Crosbycus dasycnemus (Crosby 1911) Roewer 1914

Introduction

Crosbycus represents minute long-legged animals of less than 1 mm in body size. They inhabit humid microhabitats in forests and are assumed to be mainly parthenogenetic, as males are rarely recorded (Gruber 2007). Despite its minute size, the single accepted species C. dasycnemus (Crosby 1911) shows a disjunct distribution covering a large area in eastern North America (Shear 1986) and smaller areas in China (Tsurusaki & Song 1993) and Japan (Suzuki 1972).

Taxonomy and Discussion of Phylogenetic Relationships

The type species Nemastoma dasycnemum was transferred to Ischyropsalidoidea by Martens (1976). The family assignment of Crosbycus still remains questionable, but Shear (1986) proposed closest relationship to Hesperonemastoma which agrees with the slender palps set with bottlebrush hairs and with the overall structure of male genitalia presented by Gruber (2007). However, Hesperonemastoma has been transferred to Sabaconidae.

Gruber & Martens (1968) stated all European species of Crosbycus to represent juveniles of Nemastomatidae, and as adults of Crosbycus have never been collected in Europe, all Crosbycus species cited for Europe have to be considered invalid. Several Crosbycus have already been synonymized with Mitostoma and Paranemastoma. The remaining names are listed below due to uncertainty assigning them to a distinct species within the Nemastomatidae. According to drawings and body size the species C. cavernae and C. speluncarum can be assigned to Paranemastoma, probably C. goodnighti as well (all Roewer 1951).

On the other hand, the amphipacific populations of Crosbycus probably warrant species status, difficult to establish on morphology alone as many somatic characters are reduced in this minute animals and male specific characters are largely unavailable.

• invalid: Crosbycus goodnighti Roewer, 1951:151
• invalid: Crosbycus graecus Giltay, 1933:3
• invalid: Crosbycus pentelicus Roewer, 1951:152
• invalid: Crosbycus speluncarum Roewer, 1951:152

References

Gruber, J. 2007. Ceratolasmatidae. In: Pinto-da-Rocha, R., Machado, G. and G. Giribet. (eds.), Harvestmen: the biology of Opiliones. Harvard University Press, Cambridge: 136-142.

Gruber, J. and J. Martens. 1968. Morphologie, Systematik und Ökologie der Gattung Nemastoma C. L. Koch (s.str.) (Opiliones, Nemastomatidae). Senckenbergiana biologica 49:137-172.

Martens, J. 1976. Genitalmorphologie, System und Phylogenie der Weberknechte (Arachnida: Opiliones). Entomologica Germanica 3(1/2):51-68.

Roewer, C.F. 1951. Über Nemastomatiden. Weitere Weberknechte XVI. Senckenbergiana 32(1/4):95-153.

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.

Suzuki, S. 1972. On the discontinuous distribution in some Opiliones. Acta arachnologica 24(1):1-8.

Tsurusaki, N. and D. Song. 1993. Occurrence of Crosbycus dasycnemus (Crosby) (Opiliones, Palpatores, Ceratolasmatidae) in China. Japanese Journal of Entomology 61(1):175-176.