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Due to the usually poor preservation, detailed reconstructions of the head region are only available for a handful of lobopodian species. The head of a lobopodian is more or less bulbous, and sometime possesses a pair of pre-ocular, presumely protocerebral appendages – for example, primary antennae or well-developed fr... | Lobopodia | Wikipedia | 462 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
The lobopods are flexible and loosely conical in shape, tapering from the body to tips that may or may not bear claws. The claws, if present, are hardened structures with a shape resembling a hook or gently-curved spine. Claw-bearing lobopods usually have two claws, but single claws are known (e.g. posterior lobopods... | Lobopodia | Wikipedia | 333 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
The gut of lobopodians is often straight, undifferentiated, and sometimes preserved in the fossil record in three dimensions. In some specimens the gut is found to be filled with sediment. The gut consists of a central tube occupying the full length of the lobopodian's trunk, which does not change much in width - at le... | Lobopodia | Wikipedia | 492 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Based on external morphology, lobopdians may fall under different categories — for example the general worm-like taxa as "xenusiid" or "xenusian"; xenusiid with sclerite as "armoured lobopodians"; and taxa with both robust frontal appendages and lateral flaps as "gilled lobopodians". Some of them were originally define... | Lobopodia | Wikipedia | 307 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Dinocaridids with lobopodian affinities (due to shared features like annulation and lobopods) are referred to as "gilled lobopodians" or "gilled lobopods". These forms sport a pair of flaps on each trunk segment, but otherwise no signs of arthropodization, in contrast to more derived dinocaridids like the Radiodonta th... | Lobopodia | Wikipedia | 455 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Lobopodians possibly occupied a wide range of ecological niches. Although most of them had undifferentiated appendages and straight gut, which would suggest a simple sediment-feeding lifestyle, sophisticated digestive glands and large size of gilled lobopodians and siberiids would allow them to consume larger food item... | Lobopodia | Wikipedia | 409 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Based on their apparently onychophoran-like morphology (e.g. annulated cuticle, lobopodous appendage with claws), lobopodians were originally thought to be present a group of paleozoic onychophorans. This interpretation was challenged after the discovery of lobopodians with arthropod and tardigrade-like characteristics... | Lobopodia | Wikipedia | 299 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Compared to other panarthropod stem-groups, suggestion on the lobopodian members of arthropod stem-group is relatively consistent — siberiid like Megadictyon and Jianshanopodia occupied the basalmost position, gilled lobopodians Pambdelurion and Kerygmachela branch next, and finally lead to a clade compose of Opabinia... | Lobopodia | Wikipedia | 308 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Diania, a genus of armoured lobopodian with stout and spiny legs, were originally thought to be associated within the arthropod stem-group based on its apparently arthropod-like (arthropodized) trunk appendages. However, this interpretation is questionable as the data provided by the original description are not consis... | Lobopodia | Wikipedia | 401 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
Lobopodian taxa of the tardigrade stem-group is unclear. Aysheaia or Onychodictyon ferox had been suggest to be a possible member, based on the high claw number (in Aysheaia) and/or terminal lobopods with anterior-facing claws (in both taxa). Although not widely accepted, there are even suggestions that Tardigrada its... | Lobopodia | Wikipedia | 497 | 43184 | https://en.wikipedia.org/wiki/Lobopodia | Biology and health sciences | Ecdysozoa | Animals |
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 , reaching in extreme cases, and in diameter. Horsehair worms can be ... | Nematomorpha | Wikipedia | 413 | 43196 | https://en.wikipedia.org/wiki/Nematomorpha | Biology and health sciences | Ecdysozoa | Animals |
In Spinochordodes tellinii and Paragordius tricuspidatus, which have grasshoppers and crickets as their hosts, the infection acts on the infected host's brain. This causes the host insect to seek water and drown itself, thus returning the nematomorph to water. P. tricuspidatus is also remarkably able to survive the pre... | Nematomorpha | Wikipedia | 415 | 43196 | https://en.wikipedia.org/wiki/Nematomorpha | Biology and health sciences | Ecdysozoa | Animals |
The phylum is placed along with the Ecdysozoa clade of moulting organisms that include the Arthropoda. Their closest relatives are the nematodes. The two phyla make up the group Nematoida in the clade Cycloneuralia. During the larval stage, the animals show a resemblance to adult kinorhyncha and some species of Loricif... | Nematomorpha | Wikipedia | 370 | 43196 | https://en.wikipedia.org/wiki/Nematomorpha | Biology and health sciences | Ecdysozoa | Animals |
Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for 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 animals. In appearance they have variously be... | Onychophora | Wikipedia | 342 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Anatomy and physiology
Velvet worms are segmented animals with a flattened cylindrical body cross-section and rows of unstructured body appendages known as oncopods or lobopods (informally: stub feet). They reach lengths between depending on species, with the smallest known being Ooperipatellus nanus and the largest k... | Onychophora | Wikipedia | 459 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Crural glands are situated at the shoulder of the legs, extending into the body cavity. They open outwards at the crural papillae—small wart-like bumps on the belly side of the leg—and secrete chemical messenger materials called pheromones. Their name comes from the Latin cruralis meaning "of the legs".
