''Viaphacops'' 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 in the order

Phacopida Phacopida ("lens-face") is an order of trilobites that lived from the Late Cambrian to the Late Devonian. It is made up of a morphologically diverse assemblage of taxa in three related suborders. Characteristics Phacopida had 8 to 19 thorac ...

, family

Phacopidae Phacopidae is a family of phacopid trilobites that ranges from the Lower Ordovician to the Upper Devonian, with representatives in all paleocontinents. Description As in all Phacopina, the eyes (if present) consist of very large (0.5 mm in ' ...

, that lived during the Middle Devonian, and is known from North and South America (Bolivia,

Floresta Formation The Floresta Formation ( es, Formación Floresta, Df) is a geological formation of the Altiplano Cundiboyacense in the Eastern Ranges of the Colombian Andes. The sequence of siltstones, shales, coquinas and sandstone beds dates to the Devonia ...

Altiplano Cundiboyacense The Altiplano Cundiboyacense () is a high plateau located in the Eastern Cordillera of the Colombian Andes covering parts of the departments of Cundinamarca and Boyacá. The altiplano corresponds to the ancient territory of the Muisca. The Alti ...

, Colombia,Morzadec et al., 2015, p.342 and Venezuela), Asia (Central Kazakhstan and Far Eastern Russia).

Description

Like in all sighted Phacopina, the eyes of Viaphacops are compounded of very large, separately set lenses without a common cornea (so called schizochroal eyes), and like almost all other Phacopina, the articulate mid-length part of the body (or thorax) in Viaphacops has 11 segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct. The natural fracture lines (sutures) of the head run along the top edges of the compound eye. From the back of the eye these cut to the side of the head (

proparian 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 ...

) and not to the back. In front of the eye, the right and left facial sutures connect in front of the inflated glabella and consequently the free cheeks (or librigenae) are yoked as a single piece. The part of the skeleton that is "tucked under" (the doublure) has no sutures crossing it to form a rostral plate. The tailshield (or

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 ...

) is always smaller than the 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 ...

), a situation called micropygous. In the Phacopidae a merger of the anterior and the two pairs of neighbouring lobes of 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 ...

forms a frontal lobe that expands forward and can be inflated and overhanging the frontal border. To the back of the glabella two furrows (or sometimes one) cross the glabella forming two rings ("intercalating/pre-occipital ring" and "occipital ring"). The cephalon does not end in genal spines. The side lobes of the thorax (or pleurae, singular pleura) have rounded ends. The pygidium is well rounded, semicircular or shorter, with an entire margin, and without lateral and posterior projections. In many Phacopidae, where the facial sutures are apparently continuous and well developed, they were evidently nonfunctional in

ecdysis Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remna ...

, since no separate free cheeks can be found. ''Viaphacops'' is distinguished from related genera because the preoccipital furrow is merged with occipital furrow to form a deep broad furrow thus having obliterated the intercalating ring. The occipital ring itself is usually narrow. The vincular furrow, a trough in the cephalic doublure (ventral side of the border of the head) is deep, with a prominent inner border. The eyes are mostly moderate in size, but sometimes large. The tailshield is usually wide and weakly segmented. The surface of the glabella has fairly large tubercles.

References

Bibliography

* {{Taxonbar, from=Q22287038 Phacopidae Early Devonian first appearances Givetian extinctions Devonian trilobites of Asia Devonian trilobites of North America Devonian trilobites of South America Devonian Bolivia Fossils of Bolivia Devonian Colombia Fossils of Colombia Devonian Venezuela Fossil taxa described in 1972 Floresta Formation