Daly Marymegan, Lipscomb Diana L, Allard Marc W
Department of Biological Sciences, The George Washington University, Washington, DC 20052, USA.
Evolution. 2002 Mar;56(3):502-10. doi: 10.1111/j.0014-3820.2002.tb01361.x.
Many members of the cnidarian subclass Zoantharia (sea anemones, corals, and their allies) pass through a larval stage with eight complete mesenteries and without posterior musculature. This larva is usually transient, developing into an adult with 12 or more mesenteries. The adults of one family of sea anemones, the Edwardsiidae, bear the larval number and arrangement of mesenteries and lack the pedal disc seen in other sea anemones. The morphology of the Edwardsiidae has been interpreted in a number of ways: (1) the Edwardsiidae are the most basal extant zoantharian, having diverged before the evolution of additional mesenteries and basal musculature; (2) they are relatively advanced sea anemones that have secondarily simplified because they burrow in sand or mud rather than attaching to a hard substrate; or (3) edwardsiids are derived anemones that have retained a juvenile morphology through paedomorphosis. Phylogenetic analyses of small subunit ribosomal gene sequences reveal that the Edwardsiidae are derived zoantharians, nested within sea anemones. None of the proposed explanations fully explain the edwardsiid's body plan; edwardsiid anatomy is a mosaic of retained primitive and derived features. The results of the present study provide insight into zoantharian phylogeny and illustrate how phylogenetic tests can be used to study the evolution of cnidarian body plans.
刺胞亚纲六放珊瑚亚纲（海葵、珊瑚及其同类）的许多成员都要经历一个幼虫阶段，该阶段有八个完整的隔膜且没有后部肌肉组织。这种幼虫通常是过渡性的，会发育成具有12个或更多隔膜的成体。海葵中的一个科——艾氏海葵科的成体保留了幼虫期隔膜的数量和排列方式，并且没有其他海葵所具有的基盘。对于艾氏海葵科的形态学有多种解释：（1）艾氏海葵科是现存最原始的六放珊瑚亚纲动物，在额外隔膜和基部肌肉组织进化之前就已经分化；（2）它们是相对高等的海葵，由于它们在沙子或泥中挖掘而不是附着在坚硬的基质上，所以次生简化了；或者（3）艾氏海葵是衍生的海葵，通过幼态持续保留了幼年形态。对小亚基核糖体基因序列的系统发育分析表明，艾氏海葵科是衍生的六放珊瑚亚纲动物，嵌套在海葵之中。没有一种提出的解释能完全解释艾氏海葵科的身体结构；艾氏海葵科的解剖结构是保留的原始特征和衍生特征的混合体。本研究结果为六放珊瑚亚纲的系统发育提供了见解，并说明了如何利用系统发育测试来研究刺胞动物身体结构的进化。
