Tentaculites is an extinct genus of molluscs known from Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 age fossils, ranging from 360-410 million years ago. The taxonomic classification of tentaculitids is uncertain, but some group them with pteropods. They may also be related to other conical shells of uncertain affinity including cornulitids, microconchids

Microconchida

The Order Microconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes found from the Upper Ordovician to the Middle Jurassic around the world . They have lamellar calcitic shells, usually with pseudopunctae or punctae and a bulb-like origin...

 and trypanoporids

Trypanoporida

Trypanoporida is an extinct order of encrusting animals from the Tentaculita class, which were common in the Devonian oceans . Their affinity is unknown; they have been placed among worms and corals. They appear to be closely related to other taxa of uncertain affinity, including the...

. Tentaculitids have ribbed, cone-shaped shells which range in length from 5 to 20 mm.

Further reading

• Treatise on Invertebrate Paleontology, Part W - Miscellanea. Geological Society of America and University of Kansas Press, 1962. LCCN
  Library of Congress Control Number
  The Library of Congress Control Number or LCCN is a serially based system of numbering cataloging records in the Library of Congress in the United States...
  
  53012913