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48-397: Isopoda is an order of crustaceans . Members of this group are called isopods and include both aquatic species, and terrestrial species such as woodlice . All have rigid, segmented exoskeletons , two pairs of antennae , seven pairs of jointed limbs on the thorax , and five pairs of branching appendages on the abdomen that are used in respiration . Females brood their young in

96-407: A ball as a defense mechanism or to conserve moisture like species in the family Armadillididae , the pillbugs. There are over 10,000 identified species of isopod worldwide, with around 4,500 species found in marine environments, mostly on the seabed, 500 species in fresh water, and another 5,000 species on land. The order is divided into eleven suborders . The fossil record of isopods dates back to

144-409: A ball when threatened, a feature that has evolved independently in different groups and also in the marine sphaeromatids . Isopods have a simple gut which lacks a midgut section; instead there are caeca connected to the back of the stomach in which absorption takes place. Food is sucked into the esophagus , a process enhanced in the blood-sucking parasitic species, and passed by peristalsis into

192-519: A particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognized only rarely. The name of an order is usually written with a capital letter. For some groups of organisms, their orders may follow consistent naming schemes . Orders of plants , fungi , and algae use

240-425: A pest, endangering the fish and possibly injuring the aquarium keeper. Some members of the family Cirolanidae suck the blood of fish, and others, in the family Aegidae , consume the blood, fins, tail and flesh and can kill the fish in the process. The World Marine, Freshwater and Terrestrial Isopod Crustaceans database subdivides the order into eleven suborders: Isopods first appeared in the fossil record during

288-400: A post-larval stage which resembles the adult except for the absence of the last pair of pereopods. The lack of a swimming phase in the life cycle is a limiting factor in isopod dispersal , and may be responsible for the high levels of endemism in the order. As adults, isopods differ from other crustaceans in that moulting occurs in two stages known as "biphasic moulting". First they shed

336-536: A pouch under their thorax called the marsupium . Isopods have various feeding methods: some eat dead or decaying plant and animal matter, others are grazers or filter feeders , a few are predators , and some are internal or external parasites , mostly of fish. Aquatic species mostly live on the seabed or the bottom of freshwater bodies of water , but some taxa can swim for short distance. Terrestrial forms move around by crawling and tend to be found in cool, moist places. Some species are able to roll themselves into

384-529: A similar appearance as a result of convergent evolution or even mimicry . In addition, there can be morphological differences within a species, such as in Apoica flavissima where queens are significantly smaller than workers. A further problem with relying on morphological data is that what may appear morphologically to be two distinct species may in fact be shown by DNA analysis to be a single species. The significance of these differences can be examined through

432-465: A swelling on the oviduct close to the gonopore. Fertilisation only takes place when the eggs are shed soon after a moult, at which time a connection is established between the semen receptacle and the oviduct. The eggs, which may number up to several hundred, are brooded by the female in the marsupium , a chamber formed by flat plates known as oostegites under the thorax. This is filled with water even in terrestrial species. The eggs hatch as mancae ,

480-456: A waxy cuticle, they need to conserve water, often living in a humid environment and sheltering under stones, bark, debris or leaf litter . Desert species, like Hemilepistus reaumuri, are usually nocturnal, spending the day in a burrow and emerging at night. Moisture is achieved through food sources or by drinking, and some species can form their paired uropodal appendages into a tube and funnel water from dewdrops onto their pleopods. In many taxa,

528-428: Is believed to be the first instance discovered of a parasite functionally replacing a host structure in animals. In most species, the sexes are separate and there is little sexual dimorphism , but a few species are hermaphroditic and some parasitic forms show large differences between the sexes. Some Cymothoidans are protandrous hermaphrodites , starting life as males and later changing sex, and some Anthuroideans are

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576-549: Is digested by enzymes secreted in the caeca. Limnoria lignorum , for example, bores into wood and additionally feeds on the mycelia of fungi attacking the timber, thus increasing the nitrogen in its diet. Land-based wood-borers mostly house symbiotic bacteria in the hindgut which aid in digesting cellulose. There are numerous adaptations to this simple gut, but these are mostly correlated with diet rather than by taxonomic group. Parasitic species are mostly external parasites of fish or crustaceans and feed on blood. The larvae of

624-435: Is fused with the first segment of the thorax to form the cephalon . There are two pairs of unbranched antennae , the first pair being vestigial in land-dwelling species. The eyes are compound and unstalked and the mouthparts include a pair of maxillipeds and a pair of mandibles (jaws) with palps (segmented appendages with sensory functions) and lacinia mobilis (spine-like movable appendages). The seven free segments of

