''Cheloniellon'' is a

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 "unisp ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

cheloniellid Cheloniellida is a taxon (usually referred to as an order) of extinct Paleozoic arthropods. As of 2018,Wendruff, Andrew James, et al. "New cheloniellid arthropod with large raptorial appendages from the Silurian of Wisconsin, USA." BioRxiv (2018) ...

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

, known only by one species, ''Cheloniellon calmani'', discovered from the Lower Devonian Hunsrück Slate of

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

Morphology

''Cheloniellon'' range about 20 centimeters in body length (excluding appendages). The flattened, ovoid body compose of 11 tergites (dorsal exoskeleton), all but the posteriormost are laterally expanded and covered the appendages underneath each of them. The boundaries between tergites have a radiated appearance. Dorsal surface of the first tergite have a pair of kidney-shaped eyes. Based on the differentiation of corresponding appendages, the first 2 tergites and the remaining 9 tergites were interpreted as those of

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino Jr., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont ...

(head) and trunk, respectively. Contray to the widely-referred reconstruction by Stürmer & Bergström (1978), but as most of the Cheloniellids, There is no evidence of

telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...

(a medial tail-like terminal structure) in any described fossil materials.Wendruff, Andrew James, et al. "New cheloniellid arthropod with large raptorial appendages from the Silurian of Wisconsin, USA." BioRxiv (2018): 407379

/ref> Underneath the tergites were numerous pairs of appendages. The anteriormost appendage pair were Antenna (biology), antennae, followed by a pair of specialized second appendages that bore spines and esthetasc-like brushes, and 4 pairs of leg-like appendages that have overlapped gnathobases (jaw-like structure on leg base). The mouth was covered by a labrum with spiny surface, situated between the second appendages and the first gnathobasic appendages. The last gnathobasic appendage pair and the remaining 5 appendage pairs anterior to it were interpreted as corresponding to the second tergite and first tergite, respectively. Appendages posterior to the cephalon were 8 pairs of biramous appendages (each compose of a leg-like endopod and a lobe-like exopod) and a pair of furcae, corresponding to the remaining 9 trunk tergites.

Paleoecology

''Cheloniellon'' may have been a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

, using its gnathobases to crush prey while the spiny labrum may have helped lead food items toward the mouth opening. The specialized second appendages are too fragile to be

raptorial In biology (specifically the anatomy of arthropods), the term ''raptorial'' implies much the same as ''predatory'' but most often refers to modifications of an arthropod leg, arthropod's foreleg that make it function for the grasping of prey whi ...

, instead they may have played a tactile role, sensing the property and position of food items. The endopod and exopod of the trunk appendages may have had a locomotory and respiratory function, respectively.

Classification

''Cheloniellon'' is a genus of Cheloniellida, an extinct

taxon that have a controversial phylogenetic position. It was previously thought to be

chelicerate The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks ...

-related, but later studies repeatedly suggests it as a member of

Artiopoda Artiopoda is a clade 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 Trilobitomor ...

, forming the clade

Vicissicaudata Vicissicaudata is an unranked group of artiopodan arthropods, containing Cheloniellida, Aglaspidida and several other genera outside these groups like ''Sidneyia'' and ''Emeraldella.'' Description Vicissicaudatans are similar to most other ...

with

Aglaspidida Aglaspidida is an extinct order of marine arthropods known from fossils spanning the Middle Cambrian to the Upper Ordovician. Initially considered chelicerates, modern anatomical comparisons demonstrate that the aglaspidids cannot be accommodated ...

and related genera. Within Cheloniellida, ''Cheloniellon'' branched next to '' Neostrabops'' but basal to '' Triopus'' and '' Duslia''.

References

{{Taxonbar, from=Q96386650 Devonian animals of Europe Fossils of Germany Hunsrück Slate fossils Fossil taxa described in 1932 Artiopoda