31-643: See text. Conulariida are an extinct group of medusozoan cnidarians known from fossils spanning from the latest Ediacaran up until the Late Triassic . They are almost exclusively known from their hard external structures (alternatively referred to as a theca, periderm or test), which were pyramidal in shape and made up of numerous lamellae. The conulariids are fossils preserved as shell-like structures made up of rows of calcium phosphate rods, resembling an ice-cream cone with fourfold symmetry, usually four prominently-grooved corners. New rods were added as
62-482: A medusa stage in their life cycle. The basic pattern is medusa (usually the adult or sexual phase), planula larva , polyp , medusa. Symmetry is tetramerous, with parts in fours or multiples of four. The mitochondrial DNA molecules are linear rather than circular as in anthozoans and almost all other animals. The cnidae, the explosive cells characteristic of the Cnidaria and used in prey capture and defence, are of
93-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
124-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
155-643: A cnidarian because of its possession of nematocysts, but molecular studies using 18S rDNA sequences have placed it closer to Myxozoa . Further studies involving 28S rDNA sequences suggest that it is either part of the hydrozoan clade Leptothecata , or a sister taxon to Hydrozoa, and does not group with myxozoans. Ctenophora [REDACTED] Anthozoa [REDACTED] [REDACTED] Staurozoa [REDACTED] Hydrozoa [REDACTED] Polypodiozoa ? [REDACTED] Cubozoa [REDACTED] Scyphozoa [REDACTED] Bilateria [REDACTED] Medusozoans differ from anthozoans in having
186-537: A conulariid at all, and the definite late Ediacaran conulariid Paraconularia ediacara , the Conulata fossil record begins with undeniable specimens in the Upper Ediacaran and extends without significant break through numerous major mass extinctions. The Conulariids finally disappear from the fossil record during the Late Triassic , by which time they were very rare, with only 8 documented occurrences across
217-417: A medusa which separates and swims away. Staurozoa is a small group commonly known as stalked jellyfish. The animals remain attached to the substrate by a stalk at the opposite end from the mouth. Staurozoans can be regarded as large polyps that have partially differentiated into sexually mature medusae. These spawn gametes which develop into non-swimming planulae that crawl away to new locations. Hydrozoa
248-401: A process known as strobilation . Cubozoa is a group commonly known as box jellyfish, that occur in tropical and warm temperate seas. They have cube-shaped, transparent medusae and are heavily-armed with venomous nematocysts. Cubozoans have planula larvae, which settle and develop into sessile polyps, which subsequently metamorphose into sexual medusae, the oral end of each polyp changing into
279-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
310-662: A single type, there being nematocysts but no spirocysts or ptychocysts. In contrast, the anthozoan life cycle involves a planula larva which settles and becomes a sessile polyp, which is the adult or sexual phase. There is considerable divergence from the basic life cycle pattern among medusozoans. Scyphozoa is the group commonly known as "true jellyfish" and occur in tropical, temperate and polar seas worldwide. Scyphozoans generally have planula larvae that develop into sessile polyps. These reproduce asexually, producing similar polyps by budding, and then either transform into medusae, or repeatedly bud medusae from their upper surface in
341-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
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#1732800810664372-526: Is a clade in the phylum Cnidaria , and is often considered a subphylum. It includes the classes Hydrozoa , Scyphozoa , Staurozoa and Cubozoa , and possibly the parasitic Polypodiozoa . Medusozoans are distinguished by having a medusa stage in their often complex life cycle, a medusa typically being an umbrella-shaped body with stinging tentacles around the edge. With the exception of some Hydrozoa (and Polypodiozoa), all are called jellyfish in their free-swimming medusa phase. The phylum Cnidaria
403-433: Is a large group of solitary and colonial cnidarians from both marine and freshwater environments worldwide. Hydrozoans exhibit the greatest variety of life cycles among medusozoans, with either the polyp or the medusa stage being missing in some groups. In general, medusae are budded laterally from polyps, become mature and spawn, releasing gametes into the water. The planulae may settle to become polyps or continue living in
434-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
465-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
