Sunday, 20 July 2014

Merogomphus, Anisogomphus and Euthygomphus* **

*Updated on June 1, 2016 after publication of Anisogomphus neptunus
**Updates on December 15, 2016 after publication of the genus Euthygomphus Kosterin, 2016

There is one species of Merogomphus known from Vietnam. Merogomphus pavici is a large species, with distinctive appendages and markings. Euthygomphus parvus is a small southern species recorded from southern Vietnam that formerly was also included in Merogomphus. Then there is Anisogomphus tamdaoensis, described from Tam Dao, but at least also present at Ba Vi NP and in Hoa Binh Province and also originally included in Merogomphus.

During our travels at the end of June and beginning of July we observed Merogomphus pavici in Phu Tho Province (Xuan Son NP), in northern Bac Kan Province and in southern Cao Bang Province. This comes as no surprise, it is a widespread species.

Merogomphus pavici, male, from Bac Kan Province. Long legs indeed.
Another species we encountered was Anisogomphus tamdaoensis. A male was observed in Hoa Binh Province at Cuu Thac - Tu Son and what is very likely the female of this species was caught freshly emerged in Pia Oac Nature Reserve. It is safe to conclude that this species is much more widely spread than the rather restricted range of Tam Dao and Ba Vi.

Male Anisogomphus tamdaoensis from Hoa Binh Province, June 27
And its distinctive appendages in dorsal view

Female of presumably Anisogomphus tamdaoensis from Pia Oac, June 23.
However, now things get a little more complicated. In northern Bac Kan Province (and on June 28 also in Lang Son Province) we encountered several smallish male gomphids that at first glance seemed Euthygomphus parvus. Even at a second glance they did. It was only at a much later stage (today) that I realized they were in fact something else, namely Euthygomphus koxingai, a species known from southern China of which its occurrence in northern Vietnam is not at all surprising. It is uncannily close in outward appearance to E. parvus, which has a different penile organ. Also, in that species the antehumeral stripes are confluent with the collar. The appendages appear identical (see for instance the entry on E. parvus in the blog of Dennis Farrell). In his table of Anisogomphus Zhao (1990) uses the all black labrum of A. koxingai to distinguish it from other species, but as Wilson has pointed out, mainland China A. koxingai has in fact transverse yellow marks on the labrum (at the time of publication of their articles this species was still included in Anisogomphus).

Euthygomphus koxingai, male, late June Bac Kan Province

Another male Euthygomphus koxingai in the field

Appendages in dorsal view

In lateral view

And in ventral view
And finally, in Pia Oac I observed many Anisogomphus females that came to drop balls of eggs, almost always at the very same location and sometimes several females at the same time. They all came to a little sandy shallow area right under a rock, would drop eggs, fly up to perch on a nearby fern and produce another egg-ball to fly down and dip it and so on. These all shared extensive yellow both dorsally and laterally on the abdomen. They also had rather long vulvar lamina. I noticed photos on the web of seemingly identical female Anisogomphus from Thailand. Wilson (2005) mentions an Anisogomphus sp female from Guangxi that may also be closely related. For now, I can only treat this as Anisogomphus sp, unless anyone recognizes the species or until we can find a male. Strangely, although at least 20 females came to oviposit over the days I was in Pia Oac, no male was ever seen.
Female Anisogomphus neptunus in hand, Pia Oac Nature Reserve, early July

Another female preparing egg ball, this time not on a fern, but perched on a rock.

Close-up of abdomen, showing the extensive amount of yellow, both dorsally and laterally

Close-up of vulvar lamina

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