Asterocéphalan

Asterocéphalan is a term used in the field of paleontology to describe a group of extinct marine animals that lived during the Ordovician and Silurian periods, approximately 485 to 419 million years ago. These animals are characterized by their unique body structure, which consists of a central, star-shaped body (hence the name "asterocéphalan," derived from the Greek words "aster" meaning star and "kephalé" meaning head) surrounded by a ring of tentacles. The central body is believed to have housed the animal's digestive system and reproductive organs, while the tentacles were used for feeding and possibly for locomotion.

Asterocéphalans are considered to be the earliest known members of the phylum Echinodermata, which includes modern-day animals such as starfish, sea urchins, and sea cucumbers. They are thought to have evolved from a group of animals known as blastozoans, which were also characterized by a central body surrounded by tentacles. The transition from blastozoans to asterocéphalans marked an important step in the evolution of echinoderms, as it laid the groundwork for the development of the unique body plans seen in modern echinoderms.

Fossils of asterocéphalans have been found in a variety of marine environments, including shallow seas and deep-sea trenches. They are typically preserved as internal molds or casts, which reveal the intricate details of their body structure. Despite their importance in the evolutionary history of echinoderms, asterocéphalans are relatively rare in the fossil record, and much about their biology and ecology remains unknown. Ongoing research continues to shed light on the fascinating world of these ancient marine animals.