''Tariccoia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

nektaspid Nektaspida (also called Naraoiida, Nektaspia and Nectaspida) is an extinct order (biology), order of non-Mineralized tissues, mineralised artiopodan arthropods. They are known from the mid-Cambrian to the upper Silurian. Originally classified as t ...

arthropods belonging to the family

Liwiidae Liwiidae is a family of arthropods in the order Nektaspida. Members are known from the Cambrian and Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 mill ...

, known from fossils found in

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

strata in

Sardinia Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label=Algherese and Catalan) is the second-largest island in the Mediterranean Sea, after ...

and Morocco. It is between and long. It has a headshield (or

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

) wider than the tailshield (

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

), and in between them three (or four?)

thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...

body segments (

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide in ...

s).

Etymology

The name of the genus references the Sardinian paleontologist M. Taricco. The species was named after the Riu is Arrus Member, the deposit in which it was found.

Description

''Tariccoia arrusensis'' is between 2.5 and 6 cm along the axis, almost half a wide as long. The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...

consists of a cephalon, a pygidium and two or three thoracic somites with articulating half-rings, all non-calcified. The cephalon is sub-semicircular, widest near the rounded genal angles. The cephalon is wider than the pygidium. Eyes are absent. Antennas are not known. The body is constricted at the two or three thoracic somites, so the animal gives the impression to have a waist. The pygidium is widest before midlength. The pygidium has a mid-ridge.

Differences with other Liwiidae

*''Tariccoia arrusensis'' differs from ''

Liwia ''Liwia'' is a genus of nektaspid, a soft-bodied stem-group chelicerate. It includes the following species, both are known from borehole samples several kilometers in depth from the Zawiszyn Formation in Poland, which has also yielded ''Peytoia ...

'' by having 3 clearly visible thoracic somites (perhaps a 4th is obscured by the cephalon) instead of 4. ''T. arrusensis '' has a mid-length ridge on the pygidium, which is not known from ''Liwia''. ''Tariccoia'' also has an oval pygidium with an entire margin, while ''Liwia'' has five pairs of modest marginal spines, a straight anterior border and a concave posterior border. *''T. arrusensis'' differs from '' Buenaspis forteyi'', that has a cephalon and pygidium that are not wider than its 6 thoracic somites. The pygidium of ''B. forteyi'' is wider than long, with a straight anterior border. ''Buenaspis'' and ''Tariccoia'' have an entire margin and a mid-ridge on the pygidium in common. *''T. arrusensis'' differs from '' Soomaspis splendida'', that has an oval cephalon, and lacks visible segmentation of the pygidium. ''Tariccoia'' and ''Soomaspis'' both have a broad doublure and lack a lengthwise mid-ridge on the cephalon. In both species the pygidium is about as long as wide, but in ''Soomaspis'' the widest point is around midlength, while ''Tariccoia'' is widest in the frontal half. The species share 3 thoracic somites, an entire margin and a mid-ridge on the pygidium.

Distribution

''T. arrusensis'' has been collected from the Upper Ordovician (

Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million yea ...

Katian The Katian is the second stage of the Upper Ordovician. It is preceded by the Sandbian and succeeded by the Hirnantian Stage. The Katian began million years ago and lasted for about 7.8 million years until the beginning of the Hirnantian million ...

) Riu is Arrus Member, Monte Argentu Formation, Sardinia, Italy. ''T.'' ''tazagurtensis'' has been collected from the

Fezouata Formation The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Early Ordovician.

of Morocco dating to the Early Ordovician (

Tremadocian The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from to million years ago. The base of the Tremadocian is defined as the first appearance of the ...

Habitat

''Tariccoia arrusensis'' is thought to have lived in a restricted reduced oxygen marine environment close to shore such as a lagoon or a bay in what was then the cold high-latitude margin of southern Gondwana, where it was locally abundant alongside macroscopic algae. ''Tariccoia tazagurtensis'' also lived in cold waters in high-latitude southern Gondwana, but it was an extremely rare member of the fauna and lived in open shallow-marine conditions.

References

{{Taxonbar, from=Q7686010 Nektaspida Ordovician arthropods Fossils of Italy Animals described in 1990 Katian