Coxal vesicles ... | Onychophora | Wikipedia | 321 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
On the first head segment is a pair of slender antennae, which serve in sensory perception. They probably do not correspond directly to the antennae of the Arthropoda, but perhaps rather with their "lips" or labrum. At their base is a pair of simple eyes, except in a few blind species. In front of these, in many Austra... | Onychophora | Wikipedia | 439 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
On the third head segment, to the left and right of the mouth, are two openings called "oral papillae", with each containing a large, heavily branched slime gland. These slime glands lie roughly in the center of a velvet worm's body and secrete a sort of milky-white slime. The slime is used to both ensnare prey and act... | Onychophora | Wikipedia | 170 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Unlike the arthropods, velvet worms do not possess a rigid exoskeleton. Instead, their fluid-filled body cavity acts as a hydrostatic skeleton, similarly to many distantly related soft-bodied animals that are cylindrically shaped, for example sea anemones and various worms. Pressure of their incompressible internal bod... | Onychophora | Wikipedia | 511 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The solubility of these pigments is a useful diagnostic character: in all arthropods and tardigrades, the body pigment is soluble in ethanol. This is also true for the Peripatidae, but in the case of the Peripatopsidae, the body pigment is insoluble in ethanol | Onychophora | Wikipedia | 67 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Within the connective tissue lie three continuous layers of unspecialised smooth muscular tissue. The relatively thick outer layer is composed of annular muscles, and the similarly voluminous inner layer of longitudinal muscles. Between them lie thin diagonal muscles that wind backward and forward along the body axis i... | Onychophora | Wikipedia | 392 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The haemocoel is divided by a horizontal partition, the diaphragm, into two parts: The pericardial sinus along the back and the perivisceral sinus along the belly. The former encloses the tube-like heart, and the latter, the other organs. The diaphragm is perforated in many places, enabling the exchange of fluids betwe... | Onychophora | Wikipedia | 503 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Unlike the arthropods, the velvet worms are unable to control the openings of their tracheae; the tracheae are always open, entailing considerable water loss in arid conditions. Water is lost twice as fast as in earthworms and forty times faster than in caterpillars. For this reason, velvet worms are dependent upon hab... | Onychophora | Wikipedia | 412 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
In almost every segment is a pair of excretory organs called nephridia, which are derived from coelom tissue. Each consists of a small pouch that is connected, via a flagellated conductor called a nephridioduct, to an opening at the base of the nearest leg known as a nephridiopore. The pouch is occupied by special cell... | Onychophora | Wikipedia | 499 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The rhabdomeric eyes of the Onychophora are thought to be homologous with the median ocelli of arthropods; this would suggest that the last common ancestor of arthropods may have only had median ocelli.
