''Symphysops'' is a genus of

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s of average size, belonging to the

Cyclopygidae Cyclopygidae is a family of asaphida, asaphid trilobites from the Ordovician. Cyclopygids had an extratropical Range (biology), distribution, and there is evidence that they lived in mesopelagic, darker parts of the water column (around 175m dee ...

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

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. It is twinned with Saint-Cirq-Lapopie in France. The village has a shop, a chip shop and a hairdress ...

). 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'' 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 An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

that merge at the front of the headshield (or

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 ...

) 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 ...

, 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 The fus ...

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

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

extant Extant or Least-concern species, least concern 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 * Exta ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

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 Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

)

synonym A synonym is a word, morpheme, or phrase that means precisely 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 a ...

''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 Nektonic trilobites