Irie Naoki, Satoh Noriyuki, Kuratani Shigeru
1Department of Biological Sciences, School of Science, University of Tokyo, Tokyo, 113-0033 Japan.
2Universal Biology Institute, University of Tokyo, Tokyo, 113-0033 Japan.
Zoological Lett. 2018 Dec 26;4:32. doi: 10.1186/s40851-018-0114-y. eCollection 2018.
The group Vertebrata is currently placed as a subphylum in the phylum Chordata, together with two other subphyla, Cephalochordata (lancelets) and Urochordata (ascidians). The past three decades, have seen extraordinary advances in zoological taxonomy and the time is now ripe for reassessing whether the subphylum position is truly appropriate for vertebrates, particularly in light of recent advances in molecular phylogeny, comparative genomics, and evolutionary developmental biology. Four lines of current research are discussed here. First, molecular phylogeny has demonstrated that Deuterostomia comprises Ambulacraria (Echinodermata and Hemichordata) and Chordata (Cephalochordata, Urochordata, and Vertebrata), each clade being recognized as a mutually comparable phylum. Second, comparative genomic studies show that vertebrates alone have experienced two rounds of whole-genome duplication, which makes the composition of their gene family unique. Third, comparative gene-expression profiling of vertebrate embryos favors an hourglass pattern of development, the most conserved stage of which is recognized as a phylotypic period characterized by the establishment of a body plan definitively associated with a phylum. This mid-embryonic conservation is supported robustly in vertebrates, but only weakly in chordates. Fourth, certain complex patterns of body plan formation (especially of the head, pharynx, and somites) are recognized throughout the vertebrates, but not in any other animal groups. For these reasons, we suggest that it is more appropriate to recognize vertebrates as an independent phylum, not as a subphylum of the phylum Chordata.
脊椎动物门目前被列为脊索动物门下的一个亚门，与另外两个亚门，即头索动物亚门（文昌鱼）和尾索动物亚门（海鞘）同属脊索动物门。在过去三十年里，动物分类学取得了非凡进展，现在是重新评估脊椎动物的亚门地位是否真正合适的时候了，特别是鉴于分子系统发育学、比较基因组学和进化发育生物学的最新进展。本文讨论了当前四条研究线索。第一，分子系统发育学表明，后口动物包括步带动物（棘皮动物和半索动物）和脊索动物（头索动物亚门、尾索动物亚门和脊椎动物门），每个进化枝都被视为相互可比的门。第二，比较基因组研究表明，只有脊椎动物经历了两轮全基因组复制，这使得它们的基因家族组成独一无二。第三，脊椎动物胚胎的比较基因表达谱显示出一种沙漏状的发育模式，其中最保守的阶段被认为是一个系统发育阶段，其特征是确立了与一个门明确相关的身体结构。这种胚胎中期的保守性在脊椎动物中得到了有力支持，但在脊索动物中支持较弱。第四，在整个脊椎动物中都能识别出某些复杂的身体结构形成模式（特别是头部、咽部和体节的模式），但在任何其他动物类群中都没有。基于这些原因，我们认为将脊椎动物视为一个独立的门，而不是脊索动物门下的一个亚门更为合适。
