Karyorelictea is a class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, Loxodes, is found in freshwater.
The majority of karyorelict taxa have not been cultivated in the laboratory, although clonal lines of Loxodes have been developed.
According to Lynn (2008), the Karyorelictea class is divided into three orders:[2]
These three orders were defined morphologically, and have been confirmed with molecular phylogenetics.[3]
An additional family, Wilbertomorphidae, is of uncertain affiliation and has not been assigned to an order.[4]
All ciliates, including karyorelicteans, possess two different kinds of nucleus, which separate the functions of gene expression and sexual recombination. The macronuclei, or somatic nuclei, are the site of transcription, while the smaller micronuclei, or germline nuclei, are only active during sexual reproduction, where they first undergo meiosis to form gametic nuclei, which are exchanged when two mating cells conjugate. Two gametic nuclei fuse to form a zygotic nucleus, which divides by mitosis into two daughter nuclei, one of which develops into a new micronucleus and the other into a macronucleus; the old macronucleus typically disintegrates (see main article).
In most ciliates, a macronucleus can divide during asexual reproduction to form new daughter macronuclei, through a process called amitosis. However, in karyorelicteans, the macronuclei are unable to divide. Instead, they must be produced by division and differentiation of a micronucleus every time, even during asexual reproduction.[5][6]
Because of their non-dividing somatic macronuclei, the karyorelicteans were thought to represent an intermediate evolutionary stage between the hypothetical ancestor of ciliates that did not have nuclear dualism, and the other more "advanced" ciliates which had both nuclear dualism and macronuclei that could divide by amitosis. The name of the group therefore makes reference to their supposedly "primitive" nuclei.[7] This theory has since been superseded, as molecular phylogenies have shown that the karyorelicteans are not the most "primitive" or basally-branching group of ciliates.[8]
Almost all karyorelictean species, except Loxodes, have been described from the marine interstitial habitat, where they live in the pore-water spaces between sediment grains.[9] Animals from such habitats are known as meiofauna, and karyorelicteans have many morphological similarities to meiofaunal animals despite being protists: most karyorelicteans are relatively large (1 mm or more in length), have a worm-like (vermiform) body shape with an elongated tail, and exhibit thigmotactic behavior.[10] Most karyorelicteans feed on bacteria or algae, and prefer microaerobic conditions.[11][12][13] However, one genus, Kentrophoros, lacks an oral apparatus and feeds instead on symbiotic sulfur-oxidizing bacteria that are attached to one side of the cell.[14][15]
The class name Karyorelictea derives from the ancient greek κάρυον (káruon), meaning "hard-shelled seed, or nucleus",[16][17] and from the Latin relictus, meaning 'abandoned'.[18]
An alternative genetic code is used by the nuclear genome of some karyorelictid ciliates (e.g. Parduczia sp.).[19] This code corresponds to translation table 27 and involves the reassignment of three codons:
UAA into Gln (Q) ;UAG into Gln (Q) ;UGA into Trp (W) or Termination (*).Karyorelictea is a class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, Loxodes, is found in freshwater.
The majority of karyorelict taxa have not been cultivated in the laboratory, although clonal lines of Loxodes have been developed.
Karyorelictea es una clase de protistas del filo Ciliophora.[2][3] Tienen forma vermiforme, pues son largos y aplanados, extremadamente contráctiles, excepto en Loxodida. Los miembros de este grupo se caracterizan por no poder replicar el macronúcleo, un proceso denominado amitosis, por lo que este debe ser resintetizado a partir del micronúcleo en cada división celular.[4] La clase se divide en tres órdenes, definidos inicialmente morfológicamente, pero que han sido confirmados por análisis moleculares.
Karyorelictea es una clase de protistas del filo Ciliophora. Tienen forma vermiforme, pues son largos y aplanados, extremadamente contráctiles, excepto en Loxodida. Los miembros de este grupo se caracterizan por no poder replicar el macronúcleo, un proceso denominado amitosis, por lo que este debe ser resintetizado a partir del micronúcleo en cada división celular. La clase se divide en tres órdenes, definidos inicialmente morfológicamente, pero que han sido confirmados por análisis moleculares.
Os Karyorelictea son unha clase de protozoos ciliados caracterizados pola súa incapacidade de replicar o seu macronúcleo, un proceso chamado amitose que realizan outros ciliados. O macronúcleo debe ser resintetizado a partir do micronúcleo en cada división celular.[2] Todos os ciliados posúen varios núcleos dimórficos que teñen diferentes funcións, uns utilízanse para expresar as proteínas e denomínanse macronúcleos ou núcleos somáticos, e outros teñen a función de replicar o ADN herdable e denomínanse micronúcleos ou núcleos da liña xerminal. A maioría dos Karyorelictea non se poden cultivar, aínda que se desenvolveron liñas clonais de Loxodes. A clase está dividida en tres ordes, que son: Protostomatida, Loxodida e Protoheterotrichida, os cales foron inicialmente definidos polas súas características morfolóxicas, pero despois esta división foi confirmada pola filoxenética molecular.[2]
Os Karyorelictea son unha clase de protozoos ciliados caracterizados pola súa incapacidade de replicar o seu macronúcleo, un proceso chamado amitose que realizan outros ciliados. O macronúcleo debe ser resintetizado a partir do micronúcleo en cada división celular. Todos os ciliados posúen varios núcleos dimórficos que teñen diferentes funcións, uns utilízanse para expresar as proteínas e denomínanse macronúcleos ou núcleos somáticos, e outros teñen a función de replicar o ADN herdable e denomínanse micronúcleos ou núcleos da liña xerminal. A maioría dos Karyorelictea non se poden cultivar, aínda que se desenvolveron liñas clonais de Loxodes. A clase está dividida en tres ordes, que son: Protostomatida, Loxodida e Protoheterotrichida, os cales foron inicialmente definidos polas súas características morfolóxicas, pero despois esta división foi confirmada pola filoxenética molecular.
Karyorelictea is een klasse van trilhaardiertjes. Karyorelictea is een van de twee klassen in de onderstam Postciliodesmatophora de andere is Heterotrichea. De klasse omvat drie ordes en twee geslachten waarvan de classificatie nog niet duidelijk is (Incertae sedis).[1]
Karyorelictea is een klasse van trilhaardiertjes. Karyorelictea is een van de twee klassen in de onderstam Postciliodesmatophora de andere is Heterotrichea. De klasse omvat drie ordes en twee geslachten waarvan de classificatie nog niet duidelijk is (Incertae sedis).
원시대핵류(Karyorelictea)는 섬모충류의 일종이다.[2] 대부분의 종이 해양 모래 틈 서식지에 발견되는 소형 저서동물이지만 록소데스속(Loxodes) 종만은 민물에서 발견된다.
