Unexpectedly high number of 18S rRNA gene clusters in Miopsalis dillyi (Opiliones: Cyphophthalmi: Stylocellidae) from Mindanao, Philippines

The suborder Cyphophthalmi (Arachnida: Opiliones) is the sister group to all remaining harvestmen. The group typically shows limited dispersal abilities, cryptic diversity and long-isolated populations. These facts make the group interesting for biogeographic, phylogenetic and cytogenetic studies. The suborder is divided into six families, all of them with a specific and long evolutionary history. However, many species are still undescribed, and their cytogenetic data are only fragmentary. This fact complicates the reconstruction of the main mechanisms of karyotype evolution in this harvestmen suborder, and utilization of the cytogenetic markers in the taxonomy of this morphologically uniform group of arachnids. Here, we present a cytogenetic study of one species of Miopsalis Thorell, 1890, of the family Stylocellidae from Mindanao (Philippines). Its karyotype consisted of mainly biarmed chromosomes (2n ¼ 28). Interestingly, we found a multiplication of 18S rRNA gene clusters in up to seven pairs, which is one of the highest numbers in known harvestmen.
These results support the likely presence of distinctive karyotype variability in an additional cyphophthalmid family, Stylocellidae (2n ¼ 28–30).