Nemastoma bidentatum Roewer, 1914

Novak, Tone, Novak, Ljuba Slana, Kozel, Peter, Schaider, Miriam Gudrun, Komposch, Christian, Lipovšek, Saška, Podlesnik, Jan, Paušič, Igor & Raspotnig, Günther, 2021, Hidden diversity within the Nemastoma bidentatum Roewer, 1914 complex (Opiliones: Nemastomatidae) Part I: Morphological evidence, European Journal of Taxonomy 777, pp. 1-67 : 7-8

Nemastoma bidentatum Roewer, 1914 complex

Diagnosis

Uniformly black subspecies of Nemastoma bidentatum and closely related species, with glans with two pairs of lateral lancet-like, articulated spines, and saw-like series of denticles on Fe IV.

Morphology

The Pe is characterized by a bulbous, muscular, posteriorly medially split basis, a thin truncus and triangular glans, eventually with a shoulder-like truncated tip, either slightly narrower, evenly wide or slightly wider than the truncus, with two pairs of lateral lancet-like, articulated spines. The distal part of the glans is characteristic of some taxa. The shape and size of the Ch basal article and especially of Ch- Apo, and the shape, size and armament of Pa-Fe, and in some taxa Pa-Ti, are further diagnostic characters. Other characters, such as the Pa and leg lengths, may support identification, but are not definitively distinctive. The identification key includes both sexes in the nine pure taxa known to date, except the unknown female of N. pluridentatum stat. nov., and typical male hybrids.

Remarks

To date, four additional taxa of the N. bidentatum complex have been discovered in Slovenia: N. b. gruberi Novak, Slana Novak, Kozel & Raspotnig ssp. nov., N. b. martensi Novak, Slana Novak & Raspotnig ssp. nov., N. b. schmidti Novak, Raspotnig & Slana Novak ssp. nov. and N. b. sneznikensis Novak, Komposch, Slana Novak & Raspotnig ssp. nov., and one in Bosnia and Herzegovina: N. kozari Novak, Kozel, Podlesnik & Raspotnig sp. nov. Within these new taxa, the relatively consistent external morphology of the male Ch-Apo, Pa and glans allows reliable assignment of most individuals. However, N. b. gruberi ssp. nov. shows considerable variation in morphology, especially in the Pa-Fe armament, which in some particular cases still raises doubts about the reliability of the assignment (see the description of the taxon for more details). This is because we are still missing a broad review of potentially syntopic hybrids that should be based on data sets independent from morphology, e.g., chemical characters from highly specific scent gland secretions. Such individuals arise from some marginal localities of the area, e.g., from the very south-west of Slovenia, where we still have not been able to exclude the eventual existence of hybrids with N. b. schmidti ssp. nov. Morphological differences between females based on the Ch, Pa and Rec sem characters are less conspicuous, but allow correct identification of over 90% of individuals belonging to pure subspecies. Besides, a pairwise vicariance in most neighboring subspecies reveals their different ecological requirements, resulting in niche partitioning. On the other hand, hybrids in the contact zones of adjacent populations of some taxa reveal active gene exchange, supporting the subspecies status of these taxa. Nemastoma bidentatum in Austria deserves a separate treatise, while scarce records from the Balkan countries do not allow any further conclusion for the time being.

Thus, to date, there are four species in the Nemastoma b. complex in total: Nemastoma bidentatum Roewer, 1914 , N. relictum Gruber & Martens, 1968 stat. nov. and N. pluridentatum (Hadži, 1973) stat. nov., both raised to the species level, and the newly discovered N. kozari Novak, Kozel, Podlesnik & Raspotnig sp. nov.