Ductina

{{Short description|Genus of extinct trilobites}} {{Automatic Taxobox | fossil_range = {{Geological range|411|359|Pragian to Famennian}} | image = Trilobite Ductina.jpg | image_caption = ''Ductina vietnamica'' | taxon = Ductina | authority = Richter and Richter, 1931 | subdivision_ranks = Species | subdivision = * ''D. ductifrons'' (R. & E. Richter, 1926) (Type) synonym ''Phacopidella ductifrons'' * ''D. vietnamica'' (Maximova, 1965) }}

'''''Ductina''''' is a genus of extinct, small to average sized, eyeless phacopid trilobite, that lived during the Devonian.

== Description ==

The body of ''Ductina'' is small to average (up to {{convert|5|cm|in}}), {{frac|1|1|4}} to 2 times as long as wide, blunted oval. Body without any adornment. The headshield (or cephalon) is 2 to 3 times as wide as it is long in the direction of the axis (or sagittally). The cephalic axis (or glabella) is strongly widening forward with shallow furrows, the front curving downward to end at an approximate straight angle to the plain of the axis. Another shallow furrow (the occipital furrow), with left and right a deep pit (apodemal pit), crosses to the back of the glabella to define a narrow band (or occipital ring), and just in front left and right a small lobe is defined by shallow furrows and a deep pits. The back of the cephalon is often broken, obscuring the features of the occipital ring. Eyes and eye ridges (palpebral lobes) are absent.<ref>Dele, D.M. Secondary Blinding among the Phacopid Trilobites and its Significans. American Midland Naturalist, 18/6. 1937</ref> The natural fracture lines (sutures) of the cephalon coincide with its margin (unique with the Phacopidae), so there are no free cheeks (or librigenae). The genal angles are rounded, not truncated, no genal spine. The thorax has 10 segments, and the width of the axis is about {{frac|1|3}} of the thorax. Tailpiece (or pygidium) is 20 to 35% of the length of the body. The pygidial axis (or rachis) is pointed (or acute), ending at the border.<ref>Struve, W. Suborder Phacopina, p. O467. ''in'' Moore, R.C. (ed.). Treatise on Invertebrate Paleontology. Part O – Arthropoda (Trilobitomorpha). 1959</ref>

== Distribution ==

The species of the genus ''Ductina'' lived during the Devonian in Europe and South-East Asia.

Fossils of ''D. vietnamica'' have been found in the Eifelian of China (Nandan Formation, Luofu, Nandan County, Guangxi Province {{Coord|24|30|N|115|36|E}},<ref name="Wang">Wang, Y., A. J. Boucot, J.Y. Rong and X.C. Yang. Community paleoecology as a geologic tool: the Chinese Ashgillian-Eifelian (latest Ordovician through early Middle Devonian) as an example. Geological Society of America Special Paper 211:1-100. 1987</ref> and Hunan Province); and in the Pragian of Vietnam (Song Hiem, Mia Le Beds {{Coord|22|12|N|106|12|E}}).<ref name="Tong-Dzuy">Tong-Dzuy, E. T., T. H. Dang, D. H. Nguyen, D. K. Nguyen, H. H. Nguyen, T. D. Nguyen, H. P. Ta, K. N. Pham, and N. T. Doan. 1988. Stratigrafiya i tselenteraty Dewona W'etnama, 1: Stratigrafiya [Devonian stratigraphy and coelenterata of Vietnam, 1: Stratigraphy] 5-184</ref>

Fossils of ''D. ductifrons'' have been found in the Famennian<ref>Brauckman, C. and B. Famennian Trilobites: An Outline of their Stratigraphical Importance. Belgian Ministry of Economic Affairs, Administration of Mines, Belgian Geological Survey, T109, pp. 9-17. 1986 [http://popups.ulg.ac.be/ASGB/docannexe.php?id=2365] {{Webarchive|url=https://web.archive.org/web/20120508081512/http://popups.ulg.ac.be/ASGB/docannexe.php?id=2365 |date=2012-05-08 }}</ref> of the United Kingdom, Germany (Eskesberg, Nehden,[http://www.trilobita.de/phacopida4.htm] Varresbeck,[http://www.philfossil.de/Palaeozikum/Devon/Devon.htm] {{Webarchive|url=https://web.archive.org/web/20120426091547/http://www.philfossil.de/Palaeozikum/Devon/Devon.htm |date=2012-04-26 }} all near Wupperthal), Poland (near Psiarnia, in the Southern part of the Holy Cross Mountains {{Coord|50|53|N|20|55|E}}),<ref name ="Osmolska">Osmolska, H. Famennian Phacopidae from the Holy Cross Mountains (Poland). Acta Palaeontologica Polonica, Volume 3, nr. 2, 1953 [http://www.app.pan.pl/archive/published/app03/app03-119.pdf]</ref> and the Western Urals in Russia.<ref name ="Osmolska"/>

== Habitat == All phacopids were probably marine bottom-dwellers. ''D. vietnamica'' has been found with several open water species (Nandan Formation in Guanxi, China), indicating deep and dark waters, probably poor in oxygen near the bottom where ''Ductina'' lived.<ref name="Wang"/> It has also been found as part of a species rich community characteristic of a shallow coral sea.<ref name="Tong-Dzuy"/>

== Key to the species == {| |- valign="top" align="left" ! scope="row" width="3%" | '''1''' | Body symmetrically elliptic, {{frac|1|1|4}} to {{frac|1|1|2}} times as long as wide, retaining the same width over the frontal half of the thorax. Glabellar furrow evenly shallow and discernible to the cephalic margin. Pygidium 2 times or more wider than long. Rachis has shallow but clear furrows, is narrowly triangular, with sides bending inward towards the back, to end at an angle of about 45° with the axis. Famennian. United Kingdom; Eifel and Thüringen, Germany; Holy Cross Mountains, Poland; West side of the Urals, Russia. → '''''D. ductifrons''''' |- valign="top" align="left" ! scope="row" width="3%" | '''-''' | Body slightly reverse egg shaped, {{frac|1|2|3}} to 2 times as long as wide, widest at the back of the cephalon, the thorax slightly tapering backwards. Glabellar furrow quickly shallower and indiscernible near the cephalic margin. Pygidium {{frac|1|1|4}} to {{frac|1|1|2}} times wider than long. Rachis has faint, hardly discernible furrows, is narrowly triangular with approximate straight sides along the length. Pragian to Eifelian. Guangxi and Hunan, Southern China; Vietnam. → '''''D. vietnamica''''' |}

<gallery mode=packed> File:Ductina ductifrons.jpg|''Ductina ductifrons'', from Wupperthal, Germany File:Ductina vietnamica 2 lateral.jpg|''Ductina vietnamica'', lateral view File:Ductina vietnamica 2 frontal.jpg|''Ductina vietnamica'', frontal view File:Ductina vietnamica dorsal.jpg|''Ductina vietnamica'', dorsal view </Gallery>

== References == {{Reflist}}

Category:Phacopidae Category:Devonian trilobites of Europe Category:Fossils of China Category:Fossils of Germany Category:Fossils of Poland Category:Fossils of Russia Category:Fossils of Sweden Category:Fossils of Great Britain Category:Fossils of Vietnam Category:Early Devonian first appearances Category:Famennian extinctions Category:Devonian trilobites of Asia Category:Phacopida genera