Taxonomic revision of the dwarf spider genus Shaanxinus Tanasevitch, 2006 (Araneae, Linyphiidae, Erigoninae), with new species from Taiwan and Vietnam

Abstract

Dwarf spiders are of special interest due to their sexually dimorphic prosomal structures in males. Glandular secretions within these structures serve as nuptial gifts, and thus sexual selection may have contributed to their high species richness. However, species diversity of dwarf spiders in East Asia is yet understudied. Here, we review the erigonine genus Shaanxinus Tanasevitch, 2006, and describe 13 new species from Taiwan: S. magniclypeus sp. n. (♂♀), S. shihchoensis sp. n. (♂♀), S. shoukaensis sp. n. (♂♀), S. hirticephalus sp. n. (♂♀), S. mingchihensis sp. n. (♂♀), S. makauyensis sp. n. (♂♀), S. lixiangae sp. n. (♂♀), S. curviductus sp. n. (♂♀), S. tsou sp. n. (♂♀), S. hehuanensis sp. n. (♂♀), S. seediq sp. n. (♂♀), S. meifengensis sp. n. (♂♀), and S. atayal sp. n. (♂♀). In addition, one new species from Vietnam, S. tamdaoensis sp. n. (♂), is described from museum material. We reconstructed the dimension of glandular tissues associated with male prosoma modifications in Shaanxinus, as well as the detailed palpal structure by micro-computer tomography. Placement within Shaanxinus and intrageneric relationships were inferred by means of a cladistic analysis based on morphological characters. Sequences of COI, 16S, and 28S genetic markers corroborated the monophyly of some species, as well as male-female matching. Poly-/paraphyly of morphologically delimitated species in the mitochondrial DNA (mtDNA) trees led to the discovery of two seemingly identical species, for which diagnostic morphological features could then be further identified. We discuss incomplete lineage sorting and introgression as possible causes of mtDNA poly-/paraphyly in morphologically indistinguishable specimens.