刺胞動物門
刺胞動物門（學名：Cnidaria；/naɪˈdɛəriə/[5]），又名刺絲胞動物門，是一個包含有超過2萬多個动物物种的门 [6]，皆為生活於水中（包括淡、海水或其他鹹水棲境），不過絕大多數物種均棲息於海洋。Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of 中胶层, a non-living jelly-like substance, sandwiched between two layers of 上皮組織 that are mostly one 细胞 thick. They have two basic body forms: swimming 水母e and sessile polyps, both of which are radially symmetrical with mouths surrounded by 觸手 that bear cnidocytes. Both forms have a single orifice and body cavity that are used for 消化作用 and 呼吸 (生理學). Many cnidarian species produce colonies that are single organisms composed of 美杜莎-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized 神经 net and simple receptors. Several free-swimming species of 立方水母纲 and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians 有性生殖, with many species having complex life cycles of 无性生殖 polyp stages and sexual medusae. Some, however, omit either the polyp or the medusa stage.
刺胞動物門 化石时期：
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| Pacific sea nettles, Chrysaora fuscescens | |
科学分类 
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| 界： | 动物界 Animalia |
| 亚界： | 真後生動物亞界 Eumetazoa |
| 演化支： | 副同源异形基因动物 ParaHoxozoa |
| 门： | 刺胞動物門 Cnidaria Hatschek, 1888 |
| Subphyla[4] and classes | |
刺胞動物曾經和櫛水母動物一起組成腔腸動物門，但隨着對這兩種動物的差異的認識，愈來愈多學者同意應該將櫛水母動物從刺胞動物獨立出來。 刺胞動物可大致娓為四個群組：the almost wholly sessile 珊瑚纲 (海葵s, 珊瑚s, 海鳃s); swimming Scyphozoa (jellyfish); 立方水母纲 (box jellies); and Hydrozoa, a diverse group that includes all the freshwater cnidarians as well as many marine forms, and has both sessile members, such as Hydra, and colonial swimmers, such as the 僧帽水母. Staurozoa have recently been recognised as a 纲 in their own right rather than a sub-group of Scyphozoa, and the parasitic 黏體動物 and Polypodiozoa were only firmly recognized as cnidarians in 2007.[7]
Most cnidarians prey on 生物 ranging in size from 浮游生物 to animals several times larger than themselves, but many obtain much of their nutrition from 双鞭毛虫门s, and a few are 寄生. Many are preyed on by other animals including 海星, 裸鰓類, 鱼, 龜s, and even other cnidarians. Many 石珊瑚目n corals—which form the structural foundation for 珊瑚礁s—possess polyps that are filled with symbiotic photo-synthetic 蟲黃藻. While reef-forming corals are almost entirely restricted to warm and shallow marine waters, other cnidarians can be found at great depths, in 極地s, and in freshwater.
近期的系统发生学分析支持刺胞動物是一個单系群，而且與两侧对称动物是旁系群關係[8]。在大約5.8億年前形成的岩石中發現了刺胞動物的化石，其他化石表明珊瑚可能在4.9億年前左右才出現，並在幾百萬年後出現多樣化。然而，線粒體基因的molecular clock分析表明，crown group的年齡要大得多，估計大約有7.41億年前，在寒武紀以至任何化石出現的時期還要早2億年[9]。
注釋
參考文獻
- ^ Subphylum Medusozoa. ITIS. [2018-03-18].
- ^ 2.0 2.1 Maruques & Collins (2004)
- ^ 引用错误：没有为名为
Collins2002PhylogenyOfMedusozoa的参考文献提供内容 - ^ Subphyla Anthozoa and Medusozoa based on The Taxonomicon – Taxon: Phylum Cnidaria. Universal Taxonomic Services. [2007-07-10]. （原始内容存档于2007-09-29）.
- ^ Dictionary.com Unabridged. Random House, Inc. Cnidaria. Retrieved May 15, 2013.
- ^ Zhang, Z.-Q. Animal biodiversity: An introduction to higher-level classification and taxonomic richness (PDF). Zootaxa. 2011, 3148: 7–12.
- ^ E. Jímenez-Guri; et al. Buddenbrockia is a cnidarian worm. Science. July 2007, 317 (116): 116–118. Bibcode:2007Sci...317..116J. PMID 17615357. doi:10.1126/science.1142024.
- ^ Zapata F, Goetz FE, Smith SA, Howison M, Siebert S, Church SH, et al. Phylogenomic Analyses Support Traditional Relationships within Cnidaria.. PLOS ONE. 2015, 10 (10): e0139068. Bibcode:2015PLoSO..1039068Z. PMC 4605497
. PMID 26465609. doi:10.1371/journal.pone.0139068.
- ^ Park E, Hwang D, Lee J, Song J, Seo T, Won Y. Estimation of divergence times in cnidarian evolution based on mitochondrial protein-coding genes and the fossil record.. Molecular Phylogenetics & Evolution. 2012-01, 62 (1): 329–45. PMID 22040765. doi:10.1016/j.ympev.2011.10.008.
