Crosbycus Roewer, 1914 - Crosbycus dasycnemus (Crosby, 1911)
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, and 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). Along with Hesperonemastoma Crosbycus has been transferred to the new family Taracidae, while this placement requires confirmation for the character-poor Crosbycus (Schönhofer 2013).
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 considered invalid till they can be assigned to a distinct species within the Nemastomatidae (Schönhofer 2013).
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.
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.
Schönhofer, A.L. 2013. A taxonomic catalogue of the Dyspnoi Hansen and Sørensen, 1904 (Arachnida: Opiliones). Zootaxa 3679 (1): 1-68.
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.
Credits
Page created by Axel L. Schönhofer. Dave Carlson helped improve the English.
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, and 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). Along with Hesperonemastoma Crosbycus has been transferred to the new family Taracidae, while this placement requires confirmation for the character-poor Crosbycus (Schönhofer 2013).
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 considered invalid till they can be assigned to a distinct species within the Nemastomatidae (Schönhofer 2013).
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.
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.
Schönhofer, A.L. 2013. A taxonomic catalogue of the Dyspnoi Hansen and Sørensen, 1904 (Arachnida: Opiliones). Zootaxa 3679 (1): 1-68.
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.
Credits
Page created by Axel L. Schönhofer. Dave Carlson helped improve the English.
