Several evolutionary lineages of Amoebozoa are characterized by unusual morphological and ultrastructural features that impede resolving of their position in the phylogenetic tree. Among them is the genus Stygamoeba, not yet reliably placed on the phylogenetic tree even by a phylogenomic analysis. Only two species of Stygamoeba are known at present, and molecular data exists on one species only. Here, we present a description of the mesohaline species Stygamoeba cauta n. sp. isolated from the bottom sediments of Nivå Bay (Baltic Sea, The Sound). This stick-like, flattened amoeba morphologically resembles the previously described species Stygamoeba regulata Smirnov, 1996. However, the molecular analysis based on the 18S rRNA gene sequences and differences in cell behavior and pattern of locomotion provide strong support for establishing a new species.

变形虫的几个进化世系的特征是异常的形态和超微结构特征，阻碍了它们在系统树中的位置解析。其中有Stygamoeba属，即使通过种系分析仍不能可靠地置于系统发育树上。目前仅知道香蒲属的两个物种，并且分子数据仅存在于一个物种中。在这里，我们介绍了中盐类物种Stygamoeba cauta n。sp。与Nivå湾（波罗的海，海峡）的底部沉积物隔离。这种棍状扁平的变形虫在形态上类似于先前描述的Stygamoeba regulata Smirnov，1996年。但是，基于18S rRNA基因序列的分子分析以及细胞行为和运动模式的差异为建立新物种提供了有力的支持。