Order Anostraca (fairy shrimp of large branchiopods) is a primitive crustacean group, retaining ancient forms and ecology. The Holarctic family Chirocephalidae originated over 100 million years ago; it is a very long-lived freshwater taxon that has survived from the Mesozoic to the present. Thus, using this taxon as an indicator, we verified how the geographical distribution of freshwaters shifted during the ancient era. We used newly collected samples of Drepanosurus uchidai from Aomori (northern Japan) and Galaziella baikalensis and Branchinecta orientalis from Olkhon Island (the largest lake-bound island of Lake Baikal, Russia) to sequence 658 bp of COI gene. These sequences, plus those of 16S rRNA gene (~ 550-bp mt16S rDNA fragment), were compared with those retrieved from GenBank. To re-evaluate and clarify phylogenetic relationships among the Chirocephalidae that remains confused till now, six genera of the family, including Polyartemiella, Drepanosurus, Eubranchipus, Chirocephalus, Artemiopsis, and Galaziella species were used for molecular analyses. Small water bodies usually have comparatively short lives and fade away sooner or later due to growth of aquatic plants and accumulation of bottom sediments. In such environments, refugia formed on the shores of large-scale lakes were necessary for large branchiopods to survive several Ice Ages. The lake shorelines have moved with the growth or decline of the lakes, but the habitats of large branchiopods sporadically left behind can now be confirmed as a history of the shifting geographical distribution of global freshwaters. For example, two types of large branchiopod populations from island-bound water bodies on Olkhon Island are recognized: (1) populations on the northwestern coast that are closely related to the group in the Mongolian Gobi steppe region, and (2) populations in other areas distant from the coast that are highly endemic to the island. Based on fossil records and genetic distances, an absolute differentiation time of world chirocephalids can be estimated as 140 million years ago in the Mesozoic era. On the other hand, the age of Lake Baikal is only 25‒30 million years at the most. Therefore, extant large branchiopods of Olkhon Island must have first appeared near the present lake catchment after separation from their ancestral populations that had originated in Europe, and before the formation of Lake Baikal.

中文翻译：

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神仙虾（Branchiopoda，Anostraca）的散发是否反映了自中生代晚期以来淡水地理分布的变化？

Order Anostraca（大型支足类动物的仙女虾）是原始的甲壳类动物，保留着古老的形态和生态。幽灵家族手足目科起源于一亿多年前。从中生代到现在，这是一个非常长寿的淡水生物。因此，使用该分类单元作为指标，我们验证了古代时期淡水的地理分布是如何变化的。我们使用了新采集的来自青森县（日本北部）的Drepanosurus uchidai样本以及Balkaalensis和Galaziella baikalensis和Berlininecta Orientalis从Olkhon岛（俄罗斯贝加尔湖最大的湖岸岛）到COI基因658 bp序列。这些序列，加上16S rRNA基因的序列（〜550 bp mt16S rDNA片段），与从GenBank检索到的序列进行了比较。重新评估和澄清Chirocephalidae之间亲缘关系剩下的困惑至今，六个属家族，包括Polyartemiella，Drepanosurus，Eubranchipus，丰年虫，Artemiopsis和Galaziella物种用于分子分析。小型水体的寿命通常较短，并且由于水生植物的生长和底部沉积物的积累而早晚消失。在这样的环境中，大型湖泊的岸上形成的避难所对于大型支足类动物生存几个冰河时期是必需的。湖泊的海岸线随着湖泊的增长或下降而移动，但是现在可以将零星留在的大型支脚类动物的栖息地确定为全球淡水地理分布变化的历史。例如，从奥尔洪岛的岛上水体中识别出两种类型的大型叉足类种群：（1）与蒙古戈壁草原地区的种群密切相关的西北海岸种群，（2）远离海岸的其他地区的岛屿上高度流行的人口。根据化石记录和遗传距离，世界中手足类动物的绝对分化时间可以估计在中生代的1.4亿年前。另一方面，贝加尔湖的年龄最多只有25‒3000万年。因此，奥尔洪岛的现存大型支足类动物一定是在与欧洲起源的祖先种群分离之后，并在贝加尔湖形成之前，首先出现在当前的湖泊集水区附近。贝加尔湖的年龄最多只有25‒3000万年。因此，奥尔洪岛的现存大型支足类动物一定是在与欧洲起源的祖先种群分离之后并在贝加尔湖形成之前首先出现在当前的湖泊集水区附近。贝加尔湖的年龄最多只有25‒3000万年。因此，奥尔洪岛的现存大型支足类动物一定是在与欧洲起源的祖先种群分离之后并在贝加尔湖形成之前首先出现在当前的湖泊集水区附近。