Zamani Island, Okinawa Prefecture, Japan
This is “star sand,” and the stars are forams of two species found widely in the Indo-Pacific, Baculogypsina sphaerulata (pointier) and Calcarina spengleri (blunter). Short for foraminifera, forams are single-celled organisms related to the amoeba, but with a hard shell called a test and one or more internal chambers. When they die, their tests accumulate as sand. Forams are abundant in the modern ocean’s waters as well as in the fossil record. Some float in the water column, others like star sand species live on the ocean bottom. There are also encrusting forams such as the red fragment in this sample, Homotrema rubrum.
In shape, forams vary from coiled (ammonite like) to round, elongated, leaf-like, flat, tubular, or conical. Forams eat decomposing plants and animals, bacteria and diatoms; they are food for worms, crustaceans, snails, fish, sea urchins and starfish.
“Star sand” is a popular souvenir from Japan.
Maximilian Dörrbecker (Chumwa) derivative work: Jon C CC BY-SA 3.0