Belongs within: Arachnida.
The Trigonotarbida are a group of fossil arachnids known from the late Silurian to early Permian (Dunlop & Selden 2004).
Characters (from Dunlop & Selden 2004): Opisthosoma with nine dorsal tergites divided into median and lateral plates; tergites 2 and 3 commonly fused into single macrotergite; two pairs of book-lungs present.
<==Trigonotarbida [Anthracomarti]
| i. s.: Palaeotarbus jerami (Dunlop 1996) H02
| Archaeomartus Størmer 1970 DS04
| Gilboarachne S07
|--Palaeocharinus Hirst 1923 [Palaeocharinidae] DS04
|--Lissomartus Petrunkevitch 1949 [Lissomartidae] RDS03
|--Kreischeria F04 [Kreischeriidae DS04]
| `--K. wiedei F04
|--Trigonotarbus [Trigonotarbidae] DR02
| `--T. arnoldi Petrunkevitch 1955 DR02
|--Anthracosironidae DS04
| |--Arianrhoda Dunlop & Selden 2004 DS04
| | `--*A. bennetti Dunlop & Selden 2004 DS04
| `--Anthracosiro Pocock 1903 DS04
| |--A. fritschi Pocock 1903 F04
| `--A. woodwardi Pocock 1903 F04
|--Aphantomartidae DS04
| |--Alkenia Størmer 1970 DS04
| | `--A. mirabilis Størmer 1970 DS04
| `--Aphantomartus Pocock 1911 RDS03
| |--*A. areolatus Pocock 1911 RDS03
| |--A. ilfeldicus (Scharf 1924) [=Eophrynus ilfeldicus] RDS03
| `--A. pustulatus (Scudder 1884) RDS03
|--Eophrynidae DS04
| |--Adelocaris peruvianus Packard 1889 F04
| |--Petrovicia Fritsch 1904 F04
| | `--*P. proditoria Fritsch 1904 F04
| |--Hemikreischeria Fritsch 1904 F04
| | `--*H. thevenini Fritsch 1904 [=Kreischeria geinitzii Brongniart 1901 (n. n.)] F04
| |--Stenotrogulus D07 [incl. Cyclotrogulus Fritsch 1904 RDS03]
| | |--S. salmii [=Eophrynus salmii] F04
| | `--‘Eophrynus’ sturii Hasse 1890 [=Cyclotrogulus sturii] F04
| `--Eophrynus Woodward 1871 RDS03
| |--E. prestwicii (Buckland 1837) F04, H02 [=Curculioides prestvicii H02]
| `--E. scharfi Scharf 1924 RDS03
`--Anthracomartidae [Anthracomatida] DR02
|--Maiocercus Pocock 1911 DR02
|--Coryphomartus Petrunkevitch 1913 DR02
|--Pleomartus Petrunkevitch 1945 DR02
|--Cleptomartus Petrunkevitch 1949 DR02
|--Cryptomartus Petrunkevitch 1949 DR02
|--Oomartus Petrunkevitch 1953 DR02
|--Brachylycosa Fritsch 1904 DR02
| `--*B. carcinoides [=Arthrolycosa carcinoides] F04
|--Vratislavia Fritsch 1904 F04
| `--*V. silesiaca (Röm. 1878) [=Architarbus silesiacus] F04
|--Brachypyge Woodward 1878 DR02
| |--B. carbonis Woodward 1878 [=Eophrynus carbonis] F04
| `--B. celtica Pocock 1902 F04
|--Promygale Fritsch 1901 [Promygalidae] DR02
| |--P. bohemica F04
| |--P. elegans F04
| `--P. rotundata F04
`--Anthracomartus Karsch 1882 DR02
|--*A. voelkelianus Karsch 1882 DR02
|--A. affinis Kušta 1885 F04
|--A. buchi (Goldenberg 1873) (n. d.) DR02
|--A. granulatus Fritsch 1904 DR02
|--A. hageni (Goldenberg 1873) (n. d.) DR02
|--A. krejcii Kušta 1883 F04
|--A. minor Kušta 1885 F04
|--A. palatinus Ammon 1900 F04
|--A. socialis Kušta 1888 F04
`--A. trilobitus Scudder 1885 F04
*Type species of generic name indicated
REFERENCES
[D07] Dunlop, J. A. 2007. Paleontology. In: Pinto-da-Rocha, R., G. Machado & G. Giribet (eds) Harvestmen: The Biology of Opiliones pp. 247–265. Harvard University Press: Cambridge (Massachusetts).
[DR02] Dunlop, J. A., & R. Rößler. 2002. The trigonotarbid arachnid Anthracomartus voelkelianus (Anthracomartidae). Journal of Arachnology 30 (2): 211–218.
[DS04] Dunlop, J. A., & P. A. Selden. 2004. A trigonotarbid arachnid from the Lower Devonian of Tredomen, Wales. Palaeontology 47 (6): 1469–1476.
[F04] Fritsch, A. 1904. Palaeozoische Arachniden. Selestverlag: Prague.
[H02] Harvey, M. S. 2002. The neglected cousins: what do we know about the smaller arachnid orders? Journal of Arachnology 30 (2): 357–372.
[RDS03] Rössler, R., J. A. Dunlop & J. W. Schneider. 2003. A redescription of some poorly known Rotliegend arachnids from the Lower Permian (Asselian) of the Ilfeld and Thuringian Forest Basins, Germany. Paläontologische Zeitschrift 77 (2): 417–427.
[S07] Shultz, J. W. 2007. A phylogenetic analysis of the arachnid orders based on morphological characters. Zoological Journal of the Linnean Society 150 (2): 221–265.