# 後口動物[编辑]

| 後口動物總門 化石时期：寒武纪－現代
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| --- |
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| 科学分类  |
| 界： | 动物界 Animalia |
| 演化支： | 副同源异形基因动物 ParaHoxozoa |
| 演化支： | 两侧对称动物 Bilateria |
| 演化支： | 腎管動物 Nephrozoa |
| 总门： | **後口動物總門 Deuterostomia** Grobben, 1908 |
| 門
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| * ?†皺囊蟲屬 *Saccorhytus*
* ?†古蟲動物門 Vetulicolia
* 脊索動物門 Chordata
* 步带动物 Ambulacraria
	+ 半索動物門 Hemichordata
	+ 棘皮動物門 Echinodermata
	+ †寒武枝觸動物 Cambroernida
 |

**後口動物總門**（学名：Deuterostomia）是動物界真後生動物亞界兩側對稱動物下界的一個總門，在生物分类学中和原口動物同属肾管动物这一演化支。後口動物和原口動物的主要区别在于胚胎發育时消化道开孔的形成顺序：在後口動物中，第一個形成的開口（胚孔）變成了肛門，而在原口動物中則變成了嘴巴。

後口動物之下共有三個現存的門：

* 脊索動物門（Chordata）
	+ 脊椎动物亚门——所有的鱼类、两栖类、爬行类、鸟类和哺乳类
	+ 头索动物——文昌鱼、偏文昌鱼以及灭绝的皮卡虫
	+ 被囊动物——海鞘、樽海鞘、尾海鞘及其同类
* 棘皮動物門（Echinodermata）
	+ 海星亚门——海星和蛇尾
	+ 海胆亚门——海膽和海參
	+ 海百合亚门——海百合以及以灭绝的海蕾、海座星等
* 半索動物門（Hemichordata）——柱頭蟲、玉钩虫以及羽鳃纲的头盘虫、无管虫等，已灭绝的筆石可能也是

已滅絕的類群還包括已知最早的後口動物皺囊蟲屬（*Saccorhytus*），以及生存年代稍晚的古蟲動物門（Vetulicolia），但也有學者將該門劃分為脊索動物門之下的一個亞門。

後口動物和前口動物，其受精卵一開始都會發育成一個由細胞組成的小球，稱之為囊胚。在後口動物中，初期的部份會平行或垂直極軸，這稱為輻射卵割，也會出現在某些原口動物上，如觸手冠動物。大多數的後口動物會行不定卵割，其細胞在胚胎中的發展不是由母細胞來決定的。因此，若將一開始的四個細胞分開，每一個細胞都能夠形成一個完整的幼體，且若一個細胞被移出了囊胚，其他的細胞就會補充進來。

半索動物和脊索動物都有鰓裂，且原始化石中的棘皮動物也顯示出有鰓裂的記號。在所有脊索動物，包括尾索動物（在幼體的階段）之中，都有著中空的神經索。一些的半索動物也會有管狀的神經索，在胚胎早期時看起來像是脊索動物的中空神經索。因為棘皮動物那退化的神經系統，分辨其祖先是否也是如此是不可能的，但依其他不同的事實來看，有相當的可能性，所有現存的後口動物都演化自一個有腮裂、中空神經索和分段的身體。此一祖先應類似寒武紀時被稱做古蟲動物的小後口動物類群。

## 演化树

以下为与**后口动物**（及姐妹群原口动物）相关的支序演化树示意图。 演化支出现距今的年代以百万年为单位（Mya）记。

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| 肾管动物 Nephrozoa
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| **后口动物 Deuterostomia** |

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| 脊索动物门 Chordata
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头索动物亚门 Cephalochordata  |
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| 嗅球类 Olfactores
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被囊动物亚门/尾索动物亚门 Tunicata/Urochordata  |
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脊椎动物亚门/有头类 Vertebrata/Craniata  |
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| 步带动物 Ambulacraria
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| 棘皮动物门 Echinodermata
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海百合亚门 Crinoidea |
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| 海星亚门 Asterozoa
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海星纲 Asteroidea  |
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蛇尾纲 Ophiuroidea  |
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| 海胆亚门 Echinozoa
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海胆纲 Echinoidea  |
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海参纲 Holothuroidea  |
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| 半索动物门 Hemichordata
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| 羽鳃纲 Pterobranchia
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头盘虫科 Cephalodiscidae  |
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Rhabdopleuridae  |
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| 肠鳃纲 Enteropneusta
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玉钩虫科 Harrimaniidae

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无翼柱头虫科 Spengelidae

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| Ptychoderidae
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Torquaratoridae

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| 526 mya
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| 原口动物 Protostomia
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| 蛻皮动物 Ecdysozoa
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| Scalidophora
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鳃曳动物门 Priapulida  |
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动吻动物门 Kinorhyncha  |
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| 线虫动物 Nematoida
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线虫动物门 Nematoda  |
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线形虫动物门 Nematomorpha  |
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铠甲动物门 Loricifera  |
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| 泛节肢动物 Panarthropoda
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有爪动物门 Onychophora  |
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| 序足动物 Tactopoda
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缓步动物门 Tardigrada  |
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节肢动物门 Arthropoda  |
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| >529 mya
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| 螺旋动物 Spiralia  |

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|  | 有顎動物  |
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| 扁蟲冠輪動物 (580)
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| 中生动物 Mesozoa
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菱形动物门 Dicyemida

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直泳动物门 Orthonectida

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单胚动物门 Monoblastozoa

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| 吮食動物 Rouphozoa
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腹毛动物门 Gastrotricha

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扁形动物门 Platyhelminthes  |
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| 冠輪動物 Lophotrochozoa
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環口動物門 Cycliophora

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环节动物门 Annelida  |
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软体动物门Mollusca  |
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| 隐担轮动物 |

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| 觸手冠動物 Lophophorata
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| 腕動物 Brachiozoa
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腕足動物門 Brachiopoda

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帚虫动物门 Phoronida

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| 苔藓动物 Bryozoa
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内肛动物门 Entoprocta

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外肛动物门 Ectoprocta

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纽形动物门 Nemertina

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|  | †金伯拉虫 Kimberella (555 mya)  |
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| 550 mya
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| 575 mya
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## 参考资料

* 生命演化歷程

* UCMP-Deuterostomes