Campos A, Cummings M P, Reyes J L, Laclette J P
Department of Immunology, Universidad Nacional Autónoma de México, D.F., México.
Mol Phylogenet Evol. 1998 Aug;10(1):1-10. doi: 10.1006/mpev.1997.0483.
Nucleotide sequences of 18S ribosomal RNA from 71 species of Platyhelminthes, the flatworms, were analyzed using maximum likelihood, and the resulting phylogenetic trees were compared with previous phylogenetic hypotheses. Analyses including 15 outgroup species belonging to eight other phyla show that Platyhelminthes are monophyletic with the exception of a sequence putatively from Acoela sp., Lecithoepitheliata, Polycladida, Tricladida, Trematoda (Aspidobothrii + Digenea), Monogenea, and Cestoda (Gyrocotylidea + Amphilinidea + Eucestoda) are monophyletic groups. Catenulids form the sister group to the rest of platyhelminths, whereas a complex clade formed by Acoela, Tricladida, "Dalyellioida", and perhaps "Typhloplanoida" is sister to Neodermata. "Typhloplanoida" does not appear to be monophyletic; Fecampiida does not appear to belong within "Dalyellioida," nor Kalyptorhynchia within "Typhloplanoida." Trematoda is the sister group to the rest of Neodermata, and Monogenea is sister group to Cestoda. Within Trematoda, Aspidobothrii is the sister group of Digenea and Heronimidae is the most basal family in Digenea. Our trees support the hypothesis that parasitism evolved at least twice in Platyhelminthes, once in the ancestor to Neodermata and again in the ancestor of Fecampiida, independently to the ancestor of putatively parasitic "Dalyellioida."
利用最大似然法分析了71种扁形动物（即扁虫）的18S核糖体RNA的核苷酸序列，并将所得的系统发育树与先前的系统发育假说进行了比较。包括属于其他八个门的15个外类群物种的分析表明，扁形动物是单系的，但有一个序列可能来自无肠目物种、卵黄上皮纲、多肠目、三肠目、吸虫纲（盾腹亚纲+复殖亚纲）、单殖纲和绦虫纲（旋缘绦虫目+双线绦虫目+真绦虫目）除外，它们是单系群。链涡虫纲是其余扁形动物的姐妹群，而由无肠目、三肠目、“达氏涡虫目”以及可能的“盲涡虫目”组成的复杂分支是新皮动物的姐妹群。“盲涡虫目”似乎不是单系的；费坎皮目似乎不属于“达氏涡虫目”，卡利普托吻目也不属于“盲涡虫目”。吸虫纲是其余新皮动物的姐妹群，单殖纲是绦虫纲的姐妹群。在吸虫纲中，盾腹亚纲是复殖亚纲的姐妹群，赫罗尼米科是复殖亚纲中最基部的科。我们的系统发育树支持这样的假说，即寄生在扁形动物中至少独立进化了两次，一次在新皮动物的祖先中，另一次在费坎皮目的祖先中，与假定寄生的“达氏涡虫目”的祖先无关。
