71-486: The Chaetognatha / k iː ˈ t ɒ ɡ n ə θ ə / or chaetognaths / ˈ k iː t ɒ ɡ n æ θ s / (meaning bristle-jaws ) are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms , they are mostly nektonic ; however about 20% of the known species are benthic , and can attach to algae and rocks . They are found in all marine waters, from surface tropical waters and shallow tide pools to
142-551: A "hop and sink" behaviour, to keep themselves in the desired location in the water layer, and swim actively to catch prey. They all tend to keep the body slightly slanted with the head pointing downwards. They often show a "gliding" behaviour, slowly sinking for a while, and then catching up with a quick movement of their fins. Benthic species usually stay attached to substrates such as rocks, algae or sea grasses, more rarely on top or between sand grains, and act more strictly as ambush predators, staying still until prey passes by. The prey
213-556: A certain degree of morphological or developmental similarity (the phenetic definition), or a group of organisms with a certain degree of evolutionary relatedness (the phylogenetic definition). Attempting to define a level of the Linnean hierarchy without referring to (evolutionary) relatedness is unsatisfactory, but a phenetic definition is useful when addressing questions of a morphological nature—such as how successful different body plans were. The most important objective measure in
284-407: A character unique to a sub-set of the crown group. Furthermore, organisms in the stem group of a phylum can possess the "body plan" of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a distinct body plan. A classification using this definition may be strongly affected by the chance survival of rare groups, which can make
355-434: A dorso-ventral undulating body motion, where their tail fin assists with propulsion and the body fins with stabilization and steering. Muscle movements have been described as among the fastest in metazoans . Muscles are directly excitable by electrical currents or strong K+ solutions; the main neuromuscular transmitter is acetylcholine. All species are hermaphroditic , carrying both eggs and sperm . Each animal possesses
426-407: A few species such as Ferosagitta hispida that attaches eggs to the substrate. In Eukrohnia , eggs develop in marsupial sacs or attached to algae . Eggs usually hatch after 1-3 days. Chaetognaths do not undergo metamorphosis nor they possess a well-defined larval stage, an unusual trait among marine invertebrates; however there are significant morphological differences between the newborn and
497-433: A fish's body. The functional units of the lateral line are the neuromasts, discrete mechanoreceptive organs that sense movement in water. There are two main varieties: canal neuromasts and superficial neuromasts. Superficial neuromasts are on the surface of the body, while canal neuromasts are along the lateral lines in subdermal, fluid-filled canals. Each neuromast consists of receptive hair cells whose tips are covered by
568-428: A flexible hood arising from the neck region when the animal is swimming. Spines and teeth are made of α- chitin , and the head is protected by a chitinous armature. The mouth opens into a muscular pharynx , which contains glands to lubricate the passage of food. From here, a straight intestine runs the length of the trunk to an anus just forward of the tail. The intestine is the primary site of digestion and includes
639-433: A flexible jellylike cupula. Hair cells typically possess both glutamatergic afferent connections and cholinergic efferent connections . The receptive hair cells are modified epithelial cells ; they typically possess bundles of 40–50 microvilli "hairs" which function as the mechanoreceptors. Within each bundle, the hairs are organized in a rough "staircase" from shortest to longest. The hair cells are stimulated by
710-402: A group ("a self-contained unity"): "perhaps such a real and completely self-contained unity is the aggregate of all species which have gradually evolved from one and the same common original form, as, for example, all vertebrates. We name this aggregate [a] Stamm [i.e., stock] ( Phylon )." In plant taxonomy , August W. Eichler (1883) classified plants into five groups named divisions,
781-602: A group containing Viridiplantae and the algal Rhodophyta and Glaucophyta divisions. The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Thus some sources place horsetails in division Arthrophyta and ferns in division Monilophyta, while others place them both in Monilophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes), or for conifers alone as below. Since
SECTION 10
#1732776343352852-501: A hydrological indicator of currents and water masses. All chaetognaths are ambush predators , preying on other planktonic animals, mostly copepods and cladocerans but also amphipods, krill and fish larvae. Adults can feed on younger individuals of the same species. Some species are also reported to be omnivores, feeding on algae and detritus. Chaetognaths are known to use the neurotoxin tetrodotoxin to subdue prey, possibly synthesized by Vibrio bacterial species. The mtDNA of
