Abstract：
Karyorelictids are a group of ciliates inhabiting marine and freshwater biotopes and possessing a non-dividing macronucleus. We describe a new freshwater species based on morphology and the 18S rRNA gene sequence data. Loxodes tziscaensis n. sp. can be easily distinguished from other Loxodes species by the arrangement of the nuclear apparatus and features of the buccal and somatic ciliature. The current proposed 18S rRNA phylogeny of Loxodes, including seven Loxodes species, shows two morphologically well-supported groups. Group A (L. rostrum, type species; L. vorax and L. tziscaensis n. sp.) includes species with a single nuclear group (two macronuclei and one micronucleus), in contrast to species of group B, which possess more than one nuclear group (L. striatus, L. magnus, L. kahli, L. penardi, and L. rex). We propose that the last common ancestor of Loxodes was a marine Remanella-like species possessing a single nuclear group. The division and differentiation of the micronucleus into a new macronucleus and the retention of the old macronuclei, independently of cell division, may have been two crucial processes during the evolution and diversification of Loxodes species with one nuclear group into species with multiple nuclear groups.
摘要：
核纤毛虫是一群纤毛虫，居住在海洋和淡水生物群落中，具有不分裂的大核。我们根据形态学和18SrRNA基因序列数据描述了一种新的淡水物种。ziscaensisn.sp.通过核装置的布置以及颊和躯体纤毛的特征，可以很容易地将其与其他Loxodes物种区分开。当前提出的Loxodes的18SrRNA系统发育，包括七个Loxodes物种，显示了两个形态支持良好的组。A组(L.讲台,类型种；沃拉落叶松和齐斯卡落叶松。）包括具有单个核组（两个大核和一个微核）的物种，与B组的物种相比，拥有一个以上的核基团(L.纹状体,L.马格努斯,L.kahli,L.penardi,和L.雷克斯）。我们认为Loxodes的最后一个共同祖先是具有单个核群的海洋Remanella样物种。将微核分裂分化为新的大核，并保留旧大核，独立于细胞分裂，在将具有一个核基团的Loxodes物种进化和多样化为具有多个核基团的物种的过程中，可能是两个关键过程。