However, the innervation shows that the homology is limited: The eyes of Onychophora form behind the antenna, whereas... | Onychophora | Wikipedia | 457 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
There are different mating procedures: In some species males deposit their spermatophore directly into the female's genitals opening, while others deposit it on the female's body, where the cuticle will collapse, allowing the sperm cells to migrate into the female. There are also Australian species where the male place... | Onychophora | Wikipedia | 492 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Velvet worms are photophobic: They are repelled by bright light sources. Because the danger of desiccation is greatest during the day and in dry weather, it is not surprising that velvet worms are usually most active at night and during rainy weather. Under cold or dry conditions, they actively seek out crevices in whi... | Onychophora | Wikipedia | 281 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The slime glands themselves are deep inside the body cavity, each at the end of a tube more than half the length of the body. The tube both conducts the fluid and stores it until it is required. The distance that the animal can propel the slime varies; usually it squirts it about a centimetre, but the maximal range has... | Onychophora | Wikipedia | 436 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Velvet worms/Onychophora move in a slow and gradual motion that makes them difficult for prey to notice. Their trunk is raised relatively high above the ground, and they walk with non-overlapping steps.
To move from place to place, the velvet worm crawls forward using its legs; unlike in arthropods, both legs of a pair... | Onychophora | Wikipedia | 511 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
When assessing other individuals, individuals often measure one another up by running their antennae down the length of the other individual. Once hierarchy has been established, pairs of individuals will often cluster together to form an "aggregate"; this is fastest in male-female pairings, followed by pairs of female... | Onychophora | Wikipedia | 483 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Onychophora probably do not primarily use vision to detect their prey; although their tiny eyes do have a good image-forming capacity, their forward vision is obscured by their antennae; their nocturnal habit also limits the utility of eyesight. Air currents, formed by prey motion, are thought to be the primary mode of... | Onychophora | Wikipedia | 177 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Velvet worms literally creep up on their prey, with their smooth, gradual and fluid movement escaping detection. Once they reach their prey, they touch it very softly with their antennae to assess its size and nutritional value. After each poke, the antenna is hastily retracted to avoid alerting the prey. This investig... | Onychophora | Wikipedia | 472 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Reproduction and life-cycle
Almost all species of velvet worm reproduce sexually. The sole exception is Epiperipatus imthurni, of which no males have been observed; reproduction instead occurs by parthenogenesis. All species are in principle sexually distinct and bear, in many cases, a marked sexual dimorphism: the fem... | Onychophora | Wikipedia | 216 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The detailed process by which this is achieved is in most cases still unknown, a true penis having been observed only in species of the genus Paraperipatus. In many Australian species, there exist dimples or special dagger- or axe-shaped structures on the head; the male of Florelliceps stutchburyae presses a long spine... | Onychophora | Wikipedia | 411 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Ovipary occurs solely in the Peripatopsidae, often in regions with erratic food supply or unsettled climate. In these cases, the yolk-rich eggs measure 1.3 to 2.0 mm and are coated in a protective chitinous shell. Maternal care is unknown.
The majority of species are ovoviviparous: the medium-sized eggs, encased only b... | Onychophora | Wikipedia | 468 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Ecology
The velvet worm's important predators are primarily various spiders and centipedes, along with rodents and birds, such as, in Central America, the clay-coloured thrush (Turdus grayi). In South America, Hemprichi's coral snake (Micrurus hemprichii) feeds almost exclusively on velvet worms. For defence, some spec... | Onychophora | Wikipedia | 384 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The primary threat comes from destruction and fragmentation of velvet worm habitat due to industrialisation, draining of wetlands, and slash-and-burn agriculture. Many species also have naturally low population densities and closely restricted geographic ranges; as a result, relatively small localised disturbances of i... | Onychophora | Wikipedia | 428 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Together, the velvet worms, arthropods, and water bears form a monophyletic taxon, the Panarthropoda, i.e., the three groups collectively cover all descendants of their last common ancestor. Due to certain similarities of form, the velvet worms were usually grouped with the water bears to form the taxon Protoarthropoda... | Onychophora | Wikipedia | 420 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Modern taxonomy does not study criteria such as "higher" and "lower" states of development or distinctions between "main" and "side" branches—only family relationships indicated by cladistic methods are considered relevant. From this point of view, several common characteristics still support the Articulata hypothesis ... | Onychophora | Wikipedia | 369 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Particularly characteristic of the Cycloneuralia is a ring of "circumoral" nerves around the mouth opening, which the proponents of the Ecdysozoa hypothesis also recognise in modified form in the details of the nerve patterns of the Panarthropoda. Both groups also share a common skin-shedding mechanism (ecdysis) and mo... | Onychophora | Wikipedia | 178 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The "stem-group arthropod" hypothesis is very widely accepted, but some trees suggest that the onychophorans may occupy a different position; their brain anatomy is more closely related to that of the chelicerates than to any other arthropod. The modern velvet worms form a monophyletic group, incorporating all the desc... | Onychophora | Wikipedia | 414 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The Peripatidae exhibit a range of derivative features. They are longer, on average, than the Peripatopsidae and also have more legs. The number of leg pairs in this family range from 19 (in Typhloperipatus williamsoni) to 43 (in Plicatoperipatus jamaicensis). The gonopore is always between the penultimate leg pair. No... | Onychophora | Wikipedia | 166 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Evolution
