Phylum Granuloreticulosa, class Foraminifera have a test1, which is often calcareous2 and resembles a microscopic shell. Through holes in the test, cytoplasm comes through to form a thin outer layer. From this layer arises an impressive network of reticulopodia3. In planktonic foraminifera, these reticulopodia are probably used for suspension and capturing/engulfing food particles. Foraminiferans are known for the accumulation of their calcareous tests in ocean sediments after they die. The fossil layers of foraminiferans have aided geological studies of ocean sediments.
1 A test is the outer hard shell of some spherical marine animals, another example of a test is in sea urchins.
2Containing or composting of calcium carbonate.
3 Fine threads that can form a large network which can be useful in entrapping prey.