# 無頜總綱[编辑]

| 無頜總綱化石时期：
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| 七鳃鳗
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| 科学分类 |
| 界： | 动物界 Animalia |
| 门： | 脊索动物门 Chordata |
| 演化支： | 嗅球類 Olfactores |
| 亚门： | 脊椎动物亚门 Vertebrata |
| 並系群： | 無頜總綱 Agnatha Cope, 1889 |
| 传统分类中包含的子类群
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| * 圓口綱 Cyclostomata
* †牙形石綱 Conodonta
* †昆明魚目 Myllokunmingiida
* †鰭甲魚綱 Pteraspidomorphi
* †花鱗魚綱 Thelodonti
* †缺甲魚綱 Anaspida
* †頭甲魚綱 Cephalaspidomorphi
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| 传统分类中未包含，但在 演化层面上包含的演化支
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| * 有頜總綱 Gnathostomata
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**无颌总纲** （學名：**Agnatha**）是脊索动物門下的一个总纲，包括现存的圆口纲（盲鳗和七鳃鳗）以及已灭绝的牙形石纲和各种甲胄鱼类（包括鳍甲鱼纲、花鳞鱼纲、缺甲鱼纲、盔甲鱼纲、茄甲鱼纲和骨甲鱼纲）。无颌纲动物是非常基群的脊椎动物，特点是口部没有颌骨，并且没有任何偶鳍，主要以滤食、寄生和食腐为生，有些种类会洄游。

## 特徵

大多數魚類的嘴具有鉸合的雙顎，但是無頜總綱的所有物種都沒有下頜。

間腦背面突出，有着結構類似眼睛的顱頂器。

## 演化

属于此总纲的动物演化历史已有五亿二千万多年，是迄今所知地层中最早出现的和最原始的脊椎动物。當中能存活至今的只剩圓口綱下的盲鰻亞綱和七鰓鰻亞綱。

海口魚的化石於云南的澄江动物群（帽天山层）被發現，溯源于寒武纪，被認為是至今发掘的最古老的鱼类。牠的發現對古生物學及動物源流的學說有極大的影響，因為牠把科學家原先預計脊椎動物出現的時期早推至5.2億年前。支序分類學研究顯示海口魚可能是最原始的無頜總綱。

豐嬌昆明魚是一種原始及可能屬於無頜總綱的魚類，生存於寒武紀的中國雲南澄江市帽天山。 是已知最古老的脊椎動物，在5億2千萬年前寒武紀的地層被發現。牠似乎是有由軟骨構造的頭顱骨及骨骼。牠的骨骼並未有出現生物礦化的跡象。

## 分類

目前的分類尚有爭議。

* †牙形石纲 Conodonta
* 圓口綱 Cyclostomata
	+ 七鰓鰻亞綱 Petromyzontida/Hyperoartia
	+ 盲鰻亞綱 Myxini
* †甲胄鱼类 Ostracodermi
	+ †鳍甲鱼纲 Pteraspidomorphi
		- †阿兰达鱼亚纲 Arandaspida
		- †异甲亚纲 Heterostracomorphi
	+ †花鳞鱼纲 Thelodonti
	+ †缺甲鱼纲 Anaspida
	+ †盔甲鱼纲 Galeaspida
	+ †茄甲鱼纲 Pituriaspida
	+ †骨甲鱼纲 Osteostraci
	+ 有頜类 Gnathostomata

## 系統發育學

以下支序圖基於 Mikko Haaramo和Delsuc et al等人的研究

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| 脊椎動物亞門/
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| 圓口綱
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盲鰻亞綱

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七鰓鰻亞綱

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?†牙形石綱

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†鰭甲魚綱

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| **肌鰭魚類 Myopterygii** |

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| 缺甲魚超綱 Anaspidomorphi
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?†莫氏魚目 Jamoytiiformes

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?†真顯魚目 Euphanerida

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†缺甲魚綱 Anaspida

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†花鱗魚綱 Thelodonti

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†盔甲魚綱 Galeaspida

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†茄甲魚綱 Pituriaspida

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†骨甲魚綱 Osteostraci

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有頜下門 Gnathostomata

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 | 頭甲魚綱 Cephalaspidomorphi
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| 有頭類
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以下支序圖基於Miyashita et al. 的研究，被認為符合生物形態學和分子生物學。

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†缺甲魚綱 Anaspida

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†*Pipiscius* |
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†真牙形石目 Euconodonta

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圓口總綱 Cyclostomi

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†鰭甲魚綱 Pteraspidomorphi

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†花鱗魚綱 Thelodonti

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†茄甲魚綱 Pituriaspida

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†盔甲魚綱 Galeaspida

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†骨甲魚綱 Osteostraci

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有頜下門 Gnathostomata

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†昆明魚科 Myllokunmingiidae

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* 豐嬌昆明魚:已知最古老的脊椎動物。
* 有頭動物 Craniata
* 头甲鱼纲 Cephalaspidomorphi

## 注釋