Belongs within: Sclerosomatidae.
Prionostemma is a genus of sclerosomatid harvestmen recognised from Central and South America, the defining characters of which remain poorly defined.
Characters (from Roewer 1923): Eyemound as long as high and wide or wider, dorsally smooth or granular. Scutum unarmed. Lateral margins of coxae with sharp, three-pointed denticulations. Legs very long and thin; femur II 2–3 (or more) times and femora I and III 1.5–2 times as long as body; femora I–IV with nodular formula 0.3.0.1.
<==Prionostemma Pocock 1903T-D04 [=Prionomma Loman 1902 non White 1853C92] |--P. retusumHT12 `--+--P. ingleiHT12 `--P. intermedium (Banks 1909)HT12, R23 [=Liobunum intermediumR23] Prionostemma incertae sedis: *P. coronatum (Loman 1902) [=*Prionomma coronatum]C92 P. albimanum Roewer 1912R23 P. albipalpe (Banks 1898) [=Liobunum albipalpe]R23 P. albofasciatum (Cambridge 1901) [=Liobunum albofasciatum]R23 P. atrorubrum Roewer 1912R23 P. aureomaculatum Soares 1970KP-R02 P. aureum Roewer 1928KP-R02 P. bicolor Pocock 1903R23 P. bicoloripes Roewer 1933R33 P. bidens Roewer 1953KP-R02 P. biolleyi (Banks 1909) [=Liobunum biolleyi]R23 P. circulatum Roewer 1914R23 P. coriaceum (Cambridge 1904) [=Liobunum coriaceum]GG42b P. coxale (Banks 1909) [=Liobunum coxale]R23 P. dentatum Roewer 1910R23 P. duplex Chamberlin 1925GG42b P. farinosum Mello-Leitão 1938T-D03 P. festaiM-L32 P. fichteri Goodnight & Goodnight 1947GG47 P. foveolatum (Cambridge 1904) [=Leiobunum foveolatum]GG43 P. frontale (Banks 1909) [=Liobunum frontale]R23 P. fulvibrunneum Roewer 1928KP-R02 P. fuscamaculata Goodnight & Goodnight 1947GG47 P. genufuscum Roewer 1910R10 P. iguassuensis Mello-Leitão 1935T-D04 P. insculptum Pocock 1903R23 P. laterale (Banks 1909) [=Liobunum laterale]R23 P. limbatum Roewer 1953T-D04 P. lubeca Goodnight & Goodnight 1946GG53 P. magnificum Roewer 1953KP-R02 P. minimum Roewer 1910T-D03 P. nevermanni Roewer 1933R33 P. nigrum Roewer 1910R23 P. panama Goodnight & Goodnight 1942GG42b P. perlucidum Roewer 1910R23 P. pulchra Goodnight & Goodnight 1942GG42a P. reticulatum Roewer 1910GG42a P. richteri Roewer 1953KP-R02 P. riveti Roewer 1914R23 P. scintillans Pocock 1903R23 P. simplex Chamberlin 1925GG42b P. transversale Roewer 1953KP-R02 P. tristani (Banks 1909) [=Liobunum tristani]R23 P. victoriae Goodnight & Goodnight 1946GG53 P. vittatum Roewer 1910R23 P. wagneri Goodnight & Goodnight 1944GG44
*Type species of generic name indicated
References
[C92] Crawford, R. L. 1992. Catalogue of the genera and type species of the harvestman superfamily Phalangioidea (Arachnida). Burke Museum Contributions in Anthropology and Natural History 8: 1–60.
[GG42a] Goodnight, C. J., & M. L. Goodnight. 1942a. Phalangids from British Guiana. American Museum Novitates 1167: 1–13.
[GG42b] Goodnight, C. J., & M. L. Goodnight. 1942b. Phalangida from Barro Colorado Island, Canal Zone. American Museum Novitates 1198: 1–18.
[GG44] Goodnight, C. J., & M. L. Goodnight. 1944. More Phalangida from Mexico. American Museum Novitates 1249: 1–13.
[GG47] Goodnight, C. J., & M. L. Goodnight. 1947. Studies of the phalangid fauna of Central America. American Museum Novitates 1340: 1–21.
[GG53] Goodnight, C. J., & M. L. Goodnight. 1953. The opilionid fauna of Chiapas, Mexico, and adjacent areas (Arachnoidea, Opiliones). American Museum Novitates 1610: 1–81.
[HT12] Hedin, M., N. Tsurusaki, R. Macías-Ordóñez & J. W. Shultz. 2012. Molecular systematics of sclerosomatid harvestmen (Opiliones, Phalangioidea, Sclerosomatidae): geography is better than taxonomy in predicting phylogeny. Molecular Phylogenetics and Evolution 62 (1): 224–236.
[KP-R02] Kury, A. B., & R. Pinto-da-Rocha. 2002. Opiliones. In: Adis, J. (ed.) Amazonian Arachnida and Myriapoda pp. 345–362. Pensoft: Sofia.
[M-L32] Mello-Leitão, C. F. de. 1932. Opiliões do Brasil. Revista do Museu Paulista 17 (2): 1–505, 61 pls.
[R10] Roewer, C.-F. 1910. Revision der Opiliones Plagiostethi (=Opiliones Palpatores). I. Teil: Familie der Phalangiidae. (Subfamilien: Gagrellini, Liobunini, Leptobunini). Abhandlungen aus dem Gebiete der Naturwissenschaften, herausgegeben vom Naturwissenschaftlichen Verein in Hamburg 19 (4): 1–294.
[R23] Roewer, C.-F. 1923. Die Weberknechte der Erde: Systematische Bearbeitung der bisher bekannnten Opiliones. Gustav Fischer: Jena.
[R33] Roewer, C. F. 1933. Ergebnisse der Österreichischen Biologischen Costa-Rica-Expedition 1930. IV. Teil. Opilioniden. Annalen des Naturhistorischen Museum in Wien. Serie B. Botanik und Zoologie 46: 275–295.
[T-D03] Tourinho-Davis, A. L. 2003. On the dubious identity of Bastioides Mello-Leitão, 1931 (Eupnoi, Sclerosomatidae, Gagrellinae). Revista Ibérica de Aracnología 7: 241–245.
[T-D04] Tourinho-Davis, A. L. 2004. A new genus of Gagrellinae from Brazil, with a comparative study of some of the subtropical and southernmost tropical South American genera (Opiliones, Eupnoi, Sclerosomatidae). Revista Ibérica de Aracnología 9: 157–177.