''Villebrunaster'' is an extinct genus of starfish-like animal belonging to

Asterozoa The Asterozoa are a subphylum in the phylum Echinodermata. Characteristics include a star-shaped body and radially divergent axes of symmetry. The subphylum includes the class Asteroidea (the starfish), the class Ophiuroidea (the brittle stars ...

that lived around 480 million years ago during Early Ordovician Period in modern-day southern

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

and

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to ...

. As of 2022, it contains two species, namely ''V. thorali'' and ''V. fezouataensis''. ''V. thorali'' was described in 1951 and ''V. fezouataensis'' was described in 2021. ''Villebrunaster'' represents one of the oldest members of asterozoans, and perhaps, according to a description in 2021, the earliest divergent stem-group (ancestral members) of Asterozoa.

Discovery and species

The first species was discovered and described by British palaeontologist William Kingdon Spencer in 1951. The fragmentary specimens were collected from

Saint-Chinian Formation The Saint-Chinian Formation is a geological formation composed of shales with limestone inclusions, dating from the Lower Ordovician (Tremadocian). It is one of the six geological formations from the Saint-Chinian Cambro-Ordovician basin, compri ...

in southern France. Spencer recognised it as among "the earliest starfish known." Another British palaeontologist Juliette Dean Shackleton identified new specimens as ''Ampullaster ubaghsi'' in 2005, which were later reclassified as ''V. thorali.'' The second species, ''V.'' ''fezouataensis,'' was described by Aaron W. Hunter and Javier Ortega-Hernándezas at the University of Cambridge as ''Cantabrigiaster fezouataensis'' in 2021. The specimens, originally collected from Fezouata Shale Formation in Morocco, were reanalysed by American palaeontologist Daniel B. Blake and Frederick H.C.Hotchkiss who moved to taxonomic position the genus ''Villebrunaster'' in 2022.

Description

The body of ''Villebrunaster'' is that of a typical starfish having five radiating arms. Mouth is at the centre of the body. The mouth region is composed of three types of endoskeletons called

ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...

, such as half-cylinders or the ambulacral, virgal that form skeleton between the ambulacral, and a pair of mouth plates that radiate into the mouth opening. The arms are broad and evenly arranged to form pentagonal structure. The presence of virgal ossicles is a feature of Somasteodea. However, ''Villebrunaster'' lacks axially oriented ossicles along the lateral margins of the arms, which are found in somasteroids. This suggests that it is a primitive member of the group. The radial water channel are large and run close to the ventral side of the body, while the transverse water channels small and difficult to recognise. The ossicle series are larger in ''V.'' ''fezouataensis'' than in ''V. thorali.''

Evolutionary importance

Phylogenetic analysis indicate that ''Villebrunaster'' is oldest known and the earliest diverging group among Asterozoa, a group that includes

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

brittle stars Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

and basket stars. The absence of some ambulacral ossicles but presence of virgal ossicles show that the development and variation of ossicles are the important features in the evolution of later asterozoans. However, the genus does not necessarily represent the common ancestor of Asterozoa.

References

{{Taxonbar, from=Q21229665 Fossil taxa described in 1951 Prehistoric Asterozoa genera Prehistoric life of Europe Prehistoric life of Africa