Onychophoran paleontology is plagued by the vagaries of the preservation process that makes fossils difficult to interpret. Experiments on the decay and compaction of onychophora demonstrate difficulties in interpreting fossils; certain parts of living onychophora are visible only in certain conditions:
The ... | Onychophora | Wikipedia | 407 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
The low preservation potential of the non-mineralised onychophorans means that they have a sparse fossil record. The lobopodian Helenodora from the Carboniferous of North America has been suggested to be a member of Onychophora, but other studies recover it as more closely related to other lobopodians. A Late Carbonife... | Onychophora | Wikipedia | 381 | 43198 | https://en.wikipedia.org/wiki/Onychophora | Biology and health sciences | Ecdysozoa | Animals |
Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of about 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration.
The foregut... | Nemertea | Wikipedia | 415 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
All nemerteans move slowly, using their external cilia to glide on surfaces on a trail of slime, while larger species use muscular waves to crawl, and some swim by dorso-ventral undulations. A few live in the open ocean while the rest find or make hiding places on the bottom. About a dozen species inhabit freshwater, m... | Nemertea | Wikipedia | 389 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Traditional taxonomy divides the phylum in two classes, Anopla ("unarmed" – their proboscises do not have a little dagger) with two orders, and Enopla ("armed" with a dagger) also with two orders. However, it is now accepted that Anopla are paraphyletic, as one order of Anopla is more closely related to Enopla than to ... | Nemertea | Wikipedia | 406 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
The typical nemertean body is very thin in proportion to its length. The smallest are a few millimeters long, most are less than , and several exceed . The longest animal ever found, at long, may be a specimen of Lineus longissimus, Ruppert, Fox and Barnes refer to a Lineus longissimus long, washed ashore after a sto... | Nemertea | Wikipedia | 507 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
The mouth is ventral and a little behind the front of the body. The foregut, stomach and intestine run a little below the midline of the body and the anus is at the tip of the tail. Above the gut and separated from the gut by mesenchyme is the rhynchocoel, a cavity which mostly runs above the midline and ends a little ... | Nemertea | Wikipedia | 384 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
In most of the class Enopla, the proboscis exits from a common orifice of the rhynchocoel and mouth. A typical member of this class has a stylet, a calcareous barb, with which the animal stabs the prey many times to inject toxins and digestive secretions. The prey is then swallowed whole or, after partial digestion, it... | Nemertea | Wikipedia | 446 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
In the simplest type of circulatory system, two lateral vessels are joined at the ends to form a loop. However, many species have additional long-wise and cross-wise vessels. There is no heart nor pumping vessels, and the flow of fluid depends on contraction of both the vessels and the body wall's muscles. In some spec... | Nemertea | Wikipedia | 450 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Some species have paired cerebral organs, sacs whose only openings are to the outside. Others species have unpaired evertible organs on the front of their heads. Some have slits along the side of the head or grooves obliquely across the head, and these may be associated with paired cerebral organs. All of these are tho... | Nemertea | Wikipedia | 441 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Nemerteans often have numerous temporary gonads (ovaries or testes), forming a row down each side of the body in the mesenchyme. Temporary gonoducts (ducts from which the ova or sperm are emitted), one per gonad, are built when the ova and sperm are ready. The eggs are generally fertilised externally. Some species shed... | Nemertea | Wikipedia | 466 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Most nemerteans are marine animals that burrow in sediments, lurk in crevices between shells, stones or the holdfasts of algae or sessile animals. Some live deep in the open oceans, and have gelatinous bodies. Others build semi-permanent burrows lined with mucus or produce cellophane-like tubes. Mainly in the tropics a... | Nemertea | Wikipedia | 498 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
The few predators on nemerteans include bottom-feeding fish, some sea birds, a few invertebrates including horseshoe crabs, and other nemerteans. Nemerteans' skins secrete toxins that deter many predators, but some crabs may clean nemerteans with one claw before eating them. The American Cerebratulus lacteus and the So... | Nemertea | Wikipedia | 105 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Traditional taxonomic classification has divided the group into two classes and four orders:
Class Anopla ("unarmed"). Includes animals with proboscis without stylet, and a mouth underneath and behind the brain.