496-524: Is now also thought that the conulate trilobozoans derived their fourfold symmetry from a sixfold symmetry, as seen in Vendoconularia . This in turn, is thought to be originally derived from an ancestral disk-like trilobozoan three-fold symmetry. Conulariids have generally been thought to be of Cnidarian affinity, occupying a position near the base of the Cnidarian family tree. However, since
527-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
558-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
589-445: Is widely accepted as being monophyletic and consisting of two clades, Anthozoa and Medusozoa. Anthozoa includes the classes Hexacorallia , the hard corals, and Octocorallia , the soft corals, as well as Ceriantharia , the tube-dwelling anemones. There is strong support for this group having been the first to branch off from the ancestral line. Medusozoa includes the classes Staurozoa , Cubozoa , Scyphozoa and Hydrozoa , but
620-650: The Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
651-584: The 2010s, authors consider conulariids to be members of the subclade Medusozoa , though their exact placement within the clade is uncertain. Conulariids produced pearls within their shells, similar to the way molluscs such as oysters, other pelecypods , and some gastropods do today. These pearls give a clue as to the internal anatomy of the conulariid animal. But due to their calcium phosphate composition, their crystal structure, and their extreme age, these pearls tend to be rather unattractive for use in or as decorative objects. Medusozoa Medusozoa
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#1732800810664682-440: The earliest known animal predator from the late Ediacaran . Burgessomedusa from the mid- Cambrian Burgess Shale is the oldest known free-living medusa (commonly known as jellyfish). The affinities of the class Polypodiozoa , containing the single species Polypodium hydriforme , have long been unclear. This species is an endoparasite of fish eggs and has a peculiar life cycle. It has traditionally been considered to be
713-754: The entire Triassic. Their extinction may have been due to the rise of durophagous organisms as part of the Mesozoic marine revolution . In North America, conulariids are generally more common in rocks of Ordovician and Carboniferous age. Conulariids were benthic animals that were sessile and attached to a substrate at the base of the theca, older individuals may have become recumbent (tipped over). They are generally proposed to have been predators, using tentacles to ensnare prey. About 20 genera and 150 species are known, but except for local occurrences, Conulariids are relatively uncommon. The conulariids were originally thought to be anthozoan cnidarians. However,
744-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
775-540: The lack of septa or other features diagnostic of anthozoans led researchers to abandon this hypothesis. Ivantsov and Fedonkin (2002) posit that the conulariids were ancestrally tri-radially symmetrical, as typified with Vendoconularia , typical of the structure seen in Vendozooans . Conulariids are, however, technically a part of the Ediacaran biota as their fossil record starts at latest parts of that period. It
806-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
837-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
868-442: The organism grew in length; the rod-based growth falsely gives the fossils a segmented appearance. Exceptional soft-part preservation has revealed that soft tentacles protruded from the wider end of the cone, and a holdfast from the pointed end attached the organisms to hard substrate. The prevailing reconstruction of the organism has it look superficially like a sea anemone sitting inside an angular, hard cone held perpendicular to
899-548: The relationships between these are unclear. Analysis using ribosomal RNA subunits suggests that within Medusozoa, Staurozoa was the first group to diverge, with Cubozoa and Scyphozoa forming a clade, a sister group to Hydrozoa. Further study involving the order of mitochondrial genes supports this view, and their possession of linear mitochondrial genomes is striking evidence of the monophyly of medusozoans. The stem group of Medusozoa also includes Auroralumina attenboroughii ,
930-400: The substrate. Conulariid shell is composed of francolite with carbonate ion concentration 8.1 wt%. The lattice parameters of conulariid apatite are a = 9.315(7) Å, c = 6.888(3) Å. The fine structure of their shell comprises multiple lamellae of alternately organic-rich and organic-poor layers. With the inclusion of the possible Ediacaran conulariid Vendoconularia , which may or may not be
961-413: The water column as medusae. Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes