# Chordata

| Chordata |
| --- |
|  |
| *Branchiostoma lanceolatum* |
| Klassifikazzjoni xjentifika |
| Dominju: | Eukaryota  |
| Renju: | Animalia  |
| Sottorenju: | Eumetazoa  |
| Fergħa: | Bilateria  |
| Superphylum: | Deuterostomia  |
| Phylum: | **Chordata**  |
| Sottodiviżjoni: | Subphyla
* Tunicata/Urochordata
* Cephalochordata
* Vertebrata
 |

Il-**Kordati** (*Chordata*, Bateson 1885) jirrappreżentaw phylum ta' annimali li fih organiżmi ta' ħafna forom u komplessità, bħall-Vertebrati, l-Urokordati u ċ-Ċefalokordati. Dan il-phylum hu bbażat fuq struttura interna forma ta' bastun ta' support magħruf bħala *notokorda*.

L-Urokordati - jew Tunikati - huma oraniżmi żgħar tal-baħar, sessili u filtraturi, li jibdew bħala larvi planktoniċi li jeħlu ma' qiegħ il-baħar u meta jsiru adulti jiżviluppaw f'forma ta' borza miksija minn qoxra protettiva msejħa *tunika*. L-ascidiacea huma eżempju ta' dawn.

Iċ-Ċefalokordati, huma wkoll annimali tal-baħar, imma ġisimhom, twil minn 3 sa 5 ċm, għandu għamla tawwalija, bil-ponta fit-truf, qishom ħuta bir-ras mhux żviluppata. Huma għawwiema dagħjfa li jqattgħu l-parti l-kbira ta' ħajjithom iħaffru fir-ramel tal-kosti oċeaniċi, biex jindifnu u jieklu permezz tal-filtrazzjoni mill-parti ta' quddiem li jħallu barra r-ramel.

It-tielet grupp ta' Kordati hu rappreżentat mill-Kranjati, annimali li permezz ta' proċess ta' ċefalizzazzjoni żviluppaw ras distingwibbli sew mill-bqija tal-ġisem. Il-grupp tal-Kranjati fih il-missini (Myxini) ħajjin u s-subphylum tal-Vertebrati, organiżmi iżjed kumplessi li adattaw ruħhom għal kull tip ta' ambjent: ilma (il-ħut), arja (l-għasafar) u art (Anfibi, Rettili u Mammiferi).

## Morfoloġija

Minkejja li dawn it-tliet gruppi juru xi differenzi morfoloġiċi, meta nanalizzawhom iżjed bir-reqqa naraw li fir-realtà, huma iżjed qrib xulxin mill-punto di vista filoġenetiku. Infatti il-Kordati kollha b'simmetrija bilaterali, juru, almenu f'wieħed mill-fażijiet tal-iżvilupp tagħhom, xi *sinapomorfiji*, strutturi omoloġi ġejjin matul l-evoluzzjoni minn antenat wieħed komuni u juru l-parentela dritt minn għandu (takson monofiletiku).

Waħda minn dawn l-omolġiji, dik li tagħti l-isemm lill-phylum, hi l-korda dorsali jew in-*notokorda*. Din hi bastun f'nofs id-daħar magħmul minn materja elastika li fiha ċelluli għonja fil-glikoġenu. Jaġixxi ta' support u x'jiġri minnu matul l-iżvilupp ivarja skont il-grupp:

* Fl-*Uro*kordati hu preżenti biss fil-larva, fin-naħa tad-denb;
* Fiċ-*Ċefalo*kordati, qiegħed matul-ġisem u jibqa' matul ħajjithom;
* Fl-*Emiċefalo*kordati, l-embrijun għandu notokorda li testendi ma' tliet kwarti tal-ġisem barra r-ras. Fl-Agnatha (ħut bla xedaq) il-korda dorsali tibqa' hemm fl-istadju adult; fil-Gnathostomata, malajr jieħu posta l-iskeletru u ssir reġjun qasir ħafna wara d-Diencephalon;

Is-sistema nervuża tal-kordati tibda tieħu l-forma fuq id-dahar tal-korda fl-embrijun; l-ewwel tifforma, fuq id-denb, il-plakka newrali, li minnu jiżviluppa it-tubu newrali. Fil-vertebrati, fit-tarf oppost tat-tubu jifforma l-moħħ; fiċ-ċefalokordati, dan it-tarf isir ikbar biss. F'kull każ, in-nervi periferiċi jibdew mit-tubu newrali.

Fil-vertebrati, it-tubu newrali hu protett mill-vertebri, u l-moħħ hu protett mill-kranju. Is-segmenti tal-muskolu qegħdin wara xulxin u simmetrikament fil-ġnub tal-korda.

Tunikat tal-ġeneru *Halocynthia*
Fl-embrijun, it-tratt ta' wara tat-tubo diġerenti (li jissejjaħ ukoll il-farinġi brankjali) jikkomunika ma' barra permezz ta' xi fetħiet, li fil-każ tal-ħut jibqgħu hemm anki fl-istadju adult bħala garġi. Fil-kordati l-oħra matul l-iżvilupp jiġu sostitwiti mill-pulmun.

Fuq in-naħa ta' taħt tal-farinġi brankjali hemm radda msejħa d-doxxa brankjali. Din hi miksija bil-muku li jaġġixxi biex iżomm l-organiżmi mikroskopiċi ji jservu ta' ikel. Fil-vertebrati, id-doxxxa brankjali minflok, tinfired mit-tubu diġerenti biex tinbidel fit-tirojde.