923-447: A mouth with one or two rows of tiny teeth, compound eyes, and a nervous system, they have no excretory or respiratory systems. While often said to lack a circulatory system, chaetognaths do have a rudimentary hemal system resembling those of annelids . The arrow worm rhabdomeres are derived from microtubules 20 nm long and 50 nm wide, which in turn form conical bodies that contain granules and thread structures. The cone body
994-460: A pair of diverticula near the anterior end. Materials are moved about the body cavity by cilia . Waste materials are simply excreted through the skin and anus. Eukrohniid species possess an oil vacuole closely associated with the gut. This organ contains wax esters which may assist reproduction and growth outside of the production season for Eukrohnia hamata in Arctic seas. Owing to the position of
1065-401: A pair of testes within the tail, and a pair of ovaries in the posterior region of the main body cavity. Immature sperm are released from the testes to mature inside the cavity of the tail, and then swim through a short duct to a seminal vesicle where they are packaged into a spermatophore . During mating, each individual places a spermatophore onto the neck of its partner after rupture of
1136-400: A phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen (as Haeckel had done a century earlier). The definition was posited because extinct organisms are hardest to classify: they can be offshoots that diverged from a phylum's line before the characters that define the modern phylum were all acquired. By Budd and Jensen's definition, a phylum is defined by
1207-471: A phylum much more diverse than it would be otherwise. Total numbers are estimates; figures from different authors vary wildly, not least because some are based on described species, some on extrapolations to numbers of undescribed species. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. The kingdom Plantae
1278-706: A phylum, other phylum-level ranks appear, such as the case of Bacillariophyta (diatoms) within Ochrophyta . These differences became irrelevant after the adoption of a cladistic approach by the ISP, where taxonomic ranks are excluded from the classifications after being considered superfluous and unstable. Many authors prefer this usage, which lead to the Chromista-Protozoa scheme becoming obsolete. Currently there are 40 bacterial phyla (not including " Cyanobacteria ") that have been validly published according to
1349-401: A set of characters shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members. Also, this definition is based on an arbitrary point of time: the present. However, as it is character based, it is easy to apply to the fossil record. A greater problem is that it relies on
1420-401: A subjective decision about which groups of organisms should be considered as phyla. The approach is useful because it makes it easy to classify extinct organisms as " stem groups " to the phyla with which they bear the most resemblance, based only on the taxonomically important similarities. However, proving that a fossil belongs to the crown group of a phylum is difficult, as it must display
1491-424: A term that remains in use today for groups of plants, algae and fungi. The definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier . Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan . At its most basic, a phylum can be defined in two ways: as a group of organisms with
SECTION 20
#17327763433521562-437: A transmitter. They are crucial participants in a corollary discharge system designed to limit self-generated interference. When a fish moves, it creates disturbances in the water that could be detected by the lateral line system, potentially interfering with the detection of other biologically relevant signals. To prevent this, an efferent signal is sent to the hair cell upon motor action, resulting in inhibition which counteracts
1633-474: Is a paraphyletic taxon, which is less acceptable to present-day biologists than in the past. Proposals have been made to divide it among several new kingdoms, such as Protozoa and Chromista in the Cavalier-Smith system . Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. Many of the phyla listed below are used by
1704-437: Is composed of two distinct functional domains: the anterior neuropil domain and the posterior neuropil domain. The former probably controls head muscles moving the spines and the digestive system. The latter is linked to eyes and the corona ciliata. A putative sensory structure of unknown function, the retrocerebral organ, is also hosted by the posterior neuropil domain. The dorsal ganglion is the largest, but nerves extend from all
1775-596: Is created, inducing a flow in the canal fluid. This moves the cupulae of the neuromasts in the canal, resulting in a deflection of the hairs in the direction of the flow. The mechanoreceptive hair cells of the lateral line structure are integrated into more complex circuits through their afferent and efferent connections. The synapses that directly participate in the transduction of mechanical information are excitatory afferent connections that utilize glutamate . Species vary in their neuromast and afferent connections, providing differing mechanoreceptive properties. For instance,
