Scalmogomphus revisited - a dream or a nightmare

Although late in the season for gomphids, we had our eyes open at the gold-diggers stream in Pia Oac this Saturday October 4 because the sun was out. Indeed, two male Scalmogomphus chased each other and then perched on the rocks. Catching them is a priority, as there is a mystery to be solved here: although I have not been able to find consistent differences in males between this location and Yen Bai, the females I caught here have very different vulvar lamina. But lucky for these males, I missed completely when trying to catch them. But a while later I noticed one of them, or another, who knows, perched on top of a bush nearby. I was able to catch it. Still carrying it in my hand, I went back to the stream and noticed another one. This seemed to be very much paler. I decided to try and net that one too and I was successful. As this second one was quite a bit lighter in coloration, I decided to take both home, scanning them would provide nice input on the extremes of variability in the species. So far so good.

Until yesterday evening under the microscope it became apparent that these two specimens are in fact different species, with rather great structural differences in their anal appendages to match the differences in coloration and size.

There has been quite a bit of confusion in the literature concerning some closely related genera in the Onychogomphids. Onychogomphus, Nychogomphus, Phaenandrogomphus and Scalmogomphus share many characteristics and species have been moved from one genus to another time and again. Chao (1990) erected Scalmogomphus for a new species, Scalmogomphus falcatus, on the basis of its peculiar penile organ. In fact, that organ also occurs in two other species that were described subsequently: S. guizhouensis (Zhou and Li, 2000) and S. weshanensis (Zhou, Zhou and Lu, 2005). Onychogomphus bistrigatus was also moved to this genus (Chao, 1990). If so, it is strange that O. schmidti, with a rather similar penile organ, has not yet been included, but remains in Onychogomphus. Onychogomphus dingavani was moved to Phaenandrogomphus by Chao. I have no knowledge of its penile organ, but this is another closely related species.

It is difficult to establish the differences in the literature between the three Chinese species of Scalmogomphus. Drawings are minimal in quality and my Chinese is extremely pour, not to say absent. There are few published photos of certain affiliation, and some on the web are clearly mistaken. It is unclear to me whether these species are true species, or whether, they just represent variants, a result of the few specimens concerned and the inherent intraspecific variability. It is simply hard to judge from the available document.

Do Manh Cuong (2008) redescribed S. guizhouensis, but cautiously states that of course his specimen should be checked against the type. Nevertheless, it is based on this work that I have identified all specimens until now as S. guizhouensis, although there is some variation in color pattern, both as a result of aging and as a result of variability. At least, that is my assumption. Several species may be involved after all.

Nevertheless, the occurrence of two types of females, similar in all outward appearance but the length and shape of the vulvar lamina, was cause for concern. It seemed unlikely that this structural and consistent difference could be explained as intraspecific variability. But no evidently different males could be associated with these long-vulvar females, on the contrary, they occurred together with typical S. guizhouensis males, just like their short vulvar counterparts did in Yen Bai.

The darker specimen of October 4 was in all aspect a normal male, albeit somewhat robust. Total length was 55mm, whereas two specimens I have are 53 and one 55mm. Its bent spoon-like superior appendages are a little more evidently spoon-like in dorsal view than usual. The other specimen was small, 49mm, had a different facial pattern, a small yellow spot between the posterior ocelli, a double yellow band over the occiput, extensive pale yellow on the dorsum of the abdomen, and only a short black streak at the top end of the first lateral suture, normally completely black. The posterior hamule is not as clearly bent at the tip, the superior appendages are not obvisouly spoon-shaped at all, and not as abruptly bent towards the apex. The inferior appendages miss the obvious dorsal tooth near the base, but instead have a more nychogomphus-like shoulder.

Of course it has the typical bifurcate anterior hamule, the anterior branch of which is very long, narrow and hooked at the tip. It also has the typical long posterior lobe to the penile head creating the double jaw wolf head like shape so characteristic of the genus. If Scalmogomphus is a valid genus, its inclusion in the genus appears straightforward.

