A new species of Sieboldius?*

*Adjusted April 1, 2016. Late March I received photos from the holotype of S. nigricolor from Ben Price, curator at the British Natural History Museum. Clearly my species is that species. The drawings in Fraser (1924) are just pretty bad, that is all. The inferior appendage is not at all rounded, but squarely hollowed out. This species is known fro just a few scattered sites in Myanmar, Lao DPR and northern Thailand. But clearly also occurs in Vietnam.

There are 8 species described for the genus Sieboldius, closely related to Hagenius of Northern America. One interesting aspects of the species in this genus is that S. japponicus in spite of its name ranges in Borneo, not in Japan, where the related S. deflexus occurs. 5 species are known from China. Apart from the aforementioned S. deflexus, these are S. albardae, S. alexanderi, S. maai, and S. herculeus. In South-East Asia two more species occur, the aforementioned S. japponicus and S. nigricolor. An enigmatic species is S. gigas. This species is the only one described for Vietnam (Martin 1904, "Tonkin") from a single specimen and never seen again.

It was very exciting that I encountered several Sieboldius specimens in Cao Bang Province. On June 25 I was able to take some pictures of a Sieboldius perched on top of a rock in a mountain stream. On the photos relatively long superior appendages were visible, leading me to the assumption it might be S. alexanderi. On 7 July I was able to catch a male at the same spot. This male had distorted appendages on one side, but the good side showed appendages that were different from S. alexanderi. Was it then the more common S. deflexus? Wen-Chi Yeh provided me with conclusive evidence to the contrary. In fact, especially the lower appendage was clearly different from all known species. Could this be the enigmatic S. gigas, the stuff of legends? In fact, as the name reflects, this species would be gigantic, with an abdomen of 71mm. The description otherwise is very poor, but if we believe the size to be correct, this can hardly be the present species, which has abdomen length of 56mm. Finding S. gigas would be something like finding Echo maxima, but if we consider the poor description to be correct, then the mystery remains unsolved. However, in that case this must be an as yet undescribed species of Sieboldius! Work to do.

Sieboldius nigricolor, on a rock in the sun

Another male in hand, a stunning beast, but proportionally weird with its small head and long legs

Appendages of Sieboldius nigricolor in ventral view

And in dorsal view