On April 16 I was birding on the slopes of Phan Xi Pang mountain at approximately 2000m asl. We were in a little valley in open terrain, with marshy ground traversed by a few clear small streams. When checking one of the streams I noticed a huge dragonfly that was stuck in the grass, apparently freshly emerged. Its abdomen was bent sideways and it seemed not to be able to fly. In fact it missed the left hindwing.
It was immediately obvious that this was a Goldenring of some sort. Its massive size (97mm, HW 56mm) and the lack of anal triangle in the hindwing pointed me to Anotogaster. It is very similar to Anotogaster sieboldii, but there are some minor differences. Wilson (2005) already pointed out the occurrence of A. sieboldii in Guangxi Province in China and the differences between specimens there and the ones in Japan, but also why he considered them conspecific. My first impression of the appendages was that this also appeared to be A. sieboldii. However, Karube (2012) described 5 species for Vietnam, all also occurring in the Sapa region.
It is clear my specimen belongs to the sakaii-group of Anotogaster, if only based on the orange-brown mandibles, without yellow base. The other species in that group, A. chaoi, has slightly different measurements, notably HW and pterostigmata. It does have a brown antefrons, like my specimen, but I consider this caused by the general stage of the specimen, like other parts of its body that will still darken further.
|Anotogaster sakaii, male, as I found it with damaged abdomen|
|The same insect, showing more obviously the yellow wing bases.|
|Although clear yellow on postclypeus, the mandibles are orange-brown, without any yellow on the bases.|
|Hindwing showing the absence of the anal triangle, hence it is Anotogaster|
|Dorsal view of the appendages. The bent tips are curved upward and inward, maybe due to pressure from the ground upon which it rested. At the base, best visible in the top cercus in the photo a small but clear tooth.|
|View showing the ridges at the apical corners of the lower appendage, which becomes thicker apically.|