1846-405: Is defined in various ways by different biologists (see Current definitions of Plantae ). All definitions include the living embryophytes (land plants), to which may be added the two green algae divisions, Chlorophyta and Charophyta , to form the clade Viridiplantae . The table below follows the influential (though contentious) Cavalier-Smith system in equating "Plantae" with Archaeplastida ,
1917-539: Is derived from a cilium . The trunk bears one or two pairs of lateral fins incorporating structures superficially similar to the fin rays of fish, with which they are not homologous . Unlike those of vertebrates, these lateral fins are composed of a thickened basement membrane extending from the epidermis . An additional caudal fin covers the post-anal tail. Two chaetognath species, Caecosagitta macrocephala and Eukrohnia fowleri , have bioluminescent organs on their fins. Chaetognaths swim in short bursts using
1988-423: Is detected thanks to the ciliary fence and tuft organs, sensing vibrations – individuals of Spadella cephaloptera for example will attack a glass or metal probe vibrating at an adequate frequency. To catch prey, arrow worms jump forward with a strong stroke of the tail fin. Once in contact with prey, they withdraw the hood over the grasping spines, so that it forms a cage around the prey and bring it in contact with
2059-404: Is even smaller (11,403 bp) and it shows a similar pattern, lacking 21 of the 22 usually present tRNA genes and featuring only 14 of the 37 genes normally present. Chaetognaths show a unique mitochondrial genomic diversity within individual of the same species. The evolutionary relationships of chaetognaths have long been enigmatic. Charles Darwin remarked that arrow worms were "remarkable for
2130-481: Is generally included in kingdom Fungi, though its exact relations remain uncertain, and it is considered a protozoan by the International Society of Protistologists (see Protista , below). Molecular analysis of Zygomycota has found it to be polyphyletic (its members do not share an immediate ancestor), which is considered undesirable by many biologists. Accordingly, there is a proposal to abolish
2201-486: Is observed in the photic zone of shallow waters. Larger chaetognath species tend to live deeper in water, but spend their juvenile stages higher in the water column. Arrow worms however engage in diel vertical migration , spending the day at lower depths to avoid predators, and coming close to the surface at night. Their position in the water column can depend on light, temperature, salinity, age and food supply. They cannot swim against oceanic currents , and they are used as
Chaetognatha - Misplaced Pages Continue
2272-566: The Bacteriological Code Currently there are 2 phyla that have been validly published according to the Bacteriological Code Other phyla that have been proposed, but not validly named, include: Lateral line The lateral line , also called the lateral line organ ( LLO ), is a system of sensory organs found in fish , used to detect movement, vibration, and pressure gradients in
2343-582: The Canada Basin , chaetognaths alone represent ~13% of the zooplankton biomass. As such, they are ecologically relevant and a key food source for fishes and other predators, including commercially relevant fishes such as mackerel or sardines . 58% of known species are pelagic, while about a third of species are epibenthic or meiobenthic , or inhabit the immediate vicinity of the substrate. Chaetognaths have been recorded up to 5000 and possibly even 6000 meters of depth. The highest density of chaetognaths
2414-565: The Catalogue of Life , and correspond to the Protozoa-Chromista scheme, with updates from the latest (2022) publication by Cavalier-Smith . Other phyla are used commonly by other authors, and are adapted from the system used by the International Society of Protistologists (ISP). Some of the descriptions are based on the 2019 revision of eukaryotes by the ISP. The number of protist phyla varies greatly from one classification to
2485-484: The deep sea and polar regions . Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange . They range in size from 2 to 120 millimetres (0.1 to 4.7 in). Chaetognaths were first recorded by the Dutch naturalist Martinus Slabber in 1775. As of 2021, biologists recognize 133 modern species assigned to over 26 genera and eight families . Despite the limited diversity of species,
2556-431: The electroreceptors called ampullae of Lorenzini . The lateral line system is ancient and basal to the vertebrate clade, as it is found in fishes that diverged over 400 million years ago. The lateral line system allows the detection of movement, vibration, and pressure gradients in the water surrounding an animal. It plays an essential role in orientation, predation, and fish schooling by providing spatial awareness and
