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Os mastigonemas están feitos de [[glicoproteína]]s producidas no [[retículo endoplasmático]] da célula e transportados á superficie do flaxelo anterior. Cando se move o flaxelo con forma de grinalda, os mastigonemas crean unha corrente retrógrada, que impulsa a célula pola auga ou arrastra a comida. Os mastigonemas teñen unha estrutura tripartita peculiar, que pode considerarse un carácter definitorio das heterocontas, polo que no grupo se inclúen uns poucos [[protista]]s con esta característica que non producen células coa típica forma heteroconta. Os mastigonemas perdéronse nunhas poucas liñas de heterocontas, principalmente nas [[diatomea]]s.
== ClassificationClasificación ==
A clasificación das heterocontas varia considerablemente segundo as fontes e a época. Orixinalmente as algas heterocontas eran tratadas como dúas [[división (bioloxía)|divisións]] distintas, primeiro incluídas no [[reino (bioloxía)|reino]] [[Plantae]] e despois no [[Protista]]:
As noted above, classification varies considerably. Originally the heterokont algae were treated as two divisions, first within the kingdom Plantae and later the Protista:
DivisionDivisión Chrysophyta
:ClassClase Chrysophyceae ([[goldenalgas algadouradas]]e)
:ClassClase Bacillariophyceae ([[diatomdiatomea]]s)
DivisionDivisión Phaeophyta ([[brownalgas algapardas]]e)
InPorén, thisneste scheme,esquema however, theas Chrysophyceae areson [[paraphyleticparafilético|parafilética]]s todos bothdous other groupsgrupos. AsComo aresultado resultdisto, variousvarios membersmembros haveforon beenclasificados givennas theirsúas ownpropias classes[[clase and(bioloxía)|clases]] oftene divisionsmesmo divisións. RecentOs systemssistemas oftende treatclasificación theserecentes asadoitan classestratar withinestes atres singlegrupos division,domo calledclases dunha soa división, thechamada Heterokontophyta, Chromophyta, orou Ochrophyta. ThisPero isnon nothai universal,un howeveracordo universal: Round ''et al.'', treatpor theexemplo, diatomstrataron as adiatomeas como unha divisiondivisión.
TheO discoverydescubrimento thatde que os [[oomyceteoomiceto]]s ande os [[hyphochytridhifoquitridio]]s areestán relatedrelacionados tocon theseestas algaealgas, ratheren thanvez fungi,de ascos previouslyfungos thought,como hasse ledpensaba manyantes, authorsfixo toque includemoitos theseautores twoincluísen groupsestes amongdous thegrupos entre as heterokontsheterocontas. Should it turn out that they evolved from colored ancestors, the heterokont group would be paraphyletic in their absence. Once againPorén, howeverunha vez máis, usageo uso variesvaría. [[David J. Patterson]] named this extended group the stramenopiles, characterized by the presence of tripartite mastigonemes, [[mitochondrion|mitochondria]] with tubular [[crista]]e, and open [[mitosis]]. He used the stramenopiles as a prototype for a classification without Linnaean rank. Their composition has been essentially stable, but their use within ranked systems varies.
[[Thomas Cavalier-Smith]] treats the heterokonts as identical in composition with the stramenopiles; this is the definition followed here. He has proposed placing them in a separate kingdom [[Chromalveolata]], together with the haptophytes, cryptomonads and alveolates. This is one of the most common revisions to the [[kingdom (biology)|five-kingdom system]], but has not been generally adopted, partly because some biologists doubt their monophyly. A few treat the Chromalveolata as identical in composition with the heterokonts, or list them as a kingdom Stramenopila.
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