Order Palaeonemertea. Comprises 100 marine species. Their body wall has outer circular and inner length-wi... | Nemertea | Wikipedia | 413 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Recent molecular phylogenetic studies divided the group into two superclasses, three classes, and eight orders:
Superclass Pronemertea
Class Palaeonemertea
Order Carinomiformes
Order Tubulaniformes
Order Archinemertea
Superclass Neonemertea
Class Pilidiophora
Order Hubrechtiiformes
Order Heteronemertea
Class Hoplonem... | Nemertea | Wikipedia | 494 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
There is no doubt that the phylum Nemertea is monophyletic (meaning that the phylum includes all and only descendants of one ancestor that was also a member of the phylum). The synapomorphies (trait shared by an ancestor and all its descendants, but not by other groups) include the eversible proboscis located in the rh... | Nemertea | Wikipedia | 303 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Relationships with other phyla
English-language writings have conventionally treated nemerteans as acoelomate bilaterians that are most closely related to flatworms (Platyhelminthes). These pre-cladistics analyses emphasised as shared features: multiciliated (with multiple cilia per cell), glandular epidermis; rod-sha... | Nemertea | Wikipedia | 299 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
According to more recent analyses, in the development of nemertean embryos, ectomesoderm (outer part of the mesoderm, which is the layer in which most of the internal organs are built) is derived from cells labelled 3a and 3b, and endomesoderm (inner part of the mesoderm) is derived from the 4d cell. Some of the ectome... | Nemertea | Wikipedia | 504 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Most protostome phyla outside the Lophotrochozoa are members of Ecdysozoa ("animals that molt"), which include Arthropoda, Nematoda and Priapulida. Most other bilaterian phyla are in the Deuterostomia, which include Echinodermata and Chordata. The Acoelomorpha, which are neither protostomes nor deuterostomes, are regar... | Nemertea | Wikipedia | 102 | 43200 | https://en.wikipedia.org/wiki/Nemertea | Biology and health sciences | Lophotrochozoa | Animals |
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. More than 10,000 species are described in this class. Common r... | Polychaete | Wikipedia | 424 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
The head, or prostomium, is relatively well developed, compared with other annelids. It projects forward over the mouth, which therefore lies on the animal's underside. The head normally includes two to four pair of eyes, although some species are blind. These are typically fairly simple structures, capable of distingu... | Polychaete | Wikipedia | 442 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
A simple but well-developed circulatory system is usually present. The two main blood vessels furnish smaller vessels to supply the parapodia and the gut. Blood flows forward in the dorsal vessel, above the gut, and returns down the body in the ventral vessel, beneath the gut. The blood vessels themselves are contracti... | Polychaete | Wikipedia | 446 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
Polychaetes are predominantly marine, but many species also live in freshwater, and a few in terrestrial environments. They are extremely variable in both form and lifestyle, and include a few taxa that swim among the plankton or above the abyssal plain. Most burrow or build tubes in the sediment, and some live as comm... | Polychaete | Wikipedia | 298 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
Notable polychaetes
One notable polychaete, the Pompeii worm (Alvinella pompejana), is endemic to the hydrothermal vents of the Pacific Ocean. Pompeii worms are among the most heat-tolerant complex animals known.
A recently discovered genus, Osedax, includes a species nicknamed the "bone-eating snot flower".