2627-558: The orbit of the eye are bigger and around twice as sensitive as those of surface-living fish. One function of schooling may be to confuse the lateral line of predatory fishes. A single prey fish creates a simple particle velocity pattern, whereas the pressure gradients of many closely swimming (schooling) prey fish overlap, creating a complex pattern. This makes it difficult for predatory fishes to identify individual prey through lateral line perception. Lateral lines are usually visible as faint lines of pores running along each side of
2698-497: The Zygomycota phylum. Its members would be divided between phylum Glomeromycota and four new subphyla incertae sedis (of uncertain placement): Entomophthoromycotina , Kickxellomycotina , Mucoromycotina , and Zoopagomycotina . Kingdom Protista (or Protoctista) is included in the traditional five- or six-kingdom model, where it can be defined as containing all eukaryotes that are not plants, animals, or fungi. Protista
2769-401: The ability to navigate in the environment. Analysis has shown that the lateral line system should be an effective passive sensing system able to discriminate between submerged obstacles by their shape. The lateral line allows fish to navigate and hunt in water with poor visibility. The lateral line system enables predatory fishes to detect vibrations made by their prey, and to orient towards
2840-458: The above definitions is the "certain degree" that defines how different organisms need to be members of different phyla. The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group. Even this is problematic because the requirement depends on knowledge of organisms' relationships: as more data become available, particularly from molecular studies, we are better able to determine
2911-524: The adult, with respect to proportions, chitinous structures and fin development. The life spans of chaetognaths are variable but short; the longest recorded was 15 months in Sagitta friderici . Little is known of arrow worms' behaviour and physiology, due to the complexity in culturing them and reconstructing their natural habitat. It is known that they feed more frequently with higher temperatures. Planktonic chaetognaths often must swim continuously, with
Chaetognatha - Misplaced Pages Continue
2982-449: The arrow worm Spadella cephaloptera has been sequenced in 2004, and at the time it was the smallest metazoan mitochondrial genome known, being 11,905 base pairs long (it has now been surpassed by the mitchondrial genome of the ctenophore Mnemiopsis leidyi , which is 10,326 bp long). All mitochondrial tRNA genes are absent. The MT-ATP8 and MT-ATP6 genes are also missing. The mtDNA of Paraspadella gotoi , also sequenced in 2004,
3053-401: The deflection of their hair bundles in the direction of the tallest "hairs" or stereocilia . The deflection allows cations to enter through a mechanically gated channel , causing depolarization or hyperpolarization of the hair cell. Depolarization opens Ca v 1.3 calcium channels in the basolateral membrane . Hair cells use a system of transduction with rate coding to transmit
3124-413: The directionality of a stimulus. The hair cells produce a constant, tonic rate of firing. As mechanical motion is transmitted through water to the neuromast, the cupula bends and is displaced according to the strength of the stimulus. This results in a shift in the cell's ionic permeability. Deflection towards the longest hair results in depolarization of the hair cell, increased neurotransmitter release at
3195-466: The electrosensory lateral line lobe of electric fish . The MON is likely involved in the integration of excitatory and inhibitory parallel circuits to interpret mechanoreceptive information. The use of mechanosensitive hairs is homologous to the functioning of hair cells in the auditory and vestibular systems , indicating a close link between these systems. Due to many overlapping functions and their great similarity in ultrastructure and development,
3266-541: The excitation resulting from reception of the self-generated stimulation. This allows the fish to detect external stimuli without interference from its own movements. Signals from the hair cells are transmitted along lateral neurons to the brain. The area where these signals most often terminate is the medial octavolateralis nucleus (MON), which probably processes and integrates mechanoreceptive information. The deep MON contains distinct layers of basilar and non-basilar crest cells, suggesting computational pathways analogous to
3337-526: The excitatory afferent synapse, and a higher rate of signal transduction . Deflection towards the shorter hair has the opposite effect, hyperpolarizing the hair cell and producing a decreased rate of neurotransmitter release. These electrical impulses are then transmitted along afferent lateral neurons to the brain. While both varieties of neuromasts utilize this method of transduction, their specialized organization gives them different mechanoreceptive capacities. Superficial organs are exposed more directly to
3408-419: The external environment. The organization of the bundles within their organs is seemingly haphazard, incorporating various shapes and sizes of microvilli within bundles. This suggests coarse but wide-ranging detection. In contrast, the structure of canal organs allow canal neuromasts more sophisticated mechanoreception, such as of pressure differentials. As current moves across the pores, a pressure differential
