''Symphysops'' is a genus of

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 ...

s of average size, belonging to the

Cyclopygidae Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had aextratropical distribution, and there is evidence that they lived in darker parts of the water column (around 175m deep). Cyclopygids are characterized by en ...

family. It had a cosmopolitan distribution and lived from the Middle to the Upper Ordovician (

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

Ashgill Ashgill is a village in South Lanarkshire, Scotland near Larkhall. It is part of the Dalserf parish. The village church dates back to 1889 The village has a shop The local school was first in Scotland to have an automated bell, installed in 1 ...

). It has been found in Canada (Quebec and Newfoundland), China, the Czech Republic (Bohemia), Iran, Ireland, Kazakhstan, Poland, Morocco, Spain, Scotland and Wales.Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997 The name ''Symphysops'' refers to the fused eyes, common to the species of this genus. Some (sub)species of the cyclopygid genera ''Cyclopyge'' and ''

Pricyclopyge ''Pricyclopyge'' is a genus of trilobites assigned to the family Cyclopygidae that occurs throughout the Ordovician. ''Pricyclopyge'' had aextratropical distribution, and there is evidence that it lived in darker parts of the water column (aroun ...

'' share this character, but ''Symphysops'' uniquely combines the merged eye with a frontal thorn on the head and the "lower eyelid".

Etymology

''Symphysops'' is the combination of the Ancient Greek σύν (syn) "together", φύσις (physis) "growth" and ὄψις (opsis) "sight", referring to the fused eyes.

Description

''Symphysops'' is characterized by large

eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conve ...

that merge at the front of the headshield (or cephalon) to form what looks like a

visor A visor (also spelled vizor) is a surface that protects the eyes, such as shading them from the sun or other bright light or protecting them from objects. Nowadays many visors are transparent, but before strong transparent substances such a ...

with at the back a wide free cheek. The remainder of the cephalon is filled by the

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

, which in most species extends into a forward pointing thorn at its frontal tip. The occipital ring cannot be distinguish from the rest of the glabella, which has two pair of transverse furrows, the rear pair distinct, and the frontal pair very shallow. The thorax consists of six segments, the frontal segment carrying backward directed pleural spines.

Ecology

''Symphysops'' has features typically associated with a pelagic lifestyle, among which very large eyes, compact thorax and indications of strong musculature. In some later cyclopygids, progressive enlargement resulted in the anterior fusion of their eyes. Given the weight of 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 c ...

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 ...

, it is likely cyclopygids swam upside down, not unlike some

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s with pelagic lifestyles. ''Symphysops'' is often found in the company of other pelagic trilobites such as ''Cyclopyge'', ''Degamella'', ''Opipeuterella'' and ''Carolinites''.

Species

* ''S. armatus'' ( Barrande, 1872) ( type)

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

''Aeglina armata'' * ''S. dejhaglensis'' Kolova, 1936 * ''S. mitrata'' (Novak, 1883) synonym ''Aeglina mitrata'' * ''S. sinensis'' Han, 1983 * ''S. spinifera'' Cooper & Kindle, 1936 * ''S. stevaninae'' López-Soriano & Corbacho, 2012 * ''S. subarmatus '' (Reed, 1914)'' ** ''S. subarmatus subarmatus'' ** ''S. subarmatus elongatus'' Kielan, 1959 * ''S. sulcatus'' (Barrande, 1872) synonym ''Aeglina sulcata''

References

{{Taxonbar, from=Q16992889 Cyclopygidae Asaphida genera Ordovician trilobites Fossils of Canada Fossils of China Fossils of the Czech Republic Fossils of Iran Fossils of Ireland Fossils of Kazakhstan Fossils of Poland Fossils of Morocco Fossils of Spain Fossils of Great Britain Prehistoric animals of China Middle Ordovician first appearances Late Ordovician extinctions Paleontology in Quebec Paleontology in Newfoundland and Labrador Paleozoic life of Quebec