Nonionidae

Nonionidae is a family of foraminifera belonging to the order Rotaliida. These marine protists are characterized by their planispiral or slightly trochospiral tests (shells) that are composed of radially arranged, granular calcite. The chambers are typically inflated and the sutures are generally distinct and depressed. The aperture is interiomarginal and may be a simple slit or a series of pores.

Nonionids are found in a variety of marine environments, ranging from shallow coastal waters to deep-sea settings. They are often abundant in brackish water and estuarine environments. The family has a long geological history, with fossils dating back to the Paleocene epoch.

Systematic classification within the Nonionidae can be complex and based on subtle morphological features of the test. Important genera within the family include Nonion, Nonionella, and Astrononion. Identification to species level often requires detailed microscopic examination of the test structure.

Nonionids play a role in marine ecosystems as grazers on bacteria and algae, and they also serve as a food source for larger organisms. Their fossilized tests are also used in biostratigraphy and paleoenvironmental reconstructions, providing information about past ocean conditions. The distribution and abundance of different Nonionid species can be sensitive indicators of environmental changes, such as salinity, temperature, and nutrient levels.