Gromia is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. Gromia are ameboid, producing filose pseudopodia that extend out from the cell's proteinaceous test through a gap enclosed by the cell's oral capsule. The test, a shell made up of protein that encloses the cytoplasm, is made up of several layers of membrane, which resemble honeycombs in shape – a defining character of this genus.

Gromia were first discovered in shallow waters, with members of the best-characterized species Gromia oviformus often found inhabiting rock surfaces, sediments, or seaweed holdfasts. However, research from the 1990s and early 2000s identified gromiids inhabiting depths up to 4,392 m, leading to several new deep-sea Gromia species being described and recognized.

A recent study of the deep-sea species Gromia sphaerica revealed that it produces traces on the seafloor which resemble fossil traces formerly attributed to early Bilateria (animals with bilateral symmetry); this now calls into question whether such fossil traces are reliable as documentation of early multicellular animal diversification in the Precambrian era.

Deep-sea gromiids have also been shown to be important for carbon cycling and denitrification.

Gromia were first described in the 1835, with G. oviformis gaining prominence because it was often found in the intertidal zones on the British coast. Initially, Gromia were regarded as members of Foraminifera or Filosea, as noted in a review by Cifelli (1990).

Gromia became better characterized throughout the 1960s, when electron microscopy revealed more details on their morphology, including their honeycomb membranes.

The first molecular studies involving Gromia, which sampled G. oviformis, used small subunit (SSU) ribosomal RNA genes and concluded that Gromia were members of Cercozoa, a large group of amoebae with tests and filose pseudopodia. Follow-up studies on this group placed Gromia within the Gromiidea class, again based on SSU rRNA genes Eventually, when molecular studies combined data from several genes – actin, polyubiquitin, RNA polymerase II and small subunit rRNA genes – Gromia was shown to be a sister group to Foraminifera. Moreover, within the genus Gromia, studies of the small subunit ribosomal RNA genes of various deep-sea gromiids has revealed species diversity within Gromia, with molecular data tending to correlate with distinct morphologies of the various species’ tests.

Gromia were long thought to only inhabit shallow waters, until samples from the Arabian Sea from depths below 1,000 m revealed the first deep-sea gromiid – Gromia sphaerica. Additional species of deep-sea Gromia protists were later described in waters from the Arabian sea, the European Arctic sea, and off the coast of Antarctica, among other locations, and characterized both morphologically and through molecular studies of their small subunit rRNA genes.