Homotrema

Homotrema is a genus of small, reddish-pink foraminifera, which are single-celled organisms belonging to the phylum Rhizaria. These marine protists are sessile and encrusting, meaning they attach themselves to hard substrates such as shells, rocks, and other organisms. They are particularly common in tropical and subtropical waters, often found on the undersides of corals and other reef-associated structures.

The tests, or shells, of Homotrema are typically irregular in shape, though they can form a lobed or branching structure. They are calcareous, composed of calcium carbonate, and their distinctive color comes from symbiotic algae, called zooxanthellae, that live within their tissues. These algae provide the foraminifera with nutrients through photosynthesis, while the foraminifera offer the algae a protected environment.

Homotrema are important contributors to reef ecosystems. Their tests, upon the death of the organism, become part of the carbonate sediment that forms beaches and other reef structures. They are also a food source for some small invertebrates. While they are widespread, their presence can sometimes indicate specific environmental conditions. Identification of species within the genus Homotrema relies on detailed examination of their test morphology and internal structures.