3479-581: The far field as waves. The lateral line system is ancient and basal to the vertebrate clade; it is found in groups of fishes that diverged over 400 million years ago, including the lampreys , cartilaginous fishes , and bony fishes . Most amphibian larvae and some fully aquatic adult amphibians possess mechanosensitive systems comparable to the lateral line. The terrestrial tetrapods have secondarily lost their lateral line organs, which are ineffective when not submerged. The electroreceptive organs, called ampullae of Lorenzini , appearing as pits in
3550-507: The first publication of the APG system in 1998, which proposed a classification of angiosperms up to the level of orders , many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses . Wolf plants Hepatophyta Liver plants Coniferophyta Cone-bearing plant Phylum Microsporidia
3621-463: The ganglia along the length of the body. Chaetognaths have two compound eyes, each consisting of a number of pigment-cup ocelli fused together; some deep-sea and troglobitic species have unpigmented or absent eyes. In addition, there are a number of sensory bristles arranged in rows along the side of the body, where they probably perform a function similar to that of the lateral line in fish. An additional, curved, band of sensory bristles lies over
SECTION 50
#17327763433523692-472: The head and neck. Almost all chaetognaths have "indirect" or "inverted" eyes, according to the orientation of photoreceptor cells; only some Eukhroniidae species have "direct" or "everted" eyes. A unique feature of the chaetognath eye is the lamellar structure of photoreceptor membranes, containing a grid of 35–55 nm wide circular pores. A significant mechanosensory system, composed of ciliary receptor organs, detects vibrations, allowing chaetognaths to detect
3763-552: The lateral line system and the inner ear of fish are often grouped together as the octavolateralis system (OLS). Here, the lateral line system detects particle velocities and accelerations with frequencies below 100 Hz. These low frequencies create large wavelengths, which induce strong particle accelerations in the near field of swimming fish that do not radiate into the far field as acoustic waves due to an acoustic short circuit . The auditory system detects pressure fluctuations with frequencies above 100 Hz that propagate to
3834-452: The mouth. They swallow their prey whole. Chaetognaths are found in all world's oceans, from the poles to tropics, and also in brackish and estuarine waters. They inhabit very diverse environments, from hydrothermal vents to deep ocean seafloor, to seagrass beds and marine caves. The majority are planktonic, and they are often the second most common component of zooplankton , with a biomass ranging between 10 and 30% that of copepods . In
3905-411: The next. The Catalogue of Life includes Rhodophyta and Glaucophyta in kingdom Plantae, but other systems consider these phyla part of Protista. In addition, less popular classification schemes unite Ochrophyta and Pseudofungi under one phylum, Gyrista , and all alveolates except ciliates in one phylum Myzozoa , later lowered in rank and included in a paraphyletic phylum Miozoa . Even within
3976-489: The number of individuals is large. Arrow worms are strictly related to and possibly belonging to Gnathifera , a clade of protostomes that do not belong to either Ecdysozoa or Lophotrochozoa . Chaetognaths are transparent or translucent dart-shaped animals covered by a cuticle . They range in length between 1.5 mm to 105 mm in the Antarctic species Pseudosagitta gazellae . Body size, either between individuals in
4047-857: The obscurity of their affinities". Chaetognaths in the past have been traditionally, but erroneously, classed as deuterostomes by embryologists due to deuterostome-like features in the embryo. Lynn Margulis and K. V. Schwartz placed chaetognaths in the deuterostomes in their Five Kingdom classification. However, several developmental features are at odds with deuterostomes and are either akin to Spiralia or unique to Chaetognatha. Gnathostomulida Micrognathozoa Chaetognatha Seisonida Acanthocephala Bdelloidea Monogononta Platytrochozoa Ctenophora Porifera Cnidaria Placozoa Xenacoelomorpha Deuterostomia Ecdysozoa Lophotrochozoa Gnathifera Chaetognatha Molecular phylogeny shows that Chaetognatha are, in fact, protostomes . Thomas Cavalier-Smith places them in
4118-410: The oil vacuole in the center of the tractus, the organ may also have implications for buoyancy, trim and locomotion. Usually chaetognaths are not pigmented, however the intestines of some deep-sea species contain orange-red carotenoid pigments. The nervous system is reasonably simple and shows a typical protostome anatomy, consisting of a ganglionated nerve ring surrounding the pharynx. The brain