But all Chinese Scalmogomphus species have the typical basal tooth on the dorsum of the inferior appendages. Their superior appendages are more hooked and spoon-like. In fact they are all so similar in this respect that it is hard to tell them apart. This is why I turned to S. bistrigatus. It is not clear to me whether or not that species always has a clear basal tooth or whether in fact is has more of a shoulder. It appears that the superior appendages are more clearly bent than in the present species, which appears more in between Scalmogomphus and Phaenandrogomphus in this respect. It does have the clear dorsal tooth towards the apex, typical of Scalmogomphus. On the other hand, it has even less black along the lateral suture than expected and the humeral and antehumeral stripes are connected dorsally, something more reminiscent of Phaenandrogomphus dingavani.

Having said that, S. bistrigatus has typically a yellow spot between the posterior ocelli and it has a yellow occiput divided into two by a thin blackish line, exactly as in the specimen. It also has a straighter posterior hamule compared to the other species. And surprisingly, the female has a characteristic that sets it apart from all others in the genus plus P. dingavani. It has extremely long and pointed vulvar lamina, reaching until or past the posterior margin of S10. The confusion in relation to this characteristic was solved by Fraser (1937) and illustrated by Asahina (1988).

The combination of the long-vulvar females and the occurrence of a clearly different male with character traits of Scalmogomphus bistrigatus is quite suggestive. The females have however not been seen in close association with the male. In fact the females of the males of S. guizhouensis have also not been seen in association with those males. They have not been seen at all. Long-vulvar females visit regularly to oviposit. Apparently copulation takes place away from the stream. No short-vulvar females have been observed, even with normal males regularly taking up position on rocks along the stream.

All this offers alternative possibilities: 1) The long-vulvar females in fact are the females of the "typical" males present, which is in that case not S. guizhouensis, but a dark variant of S. bistrigatus, and the a-typical male is a species novum, 2) The long-vulvar females are the females of the a-typical pale male, which in itself may be paler than average, both displaying characteristics of S. bistrigatus, but the male slightly odd, and thus better named S. cf. bistrigatus, or 3) The females are S. bistrigatus, the typical males S. guizhouensis, and the a-typical male is a species novum. For the moment option 2) seems best suited as working hypothesis.

I invite any criticism or suggestions to further help solve this problem.

On the left typical Scalmogomphus guizhouensis, on the right the somewhat smaller, more brightly colored Scalmogomphus cf. bistrigatus. Note also the bright yellow costa.

Top S. cf. bistrigatus, bottom S. guizhouensis. Note the very apparent differences in angulation of superior appendages.

Male Scalmogomphus cf. bistrigatus. Note Phaenandrogomphus/Nychogomphus like appendages and the connected humeral and antehumeral stripes

Male of S. guizhouensis

Long-vulvar female, S. bistrigatus (see also other blog entries on the females)

Facial pattern of S. cf. bistrigatus, with yellow dot between posterior ocelli, yellow occiput and yellow line over postclypeus

Facial pattern of S. guizhouensis, yellow much reduced, black occiput

Appendages on S2, note extremely long and thin anterior hamule anterior branch (extreme right in the picture) and "wolf-jaws" of penile organ (upside down) of S. cf. bistrigatus

The same for S. guizhouensis. Wolf-jaws partly covered in muck, apex of posterior hamule curved

Ventral view of the anal appendages of S. cf. bistrigatus. Note color, small row of denticles on apices and lack of spoon-like appearance

Same for S. guizhouensis. Note the distinct spoon-like shape.

Lateral view of the appendages of S. cf. bistrigatus. Note lack of basal dorsal tooth to inferiors, replaced by shoulder, and gentle curve of superiors. Inferiors and superiors squeezed together as distortion due to heat of microscope's lamp, normally more separated (see scan of lateral view for normal situation). Color a little light due to use of flash, but closer to nature than of photos with microscopic lens below.

Dorsal view of appendages of S. cf. bistrigatus. Inferiors look shorter due to squeeze described above.

Lateral view of appendages of S. guizhouensis, showing clear basal tooth and strong hooked aspect.

Dorsal view of the same. Spoon-like dilation shows in dorsal view as small flap. This is not visible in most specimens.