[4] Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera and Radiolaria have a symbiotic relationship with unicellular algae.

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.

They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.

This includes the causative agent of Denman Island Disease, Mikrocytos mackini a small (2−3 μm diameter) amitochondriate protistan.

In his 1861 classification of the Rhizopoda (amoebae), the zoologist William B. Carpenter proposed the order Reticularia, which consisted of Foraminifera and Gromiida on the basis of their very similar thin, reticulose pseudopodia with granules circulating inside.

[12] However, the idea that these organisms and others such as Radiolaria were all related to one another emerged rather recently, with the help of molecular phylogenetics and advanced microscopy techniques in the late 20th century.

[20] Imbricatea Thecofilosea Sarcomonadea (paraphyletic) Helkesea Metromonadea Granofilosea Chlorarachnea Phytomyxea Gromiidea Lapot gusevi Foraminifera Polycystinea Acantharea Sticholonchea Stramenopiles Alveolata Complete sexual life cycles have been demonstrated for two lineages (Foraminifera and Gromia) and direct evidence for karyogamy or meiosis has been observed in five lineages (Euglyphida, Thecofilosea, Chlorarachniophyta, Plasmodiophorida and Phaeodarea).