Nemastomatidae Simon 1872

Introduction

Nemastomatidae represents the most diverse family of the Dyspnoi, contributing more than half the genera and about a third of the species. They are very small to medium sized harvestmen with a disjunct Holarctic distribution. The center of diversity is the Western Palearctic, where most genera and species of the Nemastomatinae occur that often reach high population densities. The subfamily is also present in Asia. The second subfamily, Ortholasmatinae, has the most described species in Central America and along the Western Coast of North America. Two species occur in isolated localities in Asia.

Prominent features of Nemastomatidae are the complex club-shaped hairs on the palps, whose function is still speculative (Wachmann 1970). These hairs can be found in juveniles of other Troguloidea, but in Nemastomatidae they are prominent in all stages of live. The translated scientific name “thread-mouth” likely refers to the palps being covered with these conspicuous hairs (Simon 1872). Other features of the family are unique male genital morphological traits within the Dyspnoi: unlike other Troguloidea, the glans is not movable against the truncus and the slender truncus cane is probably deformed as a whole when the muscles are contracted. The muscles are concentrated in the bulblike base of the penis and muscular tendons connect muscles and the distal part of the truncus (except for Mitostoma). The mechanical stress applied to the distal part of the penis leads to the development of exotic wing like stabilizing structures (Martens 2011, Schönhofer and Martens 2012). Many Nemastomatidae show rich and elaborate ornamentation of the dorsal body, with rows of spines, elevated cones, bridge-thorns and/or triangular intersecting thorns, forming distinct patterns that are species- or even group- specific.

Taxonomy and Discussion of Phylogenetic Relationships

Efforts to organize the diversity within Nemastomatidae started relatively late with Roewer (1951) and Kratochvíl (1958). Since then, taxonomy moved from applying exclusively external morphological characters towards an elaborate systematic interpreting male genital morphological functionalities and male cheliceral apophyses and glands (started by Šilhavý 1966, summarized in Schönhofer and Martens 2012). New genera and species are still described on a regular basis, suggesting research to be necessary in many geographic areas, especially in Asia (Martens 2006, Snegovaya 2010, Schönhofer and Martens 2012) and Central America (Shear 2006, 2010).

References

Kratochvíl, J. 1958. Höhlenweberknechte Bulgariens (Palpatores - Nemastomatidae). Práce Brněnské základny Československé akademie věd 30(12):523-576.

Martens, J. 2006. Weberknechte aus dem Kaukasus (Arachnida, Opiliones, Nemastomatidae), Senckenbergiana biologica 86(2):145-210.

Martens, J. 2011. The Centetostoma scabriculum complex - a group of three cryptic species (Arachnida: Opiliones: Nemastomatidae). Zootaxa 2783:35-51.

Roewer, C. F. 1951. Über Nemastomatiden. Weitere Weberknechte XVI. Senckenbergiana 32:95-153.

Schönhofer, A.L. and J. Martens. 2012. The enigmatic Alpine opilionid Saccarella schilleri gen. n., sp. n. (Arachnida: Nemastomatidae) - isolated systematic placement inferred from comparative genital morphology. Organisms Diversity and Evolution (online).

Shear, W. A. 2006. Martensolasma jocheni, a new genus and species of harvestman from Mexico (Opiliones: Nemastomatidae: Ortholasmatinae). Zootaxa 1325:191-198.

Shear, W. A. 2010. New species and records of ortholasmatine harvestmen from México, Honduras, and the western United States (Opiliones, Nemastomatidae, Ortholasmatinae). ZooKeys, 52:9-45.

Šilhavý, V. 1966. Über die Genitalmorphologie der Nemastomatidae (Arach., Opiliones). Senckenbergiana biologica 47:67-72.

Simon, E. 1872. Notices sur les arachnides cavernicoles et hypogés. Annales de la Société Entomologique de France 5(2):214-244.

Snegovaya, N. Y. 2005. New Harvestman Genus and Species from Kyrgyz Republic (Kyrgyzstan) (Arachnida: Opiliones: Nemastomatidae). Acta Zoologica Bulgarica 62(3):351-354.

Wachmann, E. 1970. Der Feinbau der sog. Kugelhaare der Fadenkanker (Opiliones, Nemastomatidae). Zeitschrift für Zellforschung 103:518-525.