核形虫是一类原生生物，具有丝状伪足,生活在土壤和淡水里。它们与同样具有丝状伪足的vampyrellid形态上非常相似，但可以通过线粒体的盘状嵴来鉴别。

核形虫与动物、真菌以及其它一些小类群同属后鞭毛生物, 最近的研究显示核形虫是真菌的姊妹类群

The nucleariids are a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the superficially similar vampyrellids mainly by having mitochondria with discoid cristae.