Tentaculitidae

Tentaculitidae is an extinct family of fossil organisms belonging to the class Tentaculoida, which are often considered early mollusks. These organisms are characterized by their slender, conical, and often curved shells, which are typically straight or slightly curved and ornamented with fine transverse rings. The shells, or "tests," are generally small, ranging from a few millimeters to a few centimeters in length. They are commonly found in Paleozoic marine sedimentary rocks, particularly from the Silurian and Devonian periods.

The exact taxonomic placement of Tentaculitidae has been a subject of debate among paleontologists. Historically, they have been assigned to various phyla, including Annelida and Mollusca. More recently, they have been grouped within their own class, Tentaculoida, often placed within or near Mollusca due to certain shell microstructural similarities. Their lifestyle is thought to have been benthic, meaning they lived on the seafloor, and their mode of life, whether sessile or mobile, remains uncertain. Fossil evidence suggests they inhabited a variety of marine environments. The distribution of Tentaculitidae fossils is widespread, indicating a global presence during their time. Their distinctive shell morphology makes them useful index fossils for correlating rock strata from the Paleozoic era.