Another r... | Polychaete | Wikipedia | 462 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
The fertilized eggs typically hatch into trochophore larvae, which float among the plankton, and eventually metamorphose into the adult form by adding segments. A few species have no larval form, with the egg hatching into a form resembling the adult, and in many that do have larvae, the trochophore never feeds, surviv... | Polychaete | Wikipedia | 476 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
Being soft-bodied organisms, the fossil record of polychaetes is dominated by their fossilized jaws, known as scolecodonts, and the mineralized tubes that some of them secrete. Most important biomineralising polychaetes are serpulids, sabellids, and cirratulids. Polychaete cuticle does have some preservation potential;... | Polychaete | Wikipedia | 333 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
Basal or incertae sedis
Family Diurodrilidae
Family Histriobdellidae
Family Nerillidae
Family Parergodrilidae
Family Potamodrilidae
Family Psammodrilidae
Family Spintheridae
Family Protodriloididae
Family Saccocirridae
Order Haplodrili
Order Myzostomida
Family Endomyzostomatidae
Family Asteromyzostomatidae
Family Myzos... | Polychaete | Wikipedia | 503 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
Family Cirratulidae (sometimes placed in Spionida)
Family Ctenodrilidae (sometimes own suborder Ctenodrilida)
Family Fauveliopsidae (sometimes own suborder Fauveliopsida)
Family Flabelligeridae (sometimes suborder Flabelligerida)
Family Flotidae (sometimes included in Flabelligeridae)
Family Poeobiidae (sometimes own s... | Polychaete | Wikipedia | 299 | 43207 | https://en.wikipedia.org/wiki/Polychaete | Biology and health sciences | Lophotrochozoa | null |
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 m... | Priapulida | Wikipedia | 493 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
Anatomy
Priapulids are cylindrical worm-like animals, ranging from 0.2–0.3 to 39 centimetres (0.08–0.12 to 15.35 in) long, with a median anterior mouth quite devoid of any armature or tentacles. The body is divided into a main trunk or abdomen and a somewhat swollen proboscis region ornamented with longitudinal ridges... | Priapulida | Wikipedia | 458 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
The nervous system consists of a nerve ring around the pharynx and a prominent cord running the length of the body with ganglia and longitudinal and transversal neurites consistent with an orthogonal organisation. The nervous system retains a basiepidermal configuration with a connection with the ectoderm, forming part... | Priapulida | Wikipedia | 389 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
Stem-group priapulids are known from the Middle Cambrian Burgess Shale, where their soft-part anatomy is preserved, often in conjunction with their gut contents – allowing a reconstruction of their diets. In addition, isolated microfossils (corresponding to the various teeth and spines that line the pharynx and introve... | Priapulida | Wikipedia | 186 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
Phylum Priapulida Théel 1906
Order Halicryptomorpha Salvini-Plawen 1974 [Adrianov & Malakhov 1995; Salvini-Plawen 1974; Eupriapulida Lemburg, 1999]
Family Halicryptidae Salvini-Plawen 1974
Genus Halicryptus
Species H. higginsi (Shirley & Storch, 1999)
Species H. spinulosus (von Siebold, 1849)
Order Meiopriapulomorpha
F... | Priapulida | Wikipedia | 493 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
Family Chaetostephanidae Por & Bromley 1974 [Chaetostephanidae Salvini-Plawen 1974]
Genus Maccabeus
