Dyspnoi

Introduction

The Dyspnoi comprise about 330 species and are the second smallest suborder within Opiliones. Despite this small number of species, Dyspnoi taxa exhibit a high diversity of body forms, ornamentation and a variety of unique and bizarre eye mounds and associated features. Taxa include the largest opilionid in terms of body length, more than 23 mm in Trogulus torosus, and species below 1 mm, such as Crosbycus.

The high morphological heterogeneity makes it difficult to base definition and systematics of Dyspnoi on a reasonable number of shared morphological characters, especially as genital morphology is relatively simple and very similar in several unrelated groups. Despite this a few distinct morphological autapomorphies are shared throughout the group. Claws on the palps are missing, although sometimes a small peg like structure remains. Chelicerae are equipped with narrow, parallel, diaphanous teeth. These diaphanous teeth are lost in a few species with significantly enlarged chelicerae. It is interesting to note that elongate chelicerae evolved several times independently in Ischyropsalis, Nipponopsalis and Taracus. Dyspnoi show a disjunct Holarctic distribution with centers of generic endemism in the Western Palearctic and the Nearctic.

Discussion of Phylogenetic Relationships

The Dyspnoi have been accepted as monophyletic since Hansen and Soerensen (1904), and supported with modern approaches based on cladistics and molecular data (Shultz 1998, Giribet et al. 2010). However, there is no general consensus regarding the internal phylogenetic structuring of Dyspnoi (for a detailed overview see Gruber 2007a). Phylogenetic results based on DNA sequence data appear preliminary because of incomplete taxon sampling (Giribet et al. 2010). The North American genera of Ischyropsalididae are particularly hard to place within an existing taxonomic framework.

Recent revisions (Martens 2006, Schönhofer and Martens 2008, 2009, Shear 2010) indicate that the number of taxa in some groups, especially the character delimited Trogulidae, are underestimated due to cryptic species diversity. The same holds probably true for North American Hesperonemastoma, Taracus, the genus Sabacon and several groups within the European Nemastomatidae. Conversely, the number of valid taxa may significantly decrease when taxonomic synonymies within the specious European Nemastomatidae, especially within Nemastoma s.l. and Paranemastoma are resolved.

Ecology and Life History

The majority of Dyspnoi taxa prefer humid and temperature-stable microhabitats and show low dispersal abilities, making them excellent candidates for biogeographic studies. Several groups frequently enter caves and feature troglobionts. Predatory specialists, especially snail-eaters, are known in Trogulidae and Ischyropsalididae. Nemastomatidae and Sabaconidae have complex hairs on the palps that are probably used to catch or glue small arthropods or even aquatic insects from the water surface.

References

Giribet, G., L. Vogt, A. Pérez González, P. Sharma and A. B. Kury. 2010. A multilocus approach to harvestman (Arachnida: Opiliones) phylogeny with emphasis on biogeography and the systematics of Laniatores. Cladistics 26:408-437.

Gruber, J. 2007. Dyspnoi - Historical systematic synopsis. In: Pinto-da-Rocha, R., G. Machado, G. Giribet., eds. Harvestmen: the biology of Opiliones. Harvard University Press, Cambridge.

Martens, J. 2006. Weberknechte aus dem Kaukasus (Arachnida, Opiliones, Nemastomatidae) [Harvestmen from the Caucasus (Arachnida, Opiliones, Nemastomatidae)]. Senckenbergiana Biologica 86(2):145–210.

Shear, W. A. 1975. The opilionid genera Sabacon and Tomicomerus in America (Opiliones, Troguloidea, Ischyropsalidae). The Journal of Arachnol. 3:5–29.

Shear, W. A. 1986. A cladistic analysis of the opilionid superfamily Ischyropsalidoidea, with descriptions of the new family Ceratolasmatidae, the new genus Acuclavella, and four new species. American Museum Novitates 2844:1–29.

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.

Shear, W. A. and J. Gruber. 1983. The opilionid subfamily Ortholasmatinae (Opiliones, Troguloidea, Nemastomatidae). American Museum Novitates 2757:1–65.

Schönhofer, A. L. and J. Martens. 2008. Revision of the genus Trogulus Latreille: the Trogulus coriziformis species-group of the western Mediterranean (Opiliones: Trogulidae). Invertebrate Systematics 22(5):523–554.

Schönhofer, A. L. and J. Martens. 2009. Revision of the genus Trogulus Latreille: the Trogulus hirtus species-group (Opiliones: Trogulidae). In Kropf, C. & Horak, P. (eds). Towards a natural history of arthropods and other organisms. In memoriam Konrad Thaler. Contributions to Natural History 12:1143–1187.

Shultz, J. W. 1998. Phylogeny of Opiliones (Arachnida): an assessment of the "Cyphopalpatores" concept. The Journal of Arachnology, 26(3): 257-272.