Tentaculites is an extinct genus of conical fossils of uncertain affinity, class Tentaculita, although it is not the only member of the class. It is known from Lower Ordovician to Upper Devonian deposits both as calcitic shells with a brachiopod-like microstructure and carbonaceous 'linings'. The "tentaculites" (i.e. tentaculita) are also referred to as the styliolinids. Affinity The taxonomic classification of tentaculitids is uncertain. Some grouped them with pteropods, but there is no modern support and only superficial similarity. They may also be related to other conical shells of uncertain affinity including cornulitids, Anticalyptraea, microconchids and trypanoporids. Their shell microstructure has warranted their comparison with the brachiopods and phoronids, and the possible Ediacaran lophophorate Namacalathus. Morphology Tentaculitids have ribbed, cone-shaped shells which range in length from 5 to 20 mm. Some species septate; their embryonic shell, which is retained, forms a small, sometimes spherical, chamber. Ecology Some species are inferred to have been planktonic. See also Mari Mari Group, fossil formation in the state of Amazonas of northwestern Brazil References Further reading Treatise on Invertebrate Paleontology, Part W - Miscellanea. Geological Society of America and University of Kansas Press, 1962. LCCN 53012913 Devonian animals Late Devonian animals Tentaculita Early Ordovician first appearances Late Devonian genus extinctions Silurian animals of North America Paleozoic life of Ontario Paleozoic life of Alberta Paleozoic life of the Northwest Territories Paleozoic life of Nova Scotia Paleozoic life of Quebec Paleozoic life of Yukon