Asterocéphalans

Asterocéphalans are a proposed taxonomic group within the phylum Echinodermata. This classification is not universally accepted within the scientific community and is often considered an informal or provisional grouping rather than a formal taxonomic rank. The term "asterocéphalans" is generally used to encompass a broad collection of echinoderms that exhibit a star-like or radial symmetry, a characteristic feature of the phylum. This broad definition would typically include organisms like starfish (Asteroidea), brittle stars (Ophiuroidea), and possibly some extinct forms.

The concept of asterocéphalans arises from early attempts to categorize the diversity of echinoderms based on observable morphological traits. While radial symmetry is a defining feature of echinoderms, the specific arrangements of their body parts, such as the number of arms or the presence of specific skeletal elements, led to the development of distinct classes like Asteroidea and Ophiuroidea. The idea of a single "asterocéphalans" group tends to overlook the significant evolutionary divergences and specialized adaptations that distinguish these various classes.

Modern echinoderm classification relies heavily on molecular data and detailed comparative anatomy, which reveal more complex evolutionary relationships than those suggested by simple radial symmetry. Consequently, while the term "asterocéphalans" might occasionally appear in older literature or informal discussions, it is largely superseded by the established classes and their phylogenetic relationships within the phylum Echinodermata. Scientists currently focus on the recognized classes, each with its own unique evolutionary history and characteristics.