Species M. cirratus (Malakhov, 1979)
Species M. tentaculatus (Por, 1973) | Priapulida | Wikipedia | 54 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
Extinct groups
Stem-group †Scalidophora
Order †Ancalagonida Adrianov & Malakhov 1995 [Fieldiida Adrianov & Malakhov 1995]
Family †Ancalagonidae Conway Morris 1977
Genus †Ancalagon Conway Morris 1977
Family †Fieldiidae Conway Morris 1977
Genus †Fieldia Walcott 1912
Stem-group †Palaeoscolecida
Family †Selkirkiidae Conwa... | Priapulida | Wikipedia | 189 | 43209 | https://en.wikipedia.org/wiki/Priapulida | Biology and health sciences | Ecdysozoa | Animals |
Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian, and possibly Ediacaran, periods. As of 2023, the majority of workers favor placing Vetulicolians in the stem group of the Chordata, but some continue to favor a more crownward placement as a sister group to the ... | Vetulicolia | Wikipedia | 439 | 43217 | https://en.wikipedia.org/wiki/Vetulicolia | Biology and health sciences | Prehistoric agnathae and early chordates | Animals |
Because all vetulicolians had mouths which had no features for chewing or grasping, it is assumed that they were not predators. Since vetulicolians possessed gill slits, many researchers regard these organisms as planktivores. The sediment infills in the guts of their fossils have caused some to suggest that they were ... | Vetulicolia | Wikipedia | 368 | 43217 | https://en.wikipedia.org/wiki/Vetulicolia | Biology and health sciences | Prehistoric agnathae and early chordates | Animals |
A 2024 phylogenetic analysis by Mussini and colleagues found vetulicolians to be a paraphyletic group of stem-chordates, lying outside a clade formed by Yunnanozoon, Cathaymyrus, Pikaia and crown-chordates. This is in part due to the Cambroernida, which are basal stem-ambulacrarians, being discovered to share characte... | Vetulicolia | Wikipedia | 423 | 43217 | https://en.wikipedia.org/wiki/Vetulicolia | Biology and health sciences | Prehistoric agnathae and early chordates | Animals |
Phylum Vetulicolia
? Genus Alienum
A. velamenus
Genus Shenzianyuloma
S. yunnanense
Class Heteromorphida (= Banffozoa )
"Form A"
Order Banffiata
Family Banffiidae
Genus Banffia
B. constricta
B. episoma
Genus Heteromorphus
H. confusus (= Banffia confusa) ; = H. longicaudatus )
Genus Skeemella ... | Vetulicolia | Wikipedia | 490 | 43217 | https://en.wikipedia.org/wiki/Vetulicolia | Biology and health sciences | Prehistoric agnathae and early chordates | Animals |
Some workers have questioned the inclusion of Banffozoa within this group due to their lack of gill slits and apparent gut diverticula, and have theorized that they may fit within Protostomia instead. Skeemella, in particular, has been noted as having striking arthropod-like characteristics. However, Herpetogaster, the... | Vetulicolia | Wikipedia | 367 | 43217 | https://en.wikipedia.org/wiki/Vetulicolia | Biology and health sciences | Prehistoric agnathae and early chordates | Animals |
In probability theory, a probability space or a probability triple is a mathematical construct that provides a formal model of a random process or "experiment". For example, one can define a probability space which models the throwing of a .
A probability space consists of three elements:
A sample space, , which is ... | Probability space | Wikipedia | 414 | 43325 | https://en.wikipedia.org/wiki/Probability%20space | Mathematics | Probability | null |
A probability space is a mathematical triplet that presents a model for a particular class of real-world situations.
As with other models, its author ultimately defines which elements , , and will contain.
