of openings. Their form is in some cases so unusual that it is unclear which openings are to be considered as mouth and anus. Many of them were stalked, similar to sea lilies (crinoids), but often their bodies were bent over, so that the mouth and anus projected forwards rather than upwards. Some forms, especially stylophorans, rested flat on the sea floor. In some forms the single ray ( brachiole or aulacophore) possessed an ambulacral groove. It has been claimed that some forms possessed gills and gill slits. Taxonomy Homalozoans were traditionally considered to be ... [...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] |
Ctenocystoidea
Ctenocystoidea is an extinct clade of echinoderms, which lived during the Cambrian and Ordovician periods. Unlike other echinoderms, ctenocystoids had bilateral symmetry, or were only very slightly asymmetrical. They are believed to be one of the earliest-diverging branches of echinoderms, with their bilateral symmetry a trait shared with other deuterostomes. Ctenocystoids were once classified in the taxon Homalozoa, also known as Carpoidea, alongside cinctans, solutes, and stylophorans. Homalozoa is now recognized as a polyphyletic group of echinoderms without radial symmetry. Ctenocystoids were geographically widespread during the Middle Cambrian, with one species surviving into the Late Ordovician. Description Like other echinoderms, ctenocystoids had a skeleton made of stereom plates. Ctenocystoids had near bilateral symmetry, with some species exhibiting slightly asymmetric plate shapes. Like cinctans and '' Ctenoimbricata'', most ctenocystoids had large marginal plates ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crinozoa
Crinozoa is a subphylum of mostly sessile echinoderms, of which the crinoids, or sea lilies and feather stars, are the only extant members. Crinozoans have an extremely extensive fossil history. Classes within Crinozoa As published in the ''Treatise on Invertebrate Paleontology'', Crinozoa included all stemmed groups except for the few stemmed basal solutes. When Blastozoa was erected to contain stalked forms with brachioles rather than arms, only Crinoidea and Paracrinoidea remained within Crinozoa. Recent cladistic work has placed Paracrinoidea under Blastozoa, although some sources continue to include Paracrinoidea. One proposal for the cladistic placement of the Homalozoan classes groups Stylophora together with crinoids to form Crinozoa. A 2024 survey of recent research finds more support for Homalozoa as a paraphyletic assemblage along the echinoderm stem group, but noted that the position of Stylophora in particular was uncertain. If neither Paracrinoidea nor Stylo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solute (echinoderm)
Soluta is an extinct class of echinoderms that lived from the Middle Cambrian to the Early Devonian. The class is also known by its junior synonym Homoiostelea. Soluta is one of the four "carpoid" classes, alongside Ctenocystoidea, Cincta, and Stylophora, which made up the obsolete subphylum Homalozoa. Solutes (or solutans) were asymmetric animals with a stereom skeleton and two appendages, an arm extending anteriorly and a posterior appendage called a homoiostele. Biology Most solutes were free-living, but the basal solutan ''Coleicarpus'' used its homoiostele as a holdfast, as did juvenile ''Castericystis''. Classification The phylogenetic position of Soluta is contentious. Solutans are widely agreed to be echinoderms, though the outmoded calcichordate hypothesis held that they were ancestral to both echinoderms and chordates. Within echinoderms, one hypothesis holds that solutes are stem-group echinoderms which branched off before echinoderms evolved radial symmetry. An ... [...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] |
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] |
Cincta
Cincta is an extinct class of echinoderms that lived only in the Middle Cambrian epoch. Homostelea is a junior synonym. The classification of cinctans is controversial, but they are probably part of the echinoderm stem group. Cinctans were sessile, asymmetrical animals with a skeleton made of stereom plates and a racquet-shaped body composed of a theca and stele. They may have had a lifestyle similar to modern tunicates, filter-feeding by pumping water through gill slits in their pharynx. Description Cinctans were asymmetrical animals, though some species were nearly bilaterally symmetrical. Like all echinoderms, cinctans have a skeleton made of plates of stereom. The body of cinctans was divided into two sections, the main body, called the theca, and a posterior appendage called a stele. The overall shape of cinctans has been compared to a tennis racquet. The theca of cinctans was surrounded on its margins by a frame of large stereom plates called a cinctus, and the dorsal and ... [...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] |
Marine Invertebrate
Marine invertebrates are invertebrate animals that live in marine habitats, and make up most of the macroscopic life in the oceans. It is a polyphyletic blanket term that contains all marine animals except the marine vertebrates, including the non-vertebrate members of the phylum Chordata such as lancelets, sea squirts and salps. As the name suggests, marine invertebrates lack any mineralized tissue, mineralized axial skeleton, axial endoskeleton, i.e. the vertebral column, and some have evolved a rigid seashell, shell, test (biology), test or exoskeleton for protection and/or aquatic locomotion, locomotion, while others rely on hydroskeleton, internal fluid pressure to support their bodies. Marine invertebrates have a large variety of body plans, and have been categorized into over 30 phyla. Evolution The earliest animals were marine invertebrates, that is, vertebrates came later. Animals are multicellular eukaryotes, and are distinguished from plants, algae, and fungi by l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
