Hyolitha

Hyoliths are an extinct group of invertebrates with small conical shells, known from fossils from the Palaeozoic era. They are at least considered lophotrochozoans, possibly being lophophorates, a group which includes the brachiopods (hyoliths may even be brachiopods themselves), while others consider them as being basal lophotrochozoans, or even molluscs.

==Morphology== The shell of a hyolith is typically one to four centimeters in length, triangular or elliptical in cross section. Some species have rings or stripes. It comprises two parts: the main conical shell (previously referred to as a 'conch') and a cap-like operculum. Some also had two curved supports known as helens They are calcareous – probably aragonitic All of these structures grew by marginal accretion.