Tentaculites

Tentaculites are an extinct group of marine invertebrates that lived during the Paleozoic Era, from the Cambrian to the Devonian periods. They are characterized by their long, slender, conical shells, which are typically straight or slightly curved. These shells, known as tests, were composed of calcium carbonate and were often ornamented with fine growth rings. The shell opening was usually simple, though some species had a slightly constricted aperture.

The exact classification of tentaculites has been a subject of debate among paleontologists. For a long time, they were considered mollusks, but their unique shell structure and internal anatomy led to comparisons with other phyla. More recently, they have been placed in their own phylum, Tentaculita, reflecting their distinct evolutionary lineage. Some researchers have also suggested possible affinities with annelid worms or other lophophorate groups.

Tentaculites are found as fossils in marine sedimentary rocks worldwide. Their abundance in certain formations suggests they lived in large numbers, likely as planktonic or nektonic organisms, drifting or swimming in ancient seas. Their feeding habits are not well understood, but the shell morphology suggests they may have been filter feeders, straining small particles from the water. The demise of tentaculites at the end of the Devonian period may be linked to broader extinction events that reshaped marine ecosystems. Their fossils are valuable for biostratigraphy, helping to date rock layers from the Paleozoic.