Parariukiaria, Nguyen, Anh D., 2016

Nguyen, Anh D., 2016, Discovery of a new millipede species in northern Vietnam, and the proposal of a new genus, Parariukiaria (Diplopoda, Polydesmida, Xystodesmidae), Zootaxa 4121 (3), pp. 331-336 : 332

Genus Parariukiaria gen. nov.

Type species. Parariukiaria cucfuongensis sp. nov., by original designation

Diagnosis. A xystodesmid genus characterized by leg prefemora with/without ventral processes; gonopod coxa without proximal apophysis, and with/without a macroseta; if present, prefemoral process extremely short, triangular or curved spiniform/tubercle; acropodite very long and slender, somewhat flagelliform; strongly curved or helicoid distally; demarcation between gonopod prefemur and femur absent.

The new genus is fairly close to two genera, Riukiaria Attems, 1938 and Xystodesmus Cook, 1895 found in Japan, Taiwan and recently China. However, it clearly differs from Riukiaria in the prefemoral process being strongly reduced as a short, triangular tubercle/spine, and not forming a forceps with the long and slender acropodite. On the other hand, Riukiaria has a biramous, forceps-like gonopod conformation; gonopod coxa with a macroseta, acropodite thick and slightly longer than or subequal to prefemoral process, and leg prefemora with ventral processes.

The genus Xystodesmus may be distinguished from the new genus by its gonopod conformation being more elaborate, with a well-developed prefemoral process; a deep division between the acropodite and prefemoral process, but these often subequal in length; gonopod coxa always with a macroseta, but with or without coxal apophysis. On the contrary, Parariukiaria species have a long and slender acropodite; if present, the prefemoral process is very short; gonopod coxa with or without a macroseta; coxal apophysis absent.

The new genus is also different from the genus Koreoaria Verhoeff, 1937 in having the prefemoral process much shorter, and the acropodite simple, flagelliform.

Etymology. The gender is feminine. The genus is named after its similarity to the genus Riukiaria .

Remarks. Recently, Golovatch (2014) described five new Riukiaria species from Sichuan Province ( China). Of his five new species, two clearly fit well into the genus Riukiaria with forceps-like gonopod conformation, Riukiaria martensi Golovatch, 2014 and R. davidiani Golovatch, 2014 . The other three species, R. belousovi Golovatch, 2014 , R. korolevi Golovatch, 2014 , and R. kabaki Golovatch, 2014 , seem not belong to the genus Riukiaria because the prefemoral process is strongly reduced, even totally missing, and the solenomere is long and slender, acuminating towards tip.

According to Tanabe & Shinohara (1996) and Korsós et al. (2011), the genus Riukiaria is typically characterized by the forceps-like gonopod conformation, in which a thick acropodite is subequal to or slightly longer than prefemoral process. In other words, the prefemoral process is always well-developed. Tanabe & Shinohara (1996) also stated that the gonopods of Riukiaria are relatively stable within the genus. It means that the strongly reduced, even missing, prefemoral process could not be a diagnosic character for the genus Riukiaria ; it could be for another taxon.

Comparing the three genera, Riukiaria , Xystodesmus and Parariukiaria , a modification trend can be seen in the gonopod prefemoral process and acropodite. While both Riukiaria and Xystodesmus have well developed prefemoral processes and a thick acropodite, Parariukiaria is totally different with strongly reduced prefemoral processes and slender acropodites. The relationship among three genera has not yet been resolved, but we can hypothesize that Parariukiaria might be evolved from the genus Riukiaria when it moved eastwards and southwards through Asia. During the movement, the gonopod prefemoral process has been reduced. However, it is more data is needed, especially molecular data for phylogenetic analysis among the three genera.