Just like the shell of a clam, a pearl is composed of calcium carbonate (mainly aragonite or a mixture of aragonite and calcite). in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur.
Rimula is a genus of fungi in the Helotiales order. The relationship of this taxon to other taxa within the order is unknown (incertae sedis), and it has not yet been placed with certainty into any family. ^ Lumbsch TH, Huhndorf SM. (December 2007). Outline of Ascomycota â 2007.
Lingula is a genus of brachiopods in the class Lingulata. Lingula is known to have existed since the early Ordovician period. Lingula is a good example of a living fossil. Like all brachiopods, it is a filter feeder. Brachiopods are superficially similar to bivalves, both having two shells. Brachiopods are easily distinguished from molluscs because they have (different) dorsal and ventral shells.