Huber J L, da Silva K B, Bates W R, Swalla B J
Biology Department, Institute for Molecular Evolutionary Genetics, Pennsylvania State University, University Park, PA 16802, USA.
Semin Cell Dev Biol. 2000 Dec;11(6):419-26. doi: 10.1006/scdb.2000.0195.
Ascidians are urochordates, marine invertebrates with non-feeding motile chordate tadpole larvae, except in the family Molgulidae. Urodele, or tailed, Molgulids have typical ascidian chordate tadpole larvae possessing tails with muscle cells, a notochord, and a dorsal hollow nerve cord. In contrast, anural (or tail-less) Molgulids lack a tail and defining chordate features. Molecular phylogenies generated with 18S and 28S ribosomal sequences indicate that Molgulid species fall into at least four distinct clades, three of which have multiple anural members. This refined and expanded phylogeny allows careful examination of the factors that may have influenced the evolution of tail-less ascidians.
海鞘是尾索动物，属于海洋无脊椎动物，除了莫氏海鞘科外，其具有不摄食的能动的脊索动物蝌蚪幼虫。有尾的蝾螈类莫氏海鞘具有典型的海鞘脊索动物蝌蚪幼虫，其尾巴有肌肉细胞、一条脊索和一条背侧中空神经索。相比之下，无尾的莫氏海鞘没有尾巴，也没有典型的脊索动物特征。利用18S和28S核糖体序列生成的分子系统发育树表明，莫氏海鞘物种至少分为四个不同的进化枝，其中三个进化枝有多个无尾成员。这种经过细化和扩展的系统发育树有助于仔细研究可能影响无尾海鞘进化的因素。
