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Eumetazoan
Eumetazoa (), also known as diploblasts, Epitheliozoa, or Histozoa, are a proposed basal animal clade as a sister group of the Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa. Several other extinct or obscure life forms, such as ''Iotuba'' and ''Thectardis'', appear to have emerged in the group. Characteristics of eumetazoans include true tissues organized into germ layers, the presence of neurons and muscles, and an embryo that goes through a gastrula stage. Some phylogenists once speculated the sponges and eumetazoans evolved separately from different single-celled organisms, which would have meant that the animal kingdom does not form a clade (a complete grouping of all organisms descended from a common ancestor). However, genetic studies and some morphological characteristics, like the common presence of choanocytes, now unanimously support a common origin. Traditionally, e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Placozoa
The Placozoa are a basal form of marine free-living (non-parasitic) multicellular organism. They are the simplest in structure of all animals. Three genera have been found: the classical ''Trichoplax adhaerens'', ''Hoilungia hongkongensis'', and ''Polyplacotoma mediterranea'', where the last appears most basal. The last two have been found only since 2017. Although the Placozoa were first discovered in 1883 by the German zoologist Franz Eilhard Schulze (1840–1921) and since the 1970s more systematically analyzed by the German protozoologist Karl Gottlieb Grell (1912–1994), a common name does not yet exist for the taxon; the scientific name means "flat animals". Biology ''Trichoplax'' is a small, flattened, animal around across. An amorphous multi-celled body, analogous to a single-celled ''Amoeba'', it has no regular outline, although the lower surface is somewhat concave, and the upper surface is always flattened. The body consists of an outer layer of simple epithelium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chancelloriida
The Chancelloriids are an extinct family of superficially sponge-like animals common in sediments from the Early Cambrian to the early Late Cambrian. Many of these fossils consists only of spines and other fragments, and it is not certain that they belong to the same type of organism. Other specimens appear to be more complete and to represent sessile, radially symmetrical hollow bag-like organisms with a soft skin armored with star-shaped calcareous sclerites from which radiate sharp spines. Classifying the chancelloriids is difficult. Some paleontologists classify them as sponges, an idea which chancelloriids' sessile lifestyle and simple structure make plausible. Other proposals suggest that they were more advanced, or at least originated from more advanced ancestors; for example chancelloriids' skins appear to be much more complex than those of any sponge. It has been suggested that chancelloriids were related to the "chain mail" armored slug-like halkieriids, which are typic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ediacaran
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia. The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years. Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at . The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nephrozoa
Nephrozoa is a major clade of bilaterians, divided into the protostomes and the deuterostomes, containing almost all animal phyla and over a million extant species. Its sister clade is the Xenacoelomorpha. The Ambulacraria (conventionally deuterostomes) was formerly thought to be sister to the Xenacoelomorpha, forming the Xenambulacraria as basal Deuterostomes, or basal Bilateria invalidating Nephrozoa and Deuterostomes in earlier studies. The coelom, the digestive tract and excretory organs (nephridia), and nerve cords developed in the Nephrozoa. It has been argued that, because protonephridia are only found in protostomes, they cannot be considered a synapomorphy of this group. This would make Nephrozoa an improper name, leaving Eubilateria as this clade's name. Chordates (which include all the vertebrates) are deuterostomes. It seems very likely that the ''Kimberella ''Kimberella'' is an extinct genus of bilaterian known only from rocks of the Ediacaran period. The s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Onychophora
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus''), is a phylum of elongate, soft-bodied, many-legged panarthropods. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. They prey upon other invertebrates, which they catch by ejecting an adhesive slime. Approximately 200 species of velvet worms have been described, although the true number of species is likely greater. The two extant families of velvet worms are Peripatidae and Peripatopsidae. They show a peculiar distribution, with the peripatids being predominantly equatorial and tropical, while the peripatopsids are all found south of the equator. It is the only phylum within Animalia that is wholly endemic to terrestrial environments, at least among extant members. Velvet worms are generally c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nematomorpha
Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair worms, hairsnakes, or Gordian worms) are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. Most species range in size from long, reaching 2 metres in extreme cases, and in diameter. Horsehair worms can be discovered in damp areas, such as watering troughs, swimming pools, streams, puddles, and cisterns. The adult worms are free-living, but the larvae are parasitic on arthropods, such as beetles, cockroaches, mantises, orthopterans, and crustaceans. About 351 freshwater species are known and a conservative estimate suggests that there may be about 2000 freshwater species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorphs often coil themselves in tight balls that resemble knots. Description and biology Nematomorphs possess an external cuticle without cilia. Internally, they have only longitudin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nematoda
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broad range of environments. Less formally, they are categorized as Helminths, but are taxonomically classified along with arthropods, tardigrades and other moulting animals in the clade Ecdysozoa, and unlike flatworms, have tubular digestive systems with openings at both ends. Like tardigrades, they have a reduced number of Hox genes, but their sister phylum Nematomorpha has kept the ancestral protostome Hox genotype, which shows that the reduction has occurred within the nematode phylum. Nematode species can be difficult to distinguish from one another. Consequently, estimates of the number of nematode species described to date vary by author and may change rapidly over time. A 2013 survey of animal biodiversity published in the mega jou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Priapulida
Priapulida (priapulid worms, from Gr. πριάπος, ''priāpos'' 'Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility, because their general shape and their extensible spiny introvert (eversible) proboscis may resemble the shape of a human penis. They live in the mud and in comparatively shallow waters up to deep. Some species show a remarkable tolerance for hydrogen sulfide and anoxia. They can be quite abundant in some areas. In an Alaskan bay as many as 85 adult individuals of ''Priapulus caudatus'' per square meter has been recorded, while the density of its larvae can be as high as 58,000 per square meter. Together with Echiura and Sipuncula, they were once placed in the taxon Gephyrea, but consistent morphological and molecular evidence supports their belonging to Ecdysozoa, which also includes arthropods and nematodes. Fossil findings show that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loricifera
Loricifera (from Latin, '' lorica'', corselet (armour) + ''ferre'', to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals that had been determined to be 37 described species, in 9 genera, but in 2021 has increased to 43 species. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their sizes range from 100 μm to ca. 1 mm. They are characterised by a protective outer case called a lorica and their habitat is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in 1983 by R.M. Kristensen, near Roscoff, France. They are among the most recently discovered groups of animals. They attach themselves quite firmly to the substrate, and hence remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinorhyncha
Kinorhyncha ( grc, κινέω, kīnéō, I move, ' "snout") is a phylum of small marine invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons. Modern species are or less, but Cambrian forms could reach . Anatomy Kinorhynchs are limbless animals, with a body consisting of a head, neck, and a trunk of eleven segments. They are the only members of Ecdysozoa, except from the panarthropoda, with a segmented body. Juveniles have eight or nine segments, depending on genus, with the last two or three being added later during growth. Like other ecdysozoans they do not have external cilia, but instead have a number of spines along the body, plus up to seven circles of spines around the head. These spines are used for locomotion, withdrawing the head and pushing forward, then gripping the substrate with the spines while drawing up the body. The body wall consists of a thin syncitial layer, which secretes a tough ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ecdysozoa
Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo ''et al.'' in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes. A large study in 2008 by Dunn ''et al.'' strongly supported the Ecdysozoa as a clade, that is, a group consisting of a common ancestor and all its descendants. The group is also supported by morphological characters, and includes all animals that grow by ecdysis, moulting their cuticle. The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques, while others contested the interpretation of the molecular data. Etymology The name ''Ecdysozoa'' stems etymologically . Characteristics The most notable characteristic shared by ecdysozoans is a three-layered cuticle (four in Tardigrada) composed of orga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protostomia
Protostomia () is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister clade, Deuterostomia. Well known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them. Together with the Deuterostomia and Xenacoelomorpha, these form the clade Bilateria, animals with bilateral symmetry, anteroposterior axis and three germ layers. Protostomy In animals at least as complex as earthworms, the first phase in gut development involves the embryo forming a dent on one side (the blastopore) which deepens to become its digestive tube (the archenteron). In the sister-clade, the deuterostomes (), the original dent becomes the anus while the gut event ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