672-559: Is in contrast to physiology , which deals primarily with function. Morphology is a branch of life science dealing with the study of the gross structure of an organism or taxon and its component parts. The etymology of the word "morphology" is from the Ancient Greek μορφή ( morphḗ ), meaning "form", and λόγος ( lógos ), meaning "word, study, research". While the concept of form in biology, opposed to function , dates back to Aristotle (see Aristotle's biology ),

720-485: Is said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or evolution. Most taxa differ morphologically from other taxa. Typically, closely related taxa differ much less than more distantly related ones, but there are exceptions to this. Cryptic species are species which look very similar, or perhaps even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire

768-591: Is the primary means of locomotion, and some species bore into the seabed, the ground or timber structures. Some members of the families Sphaeromatidae , Idoteidae and Munnopsidae are able to swim pretty well, and have their front three pairs of pleopods modified for this purpose, with their respiratory structures limited to the hind pleopods. Most terrestrial species are slow-moving and conceal themselves under objects or hide in crevices or under bark. The semi-terrestrial sea slaters ( Ligia spp.) can run rapidly on land and many terrestrial species can roll themselves into

816-659: The Prodromus Systematis Naturalis Regni Vegetabilis of Augustin Pyramus de Candolle and the Genera Plantarum of Bentham & Hooker, it indicated taxa that are now given the rank of family (see ordo naturalis , ' natural order '). In French botanical publications, from Michel Adanson 's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille (plural: familles )

864-760: The Carboniferous period (in the Pennsylvanian epoch ), at least 300 million years ago, when isopods lived in shallow seas. The name Isopoda is derived from the Greek roots iso- (from ἴσος ísos , meaning "equal") and -pod (from ποδ- , the stem of πούς poús , meaning "foot"). Classified within the arthropods , isopods have a chitinous exoskeleton and jointed limbs. Isopods are typically flattened dorsoventrally (broader than they are deep), although many species deviate from this rule, particularly parasitic forms, and those living in

912-703: The Carboniferous period of the Paleozoic some 300 million years ago. They were primitive, short-tailed members of the suborder Phreatoicidea . At that time, Phreatoicideans were marine organisms with a cosmopolitan distribution. Nowadays, the members of this formerly widespread suborder form relic populations in freshwater environments in South Africa, India and Oceania, the greatest number of species being in Tasmania . Other primitive, short-tailed suborders include Asellota , Microcerberidea , Calabozoidea and

960-562: The Gnathiidae family and adult cymothoidids have piercing and sucking mouthparts and clawed limbs adapted for clinging onto their hosts . In general, isopod parasites have diverse lifestyles and include Cancricepon elegans , found in the gill chambers of crabs ; Athelges tenuicaudis , attached to the abdomen of hermit crabs; Crinoniscus equitans living inside the barnacle Balanus perforatus ; cyproniscids , living inside ostracods and free-living isopods; bopyrids , living in

1008-569: The exoskeleton from the posterior part of their body and later shed the anterior part. The giant Antarctic isopod Glyptonotus antarcticus is an exception, and moults in a single process. The majority of crustaceans are aquatic and the isopods are one of the few groups of which some members now live on land. The only other crustaceans which include a small number of terrestrial species are amphipods (like sandhoppers ) and decapods (crabs, shrimp, etc.). Terrestrial isopods play an important role in many tropical and temperate ecosystems by aiding in

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1056-430: The abdominal segments, starting with the sixth segment, is fused to the telson (terminal section) to form a rigid pleotelson . The first five abdominal segments each bear a pair of biramous (branching in two) pleopods ( lamellar structures which serve the function of gas exchange, and in aquatic species serve as gills and propulsion), and the last segment bears a pair of biramous uropods (posterior limbs). In males,

1104-430: The coxae (first segments) are fused to the tergites (dorsal plates) to form epimera (side plates). In mature females, some or all of the limbs have appendages known as oostegites which fold underneath the thorax and form a brood chamber for the eggs. In males, the gonopores (genital openings) are on the ventral surface of segment eight and in the females, they are in a similar position on segment six. One or more of

1152-544: The decomposition of plant material through mechanical and chemical means, and by enhancing the activity of microbes. Macro-detritivores, including terrestrial isopods, are absent from arctic and sub-arctic regions, but have the potential to expand their range with increased temperatures in high latitudes. The woodlice, suborder Oniscidea , are the most successful group of terrestrial crustaceans and show various adaptations for life on land. They are subject to evaporation, especially from their ventral area, and as they do not have

