Hesperonemastoma Gruber 1970

Introduction

The North American genus Hesperonemastoma shows strong morphological and ecological convergence with Nemastomatinae species in Europe, and had long been treated as such. Yet, defining characteristics of Ischyropsalidoidea are present, as well as the absence of clavate hairs and presence of bottlebrush hairs point to this superfamily. Herein it is easily defined by body form of nemastomatid habit, being globular, minute (1-2 mm) and often with rows of bridge-thorns, as well as exhibiting slender palps, moderate cheliceral size and short legs. Morphological peculiarities of the genus concern the chelicerae that lack glandular structures in males while such seem present on the femora of the palps in some species. The penis is short, often filled in its whole length by the single muscle and the penial glans is short and compact, set with strong spines and a short, often bent stylus (Gruber 1970). The distribution in North America is disjunct, with a continuous range along the western Coast from California to Canada, a second part in the Central to Northern Rocky Mountains and the third in the Appalachians. In the Southwest they are confined to higher altitudes.

Taxonomy and Discussion of Phylogenetic Relationships

Gruber (1970) established the genus and transferred it to Ischyropsalidoidea, studying limited material. He mentioned species borders drawn by his descriptions to not be definite. A revision is necessary to clarify species limits, as the outlined forms appear very heterogeneous. Genetic data supports Hesperonemastoma to be closely related to the apparently morphological distant genus Taracus (Giribet et al. 2010). Similarities can be seen in the absence of male cheliceral glands, the slender palps set with bottlebrush hairs and the genital morphology, which is relatively simple.

Ecology and Life History

Species of Hesperonemastoma are recorded from different forest communities where they can reach high abundances. They are mostly found under stones and logs but can also be sieved from leaf litter. Loose aggregations of up to 40 specimens have been found. One troglobiont species is known (Shear 2010).

References

Giribet, G., Vogt, L. Pérez-González, A., Sharma, P. 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. 1970. Die "Nemastoma"-Arten Nordamerikas (Ischyropsalididae, Opiliones, Arachnida). Annalen des Naturhistorischen Museums in Wien 74:129-144.

Shear, W. A. 2010. Hesperonemastoma smilax, n. sp., a remarkable new harvestman from a cave in West Virginia, with comments on other reported cave-dwelling Hesperonemastoma species (Opiliones, Ischyropsalidoidea, Sabaconidae). Journal of Cave and Karst Studies 72(2):105-110.