Pseudogagrella

Pseudogagrella nigridorsa, copyright 花跳.

Belongs within: Sclerosomatidae.

Pseudogagrella: a harvestman torn
Published 30 November 2019

The Sclerosomatidae are one of the most diverse of the currently recognised harvestmen families, and one of the most problematic when it comes to classification. In various earlier posts, I have noted the challenges that bedevil sclerosomatid systematics, many reflecting a historical focus on superficial external features of questionable evolutionary significance. Perhaps no taxon more neatly exemplifies the problems with higher sclerosomatid classification than the eastern Asian genus Pseudogagrella.

Pseudogagrella sakishimensis, copyright Tomoya Suzuki.

Historically, the greater number of sclerosomatids have been divided between two major subfamilies, the Leiobuninae and Gagrellinae. The Leiobuninae have mostly been recognised as living in the northern temperate regions whereas the Gagrellinae were mostly tropical. The division between the two subfamilies has long been regarded as more than a little fuzzy, and has usually hinged on a single feature: the presence (Gagrellinae) or absence (Leiobuninae) of rings of flexible integument (noduli) in the femora of the legs. Pseudogagrella is a genus of sclerosomatid harvestmen recognised from Japan, Taiwan, China and Sumatra (Chen & Shih 2017). Members of this genus lack leg noduli so have historically been included in the Leiobuninae. The problem is that their overall appearance, with a tendency to bold coloration, a tall median spine rising from the hardened scute covering most of the abdomen, and legs that are not merely long but ludicrously so (even by harvestman standards), is extremely similar to species of Gagrellinae. So much so, in fact, that some species currently placed in Pseudogagrella were long included in the archetypical gagrelline genus, Gagrella (Suzuki 1977).

With the distinction between the two subfamilies being so vague, I don’t think it really came as that much surprise to anyone when molecular phylogenetics underlined the need for a thorough re-working of sclerosomatid systematics. Though the analysis conducted by Hedin et al. (2012) did not support the prior distinction between ‘leiobunines’ and ‘gagrellines’, it did suggest the existence of distinct lineages occupying distinct geographical regions. One species of Pseudogagrella included in the analysis (the southern Japanese P. amamiana) was placed in a cluster of eastern Asian species including other Asian ‘gagrellines’, but also the ‘leiobunine’ ‘Leiobunum’ japonicum. So it seems likely that, should subfamilies of Sclerosomatidae continue to be recognised, Pseudogagrella will indeed be a member of Gagrellinae, but Gagrellinae itself shall not quite be what people think of it as being.

Pseudogagrella dorsomaculata, copyright Tyus Ma.

There is also, of course, the question of whether Pseudogagrella itself is a coherent unit. Hedin et al. (2012) included only the one Pseudogagrella species in their analysis and the need for an extensive revision of the Asian sclerosomatid genera still remains. A study of Chinese species assigned to the genus Melanopa (Zhang & Zhang 2013), which is primarily distinguished from Gagrella by having relatively shorter legs, suggested the possibility of this ‘genus’ being divided between groups of Palaearctic and Indo-Malayan species, and I’ve wondered if this division might carry further (unfortunately, I’m not aware of any Indo-Malayan ‘gagrellines’ being included in molecular phylogenies; I think all the Asian species covered by Hedin et al. were Palaearctic). The majority of Pseudogagrella species, found in Japan and Taiwan, can be comfortably compared to other sclerosomatids from that region, but the Sumatran P. multimaculata, and possibly the southern Chinese species, might turn out to be closer to their own geographical peers. As always, a great deal of research remains to be done.

Systematics of Pseudogagrella
<==Pseudogagrella Redikorzev 1936 [incl. Argyraster Nakatsudi 1942; Argyrasterinae]C92
| i. s.: P. amamiana (Nakatsudi 1942)S73 [=*Argyraster amamianusC92, A. amamianaC92]
| P. sakishimensis Suzuki 1971S73
| P. splendens (With 1903) (see below for synonymy)S77
| P. wangi Roewer 1957CS17
|--+--*P. sinensis Redikorzev 1936C92, CS17, C92
| |--P. chekiangensis Wang 1941CS17, W53
| |--P. minuta Roewer 1957CS17
| |--P. multimaculata Roewer 1957CS17
| |--P. pingi Wang 1941CS17, W53
| `--P. similis Wang 1941CS17, W53
`--+--+--P. andoi Suzuki 1977CS17, S77
| `--P. nigridorsa Chen & Shih 2017CS17
`--+--+--P. arishana Suzuki 1977CS17, S77
| `--P. sauteri Chen & Shih 2017CS17
`--+--P. taiwana Suzuki 1977CS17, T91
`--+--P. cyanea (Roewer 1915)CS17, T91 (see below for synonymy)
`--P. dorsomaculata Chen & Shih 2017CS17

Pseudogagrella cyanea (Roewer 1915)CS17, T91 [=Gagrella cyaneaT91; incl. G. formosae Roewer 1915T91, Pseudogagrella formosaeT91]

Pseudogagrella splendens (With 1903) [=Gagrella splendens; incl. G. splendens bispinosa Roewer 1910 non G. feae bispinosa Thorell 1889]S77

*Type species of generic name indicated

References

[CS17] Chen, S.-L., & H.-T. Shih. 2017. Descriptions of three new species of the harvestmen genus Pseudogagrella (Opiliones: Sclerosomatidae: Gagrellinae) from Taiwan, supported by morphological and molecular evidence. Zootaxa 4268 (1): 34–52.

[C92] Crawford, R. L. 1992. Catalogue of the genera and type species of the harvestman superfamily Phalangioidea (Arachnida). Burke Museum Contributions in Anthropology and Natural History 8: 1–60.

Hedin, M., N. Tsurusaki, R. Macías-Ordóñez & J. W. Shultz. 2012. Molecular systematics of sclerosomatid harvestmen (Opiliones, Phalangioidea, Sclerosomatidae): geography is better than taxonomy in predicting phylogeny. Molecular Phylogenetics and Evolution 62 (1): 224–236.

[S73] Suzuki, S. 1973. Opiliones from the South-west Islands, Japan. Journal of Science of the Hiroshima University, Series B, Division 1 (Zoology) 24: 205–279.

[S77] Suzuki, S. 1977. Opiliones from Taiwan (Arachnida). Journal of Science of the Hiroshima University, Series B, Division 1 (Zoology) 27 (1): 121–157.

[T91] Tsurusaki, N. 1991. Some harvestmen (Arachnida, Opiliones) from Taiwan. I. Phalangiidae, Leiobuninae. Zoological Science 8: 179–185.

[W53] Wang F.-C. 1953. A list of Chinese spiders of the order Opiliones. Kunchong Xuebao [Acta Entomologica Sinica] 3: 503–512.

Zhang, C., & F. Zhang. 2013. Notes on some species of the genus Melanopa (Opiliones: Sclerosomatidae: Gagrellinae) from China, with description of a new species. Journal of Arachnology 41: 306–318.

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