Il-kordati kollha jixxibhu fil-fazi embrijonali u jesibixxu l-istess distribuzzjoni tal-organi (sistema nervuża, denb, aorta dorsali, tubu diġerenti u l-vaż tad-demm prinċipali, li hu il-qalb fil-każ tal-vertebrati). Fl-iżvilupp tal-embriju, il-morfoloġija tinbidel fl-ispeċi diversi.

## Klassifikazzjoni

### Tassonomija

Skeletru tal-baliena kaħla, l-ikbar annimal tad-dinja, barra l-*Long Marine Laboratory* tal-Università ta' California, Santa Cruz
Il-Bies, l-annimal l-iżjed veloċi fid-dinja
Tradizzjonalment Cephalochordata u Craniata kienu miġburin fil-klad "Euchordata", li kellu jkun il-grupp ħu Tunicata/Urochordata. Iżjed riċentement, Cephalochordata kien meqjus bħala grupp ħu "Olfactores", li jinkludi l-kranjati u t-tunikati. Il-kustjoni għadha mhijiex deċiża.

Din l-iskema ttieħdet mit-tielet edizzjoni ta' *Vertebrate Palaeontology*. Il-kordarti invertebrati huma meħuda minn *Fishes of the World*.

Waqt li hi mfassla biex tirrifletti r-relazzjonijiet evoluttivi (simili għal kladogramma), tirretieni fiha l-kategoriji tradizzjonali użati fit-tassonomija Linnejana.

* **Phylum Chordata**
	+ Subphylum **Tunicata** — (2150 speċi)
		- Klassi **Ascidiacea** (Aplousobranchia, Phlebobranchia, u Stolidobranchia)
		- Klassi **Thaliacea** (Pyrosomida, Doliolida, u Salpida)
		- Klassi **Appendicularia** (Larvacea)
		- Klassi **Sorberacea**
	+ Subphylum **Cephalochordata** — (30 speċi)
		- Klassi **Leptocardii**
	+ Subphylum **Vertebrata** (Craniata) (vertebrati — annimali bis-sinsla; 57,674 speċi)
		- Infraphylum incertae sedis
			* Superklassi '**Agnatha'** parafiletiċi (vertebrati bla xedaq; 100+ speċi)
				+ Klassi Myxini (65 speċi)
				+ Klassi Petromyzontida jewr Hyperoartia
				+ Klassi †Conodonta
				+ Klassi †Pteraspidomorphi
				+ Klassi †Thelodonti
				+ Klassi †Anaspida
				+ Klassi †Cephalaspidomorphi
		- Infraphylum **Gnathostomata** (vertebrati bix-xedaq)
			* Superklassi incertae sedis
				+ Klassi †**Placodermi** (forom Paleożojċi korazzati)
				+ Klassi **Chondrichthyes** (ħut kartilaġinej; 900+ speċi)
				+ Klassi †**Acanthodii** (Paleozoic "spiny sharks")
			* Superklassi **Osteichthyes** (ħut bil-għadam; 30,000+ speċi)
				+ Klassi **Actinopterygii** (ħut bil-ġwienaħ bir-raġġi; madwar 30,000 speċi)
				+ Klassi **Sarcopterygii** (ħut bil-ġwienaħ imlaħħmin: 8 speċi)
			* Superklassi **Tetrapoda** (vertebrati b'erba' membri; 28,000+ speċi)
				+ Klassi **Amphibia** (anfibi; 6,000 speċi)
				+ Klassi **Reptilia** (rettili; 9,000+ speċi)
				+ Klassi †**Synapsida** (sinapsidi; 4,000+ speċi)
				+ Klassi **Aves** (għasafar; 10,000-12,000 speċi, kważi 22,000 sottospeċi)
				+ Klassi **Mammalia** (mammiferi; 5,700+ speċi)

### Filoġenesi

|  |
| --- |
| Chordata |
|  |
| Kladogramma tal-phylum Chordata. Il-linji juru r-relazzjonijiet evoluttivi probabbli, inklużi t-taksa estinti li huma mmarkati bi stallett, †. Xi wħud minnhom huma invertebri. The positions (relationships) of the kladi Cephalochordata, Tunicata, u Craniata huma kif dehru fir-rivista xjentifika *Nature*.

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| **Chordata**  |

|  |  |  |  |  |
| --- | --- | --- | --- | --- |
| Cephalochordata |

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| --- | --- |
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Amphioxus |
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| **Olfactores** |

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| --- | --- |
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†*Haikouella* |
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| Tunicata |

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| --- | --- |
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Appendicularia (qabel Larvacea) |
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Thaliacea |
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Ascidiacea |
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| Craniata |

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Myxini |
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| Vertebrata |

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| --- | --- |
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†*Myllokunmingia fengjiaoa* |
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†*Zhongjianichthys rostratus* |
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Conodonta† |
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Cephalaspidomorphi† |
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Hyperoartia (Petromyzontida) |
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Pteraspidomorphi† |
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osteostracan |
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| --- | --- |
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Placodermi† (?parafiletiku) |
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Chondrichthyes |
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| Teleostomi |

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Acanthodii† (?parafiletiku) |
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| Osteichthyes |

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Actinopterygii |
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| Sarcopterygii |

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| void |

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  Tetrapoda  |

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| --- | --- |
|  |  Amphibia |
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|  Amniota  |

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| --- | --- |
|  |  Mammalia |
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|  Sauropsida  |

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| --- | --- | --- | --- | --- |
| void |

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| --- | --- |
|  |  Lepidosauromorpha (gremxul, sriep, tuwatari, u dawk l-annimali estinti li jiġu minnhom) |
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|  |  Archosauromorpha (kukkudrilli, għasafar, u dawk l-annimali estinti li jiġu minnhom) |
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## Referenzi

## Ħoloq esterni