1200-420: The deep sea or in ground water habitats . Their colour may vary, from grey to white, or in some cases red, green, or brown. Isopods vary in size, ranging from some Microcerberidae species of just .3 millimetres (0.012 in) to the deep sea giant isopod Bathynomus spp. of nearly 50 cm (20 in). Giant isopods lack an obvious carapace (shell), which is reduced to a "cephalic shield" covering only

1248-472: The ending -anae that was initiated by Armen Takhtajan 's publications from 1966 onwards. The order as a distinct rank of biological classification having its own distinctive name (and not just called a higher genus ( genus summum )) was first introduced by the German botanist Augustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s. Carl Linnaeus

1296-408: The families Ligiidae and Tylidae , commonly known as rock lice or sea slaters, are the least specialised of the woodlice for life on land. They inhabit the splash zone on rocky shores, jetties and pilings, may hide under debris washed up on the shore and can swim if immersed in water. Order (biology) What does and does not belong to each order is determined by a taxonomist , as is whether

1344-910: The field of zoology , the Linnaean orders were used more consistently. That is, the orders in the zoology part of the Systema Naturae refer to natural groups. Some of his ordinal names are still in use, e.g. Lepidoptera (moths and butterflies) and Diptera (flies, mosquitoes, midges, and gnats). In virology , the International Committee on Taxonomy of Viruses 's virus classification includes fifteen taxomomic ranks to be applied for viruses , viroids and satellite nucleic acids : realm , subrealm , kingdom , subkingdom, phylum , subphylum , class, subclass, order, suborder, family, subfamily , genus, subgenus , and species. There are currently fourteen viral orders, each ending in

1392-416: The field of morphology was developed by Johann Wolfgang von Goethe (1790) and independently by the German anatomist and physiologist Karl Friedrich Burdach (1800). Among other important theorists of morphology are Lorenz Oken , Georges Cuvier , Étienne Geoffroy Saint-Hilaire , Richard Owen , Carl Gegenbaur and Ernst Haeckel . In 1830, Cuvier and Saint-Hilaire engaged in a famous debate , which

1440-452: The gill chambers or on the carapace of shrimps and crabs and causing a characteristic bulge which is even recognisable in some fossil crustaceans; and entoniscidae living inside some species of crab and shrimp. Cymothoa exigua is a parasite of the spotted rose snapper Lutjanus guttatus in the Gulf of California ; it causes the tongue of the fish to atrophy and takes its place in what

1488-521: The head. This means that the gill -like structures, which in other related groups are protected by the carapace, are instead found on specialised limbs on the abdomen. The dorsal (upper) surface of the animal is covered by a series of overlapping, articulated plates which give protection while also providing flexibility. The isopod body plan consists of a head (cephalon), a thorax (pereon) with seven segments (pereonites), and an abdomen (pleon) with six segments (pleonites), some of which may be fused. The head

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1536-401: The presence of a special chamber under the thorax for brooding eggs. They have a cosmopolitan distribution and over 10,000 species of isopod, classified into 11 suborders, have been described worldwide. Around 4,500 species are found in marine environments, mostly on the sea floor. About 500 species are found in fresh water and another 5,000 species are the terrestrial woodlice , which form

1584-408: The respiratory structures on the endopods are internal, with a spiracle and pseudotrachaea, which resemble lungs. In others, the endopod is folded inside the adjoining exopod (outer branch of the pleopod). Both these arrangements help to prevent evaporation from the respiratory surfaces. Many species can roll themselves into a ball, a behaviour used in defense that also conserves moisture. Members of

1632-405: The reverse, being protogynous hermaphrodites that are born female. Some Gnathiidans males are sessile and live with a group of females. Males have a pair of penises, which may be fused in some species. The sperm is transferred to the female by the modified second pleopod which receives it from the penis and which is then inserted into a female gonopore . The sperm is stored in a special receptacle,

1680-420: The same position. Michael Benton (2005) inserted them between superorder and magnorder instead. This position was adopted by Systema Naturae 2000 and others. In botany , the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order. Any number of further ranks can be used as long as they are clearly defined. The superorder rank is commonly used, with

1728-399: The second pair of pleopods, and sometimes also the first, are modified for use in transferring sperm . The endopods (inner branches of the pleopods) are modified into structures with thin, permeable cuticles (flexible outer coverings) which act as gills for gas exchange . In some terrestrial isopods, these resemble lungs . Isopods belong to the larger group Peracarida , which are united by

1776-457: The short-tailed forms into refugia . The latter are now restricted to environments such as the deep sea, freshwater, groundwater and dry land. Isopods in the suborder Asellota are by far the most species-rich group of deep sea isopods. Unlike the amphipods , marine and freshwater isopods are entirely benthic . This gives them little chance to disperse to new regions and may explain why so many species are endemic to restricted ranges. Crawling

