''Acanthomeridion'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

found in the

Chengjiang fauna The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales ...

deposits of

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. In 1997, it was placed in its own,

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

, Acanthomeridiidae. It is known from eight specimens, all found in China.

Morphology

''Acanthomeridion'' was a 35 mm-long animal, with 11 segments ending in rear-facing spines. The head features free cheeks separated from the rest of the head by sutures. This is analogous with

trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

. Otherwise, affinities are mainly unclear. More recently discovered specimens of the species ''Acanthomeridion anacanthus'' have paired gut diverticula as have been seen in

artiopods The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilo ...

. No fossils exposing the limbs have yet been found, but they are thought to be

biramous The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plur ...

with the upper section of the limb holding the gills. As limbs have not been found, it is uncertain whether ''Acanthomeridion'' was a seafloor-dweller or a swimmer. The streamlining suggests that it swam, but is inconclusive.

Taxonomy

''Acanthomeridion'' is considered a primitive member of

Artiopoda The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilo ...

. Some studies have put it as having affinities with petalopleurans or xandarellids, but a more recent study by Hou, Williams ''et al.'' including the more recently discovered specimens suggest that it is the most basal member of the clade.

References

Maotianshan shales fossils Prehistoric arthropod genera Monotypic arthropod genera Arthropod enigmatic taxa {{paleo-arthropod-stub