The morphology, ontogenesis, conjugation, and phylogenetic position of Metopus boletus nov. spec. were studied using live observation, various silver impregnation methods, scanning electron microscopy, morphometry, and the 18S rRNA gene sequence. The new species is outstanding in having a mushroom-like appearance; a globular to broadly ellipsoid macronucleus in anterior body half; 5–10 elongated caudal cilia; 4–6 dikinetids curved rightwards in the anterior portion of the first postoral kinety; and an adoral zone composed of an average of 28 small polykinetids. Ontogenesis of M. boletus follows the metopid mode and the species-specific vegetative morphology is obtained after division. Its conjugation is temporary, isogamic and the partners unite ventral-to-dorsal, forming strongly arched to almost rod-like pairs, which indicates a heteropolar arrangement. There are only two maturation divisions and a single synkaryon division in exconjugants. The conjugation data corroborate a sister group relationship of the classes Armophorea and Litostomatea within the SAL (Spirotrichea + Armophorea + Litostomatea) supercluster in that the partners unite ventral-to-dorsal and the main body axes are antiparallel. On the other hand, the last common ancestor of the spirotricheans very likely had a ventral-to-ventral and homopolar conjugation mode with the main body axes oriented in parallel.

牛肝菌的形态，形成，结合及系统发生位置。规格 使用实时观察，各种银浸渍方法，扫描电子显微镜，形态学和18S rRNA基因序列进行了研究。该新物种具有蘑菇状的外观。前半部球状至宽椭圆形的大核；尾纤毛5–10；第一个口腔运动的前部向右弯曲4–6个双歧动物；以及一个由平均28个小的多动骨动物组成的上颚区域。个体发育的M.牛肝菌遵循类似类动物模式，分裂后获得特定物种的营养形态。它的共轭是暂时的，是等距的，并且伙伴团结腹侧到背侧，形成坚固的弓形，几乎成棒状，这表明是异极性的排列。exonjugant中只有两个成熟部门和一个synkaryon部门。共轭数据证实了SAL（Spirotrichea + Armophorea + Litostomatea）超级集群中的Armophorea和Litostomatea类的姐妹组关系，因为伙伴将腹对背和主体轴反平行。另一方面，螺旋藻的最后一个共同祖先很可能具有腹-腹-同极性共轭模式，其主体轴平行。