有孔虫界（Rhizaria）为原生生物的一条主线。它们的形态差别很大，但主要部分均为变形虫状（amoeboid）并有丝状、网状或小管型支撑的假足。它们部分会制造可能有复杂结构的外壳或骨架，而这些外壳或骨架成为绝大部分的原生动物化石。它们差不多全部都拥有管状脊的线粒体。有孔虫界分为三类：

其他类别有可能被归入**虫类，但部分分支则较为接近有孔虫门。她们为Phytomyxea及Ascetosporea，分别为植物及动物的寄生生物，与及特别的阿米巴Gromia。有孔虫界的不同组别主要因为基因上的相似性而被认为是近亲。她们亦被认为是**虫类的伸延。有孔虫界的名称Rhizaria由Cavalier-Smith在2002年提出，他亦提出了Apusozoa及centrohelid的名称。

The Rhizaria are a species-rich supergroup of mostly unicellular eukaryotes. A multicellular form has also been described. This supergroup was proposed by Cavalier-Smith in 2002. Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all have mitochondria with tubular cristae.