Sunday, 24 August 2014

Aciagrion approximans - no end to my problems*

*Adjusted on April 16, 2016, after communication with Oleg Kosterin. A. approximans has now been redescribed and takes precedence over A. tillyardi.

When checking for the umpteenth time the small pond next to the lodge in Cat Tien I noticed a small coenagrionid in the grass, freshly emerged. Although small and fresh damsels will not likely survive capture, it was clear this was something I had not seen before, so I decided to catch it and stick it under a glass in my room to harden. I am sort of glad I did, for when later checking the details, it became clear this was a small Aciagrion species with a concave posterior margin to the superior appendages. Sort of glad, as this is where the problems begin. As can be seen from the photos on Asia-Dragonfly and the discussion on the website of Dennis for Thailand, there are several species that are being claimed as A. tillyardi, the species that would be the species of choice for this little fellow. There are only a few Aciagrion with forked superior appendages. The larger A. migratum occurs in Vietnam too. Now, there is a purplish Aciagrion that occurs in Thailand, for instance, with elongate postocular spots connected by a bar across the occiput, so the complete feature is like one elongate bar across the dorsum of the head. And there is a blue species with rounder postocular spots. The appendages are apparently similar. Th original description of A. tillyardi in Laidlaw (1919) does not mention any purple tones, and nor does he mention blue for that matter. He speaks of narrow gray-blue ante-humeral bands (sic) and gray-olive sides. He does state that the head has "a linear gray-blue post-ocular mark on either side, joined by a fine transverse line of the same colour across the occiput." Not purple, but also no rounded postocular spots. He also states that segment 9-10 are gray-blue and S10 black, obviously a mistake. I assume he means that 8-9 are gray-blue. One wonders whether this description fits any of the species claimed to be A. tillyardi. Luckily, my specimen is teneral and therefore neither blue nor purple, but it does have elongate postocular markings. For the time being I claim this as A. tillyardi. It certainly is not any of the other species in the area.

The fresh tiny male Aciagrion approximans

Dorsal view of appendages
Dorso-lateral view of appendages
Dorsal view of head, showing elongate postocular markings, blacking prothorax (but blue frontal lobe) and blueish antehumerals, but note this is a very fresh specimen.
And we wait for some courageous researcher willing to dive into this genus and sort things out. I also hope to collect mature specimens later this year. Like the genus Heteragrion in South-America and so many other examples, it might be better to just discard all old descriptions based on a few specimens, now long turned into dust, where these descriptions do not provide enough detail or decent drawings. Sorry for the scientists of yore, who clearly did what they could under the circumstances and based on what was seen as proper scientific work. Sadly, it does not stand the test of time. Sacrilege! Yes, but sometimes it may be necessary to throw of the shackles of past inadequacies.

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