楔形两极虫(黏体门,双壳目)的形态学重描述及其近缘种的分子系统学研究

Redescription of Myxidium cuneiforme Fujita,1924(Myxosporea: Bivalvulida) and Molecular Phylogeny with its Relative Species

两极虫属Myxidium和楚克拉虫属Zschokklella在形态上非常相似,形态鉴定界限模糊。为进一步厘清两者的分类学关系,本研究对采自涪江重庆市潼南县江段的楔形两极虫M.cuneiforme Fujita,1924进行了形态学重描述,并对其分子系统学进行了研究。楔形两极虫孢子壳面观呈长条形,中部稍凹陷或孢子一边突出,壳瓣上有6-8条与缝嵴平行的条纹;缝嵴直,缝面观呈梭形。孢子长12.5μm±0.3μm,宽5.4μm±0.3μm（n=20）。极囊2个,呈梨形,分布于孢子两极端;极囊长4.3μm±0.2μm,宽3.1μm±0.2μm（n=20）,极丝细长且明显,盘曲5-6圈。以18S rDNA为分子标记,对楔形两极虫及其近缘种进行了保守区变异、遗传距离、序列相似度和分子系统发育分析,结果表明：两极虫属和楚克拉虫属均非单系发生,两属间物种相互交叉聚支;两极虫属与楚克拉虫属物种间具有很近的亲缘关系。本文基于形态和分子数据的研究结果支持将两极虫属和楚克拉虫属合并为一个属的观点。

The species identification between Myxidium and Zschokklella is difficult due to their similar morphology and vague boundaries. To clarify the taxonomic relationship of the two genera,the morphology of Myxidium cuneiforme Fujita,1924 collected from the Fujiang River in Tongnan county,Chongqing,China was redescribed. Subsequently,molecular phylogeny was analyzed along with the relative species. The mature spore of M. cuneiforme was elongated in valvular view with the middle part concaved slightly. The surface of each valve had 6 - 8 longitudinal grooves. The suture line was straight,and spore was fusiform in sutural view. The spore was 12. 5 μm ± 0. 3 μm long and 5. 4 μm ± 0. 3 μm wide（ n = 20）,each with two polar capsules posited at the both end of the spore. The two polar capsules were pyriform with equal size of 4. 3 μm ± 0. 2 μm long and 3. 1 μm ± 0. 2 μm wide（ n = 20）,containing polar filaments coiled 5 - 6 turns.Analyses of the variation of conserved regions,genetic distances,sequence similarities and molecular phylogeny based on18 S rDNA sequences indicated that,Myxidium and Zschokkella were not monophyletic,as they clustered together with each other in the phylogenetic analysis. Therefore,Myxidium and Zschokkella had a very close genetic relationship. The results from the morphological and molecular data supported the proposal that Myxidium and Zschokkella should be assigned to one single genus.