Arcellinida (lobose testate amoebae) are abundant and diverse in many ecosystems, especially in moist to aquatic environments. Molecular phylogeny has shown that overall test morphology (e.g., spherical or elongate) is generally conserved in Arcellinida lineages, but the taxonomic value of other traits (e.g., size, ornamentation, mixotrophy/heterotrophy metabolism type) has not been systematically evaluated. Morphological and physiological traits that correspond to genetic differences likely represent adaptive traits of ecological significance. We combined high-resolution phylogenetics (NAD9-NAD7 genes) and advanced morphometrics to assess the phylogenetic signal of morphological traits of a group of elongate Difflugia species (Arcellinida). The phylogenetic analyses revealed two clades which could be reliably separated by test size and the presence/absence of mixotrophy. Differences in test size may reflect trophic level, with smaller organisms occupying lower trophic levels. In addition to having larger tests, elongate mixotrophic Difflugia are characterised by wide, flat bases and an inflation of the lower two thirds of their test. These morphological traits may provide additional volume for endosymbionts and/or increased surface area to aid light transmission. Our results showcase greater diversity within the elongate Difflugia and highlight morphological traits of ecological and evolutionary significance.

在许多生态系统中，尤其是在潮湿到水生环境中，Arcellinida（疏松的睾丸变形虫）丰富多样。分子系统学研究表明，总体测试形态（例如球形或细长形）在Arcellinida谱系中通常是保守的，但尚未对其他特征（例如大小，装饰，混合营养/异养代谢类型）的分类学价值进行评估。与遗传差异相对应的形态和生理特征可能代表具有生态学意义的适应性特征。我们结合高分辨率系统发育学（NAD9-NAD7基因）和先进的形态计量学，以评估一组细长的溢流的形态特征的系统发生信号种（Arcellinida）。系统发育分析表明，可以通过测试大小和是否存在混合营养来可靠地分离出两个进化枝。测试大小的差异可能反映了营养水平，较小的生物体则占据了较低的营养水平。除了进行更大的测试外，细长的混合营养型溢流症的特征还在于宽而平坦的基部和膨胀率低至三分之二的测试。这些形态特征可以为共生内膜提供额外的体积和/或增加表面积以帮助透光。我们的研究结果显示了拉长的溢流中更大的多样性，并突出了具有生态学和进化意义的形态特征。