4189-539: The other hand, the highly parasitic phylum Mesozoa was divided into two phyla ( Orthonectida and Rhombozoa ) when it was discovered the Orthonectida are probably deuterostomes and the Rhombozoa protostomes . This changeability of phyla has led some biologists to call for the concept of a phylum to be abandoned in favour of placing taxa in clades without any formal ranking of group size. A definition of
4260-417: The protostomes before they evolved their distinctive protostome embryonic characters, they might have retained deuterostome characters inherited from early bilaterian ancestors. Thus chaetognaths may be a useful model for the ancestral bilaterian. Studies of arrow worms' nervous systems suggests they should be placed within the protostomes. According to 2017 and 2019 papers, chaetognaths either belong to or are
4331-445: The protostomes in his Six Kingdom classification. The similarities between chaetognaths and nematodes mentioned above may support the protostome thesis—in fact, chaetognaths are sometimes regarded as a basal ecdysozoan or lophotrochozoan . Chaetognatha appears close to the base of the protostome tree in most studies of their molecular phylogeny. This may explain their deuterostome embryonic characters. If chaetognaths branched off from
SECTION 60
#17327763433524402-482: The relationships among phyla within larger clades like Ecdysozoa and Embryophyta . The term phylum was coined in 1866 by Ernst Haeckel from the Greek phylon ( φῦλον , "race, stock"), related to phyle ( φυλή , "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as
4473-475: The relationships between groups. So phyla can be merged or split if it becomes apparent that they are related to one another or not. For example, the bearded worms were described as a new phylum (the Pogonophora) in the middle of the 20th century, but molecular work almost half a century later found them to be a group of annelids , so the phyla were merged (the bearded worms are now an annelid family ). On
4544-412: The same species or between different species, seems to increase with decreasing temperature. The body is divided into a distinct head, trunk, and tail. About 80% of the body is occupied by primary longitudinal muscles . There are between four and fourteen hooked, grasping spines on each side of their head, flanking a hollow vestibule containing the mouth. The spines are used in hunting, and covered with
4615-629: The seminal vesicle. The sperm rapidly escape from the spermatophore and swim along the midline of the animal until they reach a pair of small pores just in front of the tail. These pores connect to the oviducts , into which the developed eggs have already passed from the ovaries, and it is here that fertilisation takes place. The seminal receptacles and oviducts accumulate and store spermatozoa, to perform multiple fertilisation cycles. Some benthic members of Spadellidae are known to have elaborate courtship rituals before copulation, for example Paraspadella gotoi . The eggs are mostly planktonic, except in
4686-423: The sister group of Gnathifera . Below is a consensus evolutionary tree of Chaetognatha, based on both morphological and molecular data, as of 2021. Heterokrohniidae Eukrohniidae Spadellidae Krohnittidae Phylum In biology , a phylum ( / ˈ f aɪ l əm / ; pl. : phyla ) is a level of classification or taxonomic rank below kingdom and above class . Traditionally, in botany
4757-466: The source to begin predatory action. Blinded predatory fishes remain able to hunt, but not when lateral line function is inhibited by cobalt ions . The lateral line plays a role in fish schooling. Blinded Pollachius virens were able to integrate into a school, whereas fish with severed lateral lines could not. It may have evolved further to allow fish to forage in dark caves. In Mexican blind cave fish, Astyanax mexicanus , neuromasts in and around
4828-424: The superficial neuromasts of the midshipman fish , Porichthys notatus , are sensitive to specific stimulation frequencies. One variety is attuned to collect information about acceleration, at stimulation frequencies between 30 and 200 Hz. The other type obtains information about velocity, and is most receptive to stimulation below 30 Hz. The efferent synapses to hair cells are inhibitory and use acetylcholine as
4899-442: The surrounding water. The sensory ability is achieved via modified epithelial cells , known as hair cells , which respond to displacement caused by motion and transduce these signals into electrical impulses via excitatory synapses . Lateral lines play an important role in schooling behavior, predation, and orientation. Early in the evolution of fish , some of the sensory organs of the lateral line were modified to function as
4970-402: The swimming motion of potential prey. Another organ on the dorsal part of the neck, the corona ciliata, is probably involved in chemoreception. The body cavity is lined by peritoneum , and therefore represents a true coelom , and is divided into one compartment on each side of the trunk, and additional compartments inside the head and tail, all separated completely by septa. Although they have
5041-474: The term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla, the plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering
#351648