Isodiametridae is a large family of Acoela with 22 nominal genera and nearly 100 species. Unfortunately, systematics of Isodiametridae, as it stands, is highly problematic. Genera frequently have been proposed without reference to an explicit phylogenetic hypothesis, such that the current classification system holds little or no predictive power. Many taxa do not fit with the family diagnosis, and it is increasingly difficult to determine in which taxon a new species should be described. Herein, we reconstruct the phylogenetic relationships of Acoela with a focus on Isodiametridae using both previously published and new ribosomal and mitochondrial sequence data. Our dataset comprises sequences from 45 species representing 16 of the 22 isodiametrid genera. Our results recovered a well-supported Isodiametridae, but provided further evidence that the family and several genera within require revision. We have updated the classification system of Isodiametridae to be consistent with its phylogeny, including the transference of Otocelis to Otocelididae, Postaphanostoma and Faerlea to Mecynostomidae and Alluna to Actinoposthiidae. Six other genera are placed in synonymy. We review the morphological taxonomy and provide an identification key of the genera in the revised family.

中文翻译：

---

Acoel家族Isodiametridae的系统发育评估和系统修订

Isodiametridae 是 Acoela 的一个大科，有 22 个名义属和近 100 个物种。不幸的是，Isodiametridae 的系统学，就目前而言，是非常成问题的。经常在没有参考明确的系统发育假设的情况下提出属，因此当前的分类系统几乎没有或没有预测能力。许多分类群不符合科诊断，并且越来越难以确定应该在哪个分类单元中描述一个新物种。在这里，我们使用以前发表的和新的核糖体和线粒体序列数据重建了 Acoela 的系统发育关系，重点是 Isodiametridae。我们的数据集包含来自 45 个物种的序列，代表 22 个等径属中的 16 个。我们的结果恢复了一个得到良好支持的等径科，但提供了进一步的证据表明该科和其中的几个属需要修订。我们更新了 Isodiametridae 的分类系统以与其系统发育保持一致，包括 Otocelis 到 Otocelididae 的转移，Postaphanostoma 和 Faerlea 到 Mecynostomidae 和 Alluna 到 Actinoposthiidae 的转移。其他六个属放在同义词中。我们回顾了形态分类学，并提供了修订科中属的识别键。