#microfossil
- Acanthosphere — A rigid, spherical skeletal shell, either siliceous or calcareous, featuring prominent radiating, spine-like projections (acanthis), characteristic of certain microscopic marine protozoans such as radiolarians or acantharians. It serves a mechanical defense role and aids in buoyancy within the water column, while also being a crucial microfossil for dating geological strata.
- Alveolina — A genus of large fossil marine foraminifera, characteristic of the Late Cretaceous and Eocene periods, having a spherical, ellipsoidal, or fusiform calcareous shell structurally divided into numerous small chambers or alveoli; a microfossil belonging to this genus. These organisms represent essential index fossils for dating sedimentary geological layers and reconstructing ancient tropical marine environments.