''Soomaspis'' 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 ...

of small to average size (about 3 cm or 1.2-inch long) marine

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 ...

s in the Liwiidae Family, that lived during the late

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 ...

(early Hirnantian).

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains of ''Soomaspis'' were collected from the Soom Shale

Lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...

Western Cape The Western Cape is a province of South Africa, situated on the south-western coast of the country. It is the fourth largest of the nine provinces with an area of , and the third most populous, with an estimated 7 million inhabitants in 2020 ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

. ''Soomaspis'' looks like a large, soft

agnostid Agnostidae is a family of Agnostida trilobites. Like all Agnostina, they were eyeless and bore only two thoracic segments. They ranged in benthic waters across the globe from 508 to 461 million years ago, containing the following genera, among o ...

trilobite 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 ...

. 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

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). The genus is

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 ...

, its sole

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

being ''Soomaspis splendida''.

Etymology

The name of the genus is a compound word of the deposit where the species was collected (the Soom Shale), and the Greek word ''"

aspis An aspis ( grc, ἀσπίς, plural ''aspides'', ), or porpax shield, sometimes mistakenly referred to as a hoplon ( el, ὅπλον) (a term actually referring to the whole equipment of a hoplite), was the heavy wooden shield used by the infa ...

"'' (shield). The species epithet, ''splendida'' comes from the Latin word ''"splendere"'' (brightness).

Description

''Soomaspis splendida'' is estimated to be over 3 cm (1.2 inches) along the axis,L. Ramskold, J.-Y. Chen, G.D. Edgecombe, and G.-Q. Zhou (1996). "Preservational folds simulating tergite junctions in tegopeltid and naraoiid arthropods". ''

Lethaia ''Lethaia'' is a quarterly peer-reviewed scientific journal of Earth science, covering research on palaeontology and stratigraphy. Now published by Wiley-Blackwell, it was originally published by the International Commission on Stratigraphy. It is ...

'' 29: 15-20. , web
Preserv-folds
times longer than wide. 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

and two or three thoracic

s with articulating half-rings, all non-calcified, supposedly of medium convexity. The axis is poorly defined. The cephalon is transversely oval, widest at midlength. The cephalon is wider than the pygidium. Eyes are absent. Antennas are not known. The body is constricted at the three thoracic somites, so the animal gives the impression to have a waist. The pygidium is slightly wider than long, with the greatest width at midlength. The pygidium has a mid-ridge and five segments divided by clear furrows on the outer parts of the pleural field. The back edge of these furrows curve backwards, ending at a sharp angle to the pygidial margin.

Differences with other Liwiidae

*''Soomaspis splendida'' 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 thoracic somites instead of 4. ''S. splendida'' has a mid-length ridge on the pygidium and furrows on the outer parts of the pleural field, which are unknown from ''Liwia''. ''Soomaspis'' also has a pygidium with an entire margin, while ''Liwia'' has five pairs of modest marginal spines, and a concave posterior border. *''S. splendida'' 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 ''Soomaspis'' have an entire margin and a mid-ridge on the pygidium in common. *''S. splendida'' differs from ''

Tariccoia arrusensis ''Tariccoia'' is a genus of nektaspid arthropods belonging to the family Liwiidae, known from fossils found in Ordovician strata in Sardinia and Morocco. It is between and long. It has a headshield (or cephalon) wider than the tailshield (pygi ...

'', that lacks visible segmentation of the pygidium. The surface of the exoskeleton of ''S. splendida'', particularly the pygidium, shows dense pitting, while it is smooth in ''T. arrusensis''. ''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

''Soomaspis splendida'' has been collected from the Soom Shale (early

Hirnantian The Hirnantian is the final internationally recognized stage of the Ordovician Period of the Paleozoic Era. It was of short duration, lasting about 1.4 million years, from to Ma (million years ago). The early part of the Hirnantian was charact ...

), Keurbos Farm, near Clanwilliam, Cape Province, South Africa.

Habitat

''Soomaspis splendida'' was probably a marine bottom dweller. The Soom Shale is sometimes interfingered with the glacial

tillite image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

of the Pakhuis Formation, indicating that ''Soomaspis'' lived in the open sea, near the edge of an ice sheet.

References

{{Taxonbar, from=Q6459255 Nektaspida Ordovician arthropods Ordovician animals of Africa Hirnantian Soom Shale fossils