1824-405: The southern hemisphere and may have radiated on the ancient supercontinent of Gondwana soon after it broke away from Laurasia 200 million years ago. The short-tailed forms may have been driven from the shallow seas in which they lived by increased predatory pressure from marine fish, their main predators. The development of the long-tailed forms may also have provided competition that helped force

1872-908: The stomach, where the material is processed and filtered. The structure of the stomach varies, but in many species there is a dorsal groove into which indigestible material is channelled and a ventral part connected to the caeca where intracellular digestion and absorption take place. Indigestible material passes on through the hindgut and is eliminated through the anus , which is on the pleotelson. Isopods are detritivores , browsers , carnivores (including predators and scavengers ), parasites, and filter feeders , and may occupy one or more of these feeding niches. Only aquatic and marine species are known to be parasites or filter feeders. Some exhibit coprophagia and will also consume their own fecal pellets. Terrestrial species are in general herbivorous, with woodlice feeding on moss, bark, algae, fungi and decaying material. In marine isopods that feed on wood, cellulose

1920-652: The suborder Oniscidea. In the deep sea, members of the suborder Asellota predominate, to the near exclusion of all other isopods, having undergone a large adaptive radiation in that environment. The largest isopod is in the genus Bathynomus and some large species are fished commercially for human food in Mexico , Japan and Hawaii . Some isopod groups have evolved a parasitic lifestyle, particularly as external parasites of fish. They can damage or kill their hosts and can cause significant economic loss to commercial fisheries. In reef aquariums , parasitic isopods can become

1968-777: The suffix -ales (e.g. Dictyotales ). Orders of birds and fishes use the Latin suffix -iformes meaning 'having the form of' (e.g. Passeriformes ), but orders of mammals and invertebrates are not so consistent (e.g. Artiodactyla , Actiniaria , Primates ). For some clades covered by the International Code of Zoological Nomenclature , several additional classifications are sometimes used, although not all of these are officially recognized. In their 1997 classification of mammals , McKenna and Bell used two extra levels between superorder and order: grandorder and mirorder . Michael Novacek (1986) inserted them at

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2016-442: The suffix -virales . Morphology (biology) Morphology in biology is the study of the form and structure of organisms and their specific structural features. This includes aspects of the outward appearance (shape, structure, color, pattern, size), i.e. external morphology (or eidonomy ), as well as the form and structure of internal parts like bones and organs , i.e. internal morphology (or anatomy ). This

2064-447: The terrestrial Oniscidea . The short-tailed isopods have a short pleotelson and terminal, stylus-like uropods and have a sedentary lifestyle on or under the sediment on the seabed. The long-tailed isopods have a long pleotelson and broad lateral uropods which can be used in swimming. They are much more active and can launch themselves off the seabed and swim for short distances. The more advanced long-tailed isopods are mostly endemic to

2112-431: The thorax each bear a pair of unbranched pereopods (limbs). In most species these are used for locomotion and are of much the same size, morphology and orientation, giving the order its name "Isopoda", from the Greek equal foot . In a few species, the front pair are modified into gnathopods with clawed, gripping terminal segments. The pereopods are not used in respiration, as are the equivalent limbs in amphipods , but

2160-576: The use of allometric engineering in which one or both species are manipulated to phenocopy the other species. A step relevant to the evaluation of morphology between traits/features within species, includes an assessment of the terms: homology and homoplasy . Homology between features indicates that those features have been derived from a common ancestor. Alternatively, homoplasy between features describes those that can resemble each other, but derive independently via parallel or convergent evolution . The invention and development of microscopy enabled

2208-578: The word family ( familia ) was assigned to the rank indicated by the French famille , while order ( ordo ) was reserved for a higher rank, for what in the 19th century had often been named a cohors (plural cohortes ). Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognized by Linnaeus as orders in his natural classification (e.g. Palmae or Labiatae ). Such names are known as descriptive family names. In

2256-551: Was the first to apply it consistently to the division of all three kingdoms of nature (then minerals , plants , and animals ) in his Systema Naturae (1735, 1st. Ed.). For plants, Linnaeus' orders in the Systema Naturae and the Species Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the word ordo was first consistently used for natural units of plants, in 19th-century works such as

2304-561: Was used as a French equivalent for this Latin ordo . This equivalence was explicitly stated in the Alphonse Pyramus de Candolle 's Lois de la nomenclature botanique (1868), the precursor of the currently used International Code of Nomenclature for algae, fungi, and plants . In the first international Rules of botanical nomenclature from the International Botanical Congress of 1905,

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