The sample space is the set of all possible outcomes. An outcome is the result of a single execution of the m... | Probability space | Wikipedia | 341 | 43325 | https://en.wikipedia.org/wiki/Probability%20space | Mathematics | Probability | null |
The probability measure is a set function returning an event's probability. A probability is a real number between zero (impossible events have probability zero, though probability-zero events are not necessarily impossible) and one (the event happens almost surely, with almost total certainty). Thus is a function T... | Probability space | Wikipedia | 214 | 43325 | https://en.wikipedia.org/wiki/Probability%20space | Mathematics | Probability | null |
Not every subset of the sample space must necessarily be considered an event: some of the subsets are simply not of interest, others cannot be "measured". This is not so obvious in a case like a coin toss. In a different example, one could consider javelin throw lengths, where the events typically are intervals like "... | Probability space | Wikipedia | 369 | 43325 | https://en.wikipedia.org/wiki/Probability%20space | Mathematics | Probability | null |
Keratin () is one of a family of structural fibrous proteins also known as scleroproteins. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, and the outer layer of skin among vertebrates. Keratin also pro... | Keratin | Wikipedia | 453 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
The harder beta-keratins (β-keratins) are found only in the sauropsids, that is all living reptiles and birds. They are found in the nails, scales, and claws of reptiles, in some reptile shells (Testudines, such as tortoise, turtle, terrapin), and in the feathers, beaks, and claws of birds. These keratins are formed pr... | Keratin | Wikipedia | 447 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
Protein structure
The first sequences of keratins were determined by Israel Hanukoglu and Elaine Fuchs (1982, 1983). These sequences revealed that there are two distinct but homologous keratin families, which were named type I and type II keratins. By analysis of the primary structures of these keratins and other inte... | Keratin | Wikipedia | 430 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
Disulfide bridges
In addition to intra- and intermolecular hydrogen bonds, the distinguishing feature of keratins is the presence of large amounts of the sulfur-containing amino acid cysteine, required for the disulfide bridges that confer additional strength and rigidity by permanent, thermally stable crosslinking—in ... | Keratin | Wikipedia | 493 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
Cornification
Cornification is the process of forming an epidermal barrier in
stratified squamous epithelial tissue. At the cellular level,
cornification is characterised by:
production of keratin
production of small proline-rich (SPRR) proteins and transglutaminase which eventually form a cornified cell envelope be... | Keratin | Wikipedia | 482 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
Silk found in insect pupae, and in spider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates. The structure of the spinnerets on spiders' tails, and the contributions of their interior glands, provide remarkable control of fast extrusion. Spider ... | Keratin | Wikipedia | 415 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
Diagnostic use
Keratin expression is helpful in determining epithelial origin in anaplastic cancers. Tumors that express keratin include carcinomas, thymomas, sarcomas and trophoblastic neoplasms. Furthermore, the precise expression-pattern of keratin subtypes allows prediction of the origin of the primary tumor when a... | Keratin | Wikipedia | 133 | 43377 | https://en.wikipedia.org/wiki/Keratin | Biology and health sciences | Proteins | Biology |
The ballista (Latin, from Greek βαλλίστρα ballistra and that from βάλλω ballō, "throw"), plural ballistae or ballistas, sometimes called bolt thrower, was an ancient missile weapon that launched either bolts or stones at a distant target.
Developed from earlier Greek weapons, it relied upon different mechanics, using ... | Ballista | Wikipedia | 448 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
The Greek ballista was a siege weapon. All components that were not made of wood were transported in the baggage train. It would be assembled with local wood, if necessary. Some were positioned inside large, armored, mobile siege towers or even on the edge of a battlefield. For all of the tactical advantages offered, i... | Ballista | Wikipedia | 497 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
Early Roman ballistae
The early Roman ballistae were made of wood, and held together with iron plates around the frames and iron nails in the stand. The main stand had a slider on the top, into which were loaded the bolts or stone shot. Attached to this, at the back, was a pair of 'winches' and a 'claw', used to ratch... | Ballista | Wikipedia | 453 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
Seeing this, Caesar ordered the warships – which were swifter and easier to handle than the transports, and likely to impress the natives more by their unfamiliar appearance – to be removed a short distance from the others, and then be rowed hard and run ashore on the enemy’s right flank, from which position men on dec... | Ballista | Wikipedia | 496 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
During the 6th century, Procopius described the effects of this weapon:
But Belisarius placed upon the towers engines which they call "ballistae". Now these engines have the form of a bow, but on the under side of them a grooved wooden shaft projects; this shaft is so fitted to the bow that it is free to move, and rest... | Ballista | Wikipedia | 486 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
It has been speculated that the Roman military may have also fielded a 'repeating' ballista, also known as a polybolos. Reconstruction and trials of such a weapon carried out in a BBC documentary, What the Romans Did For Us, showed that they "were able to shoot eleven bolts a minute, which is almost four times the rate... | Ballista | Wikipedia | 450 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
Sites across the empire have yielded information on ballistae, from Spain (the Ampurias Catapult), to Italy (the Cremona Battleshield, which proved that the weapons had decorative metal plates to shield the operators), to Iraq (the Hatra Machine) and even Scotland (Burnswark siege tactics training camp), and many other... | Ballista | Wikipedia | 417 | 43379 | https://en.wikipedia.org/wiki/Ballista | Technology | Artillery and siege | null |
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