Macrogomphus phalantus jayavarman, Kosterin, 2019

Kosterin, Oleg E., 2019, New synonyms and a new subspecies of Macrogomphus Selys, 1858 (Odonata: Gomphidae) from continental south-east Asia, Zootaxa 4615 (1), pp. 57-90 : 79-88

Macrogomphus phalantus jayavarman , subspecies nova

Figs. 12–14 , 15 a–f, 16

Holotype: ♂ ( Fig. 12a , 15 a–f), Cambodia, Siem Reap Province, 1.5 km SSW of Kampong Pluk village, 70 m S from northern bank of Lake Tonlé Sap , low, open temporarily flooded forest, 13.1955–1962° N, 103.9720–9730° E, 4 m a.s.l., 15 vi 2018, O. Kosterin leg. Deposited in RMNH . Paratypes: 5 m ♂ # ( Fig. 13 ), 1 ♀ ( Fig. 12b , 16 ), the same data; in RMNH and the author’s collection .

Etymology. The subspecies name, a proper noun in nominative case in the function of apposition, is given after Jayavarman II, the founder of the famous Angkor Empire and its first ‘Divine King’, who in early IX century established its first capitol Hariharalaya (presently Roluos, Prasat Bakong District) situating just 14.5 km N of the type locality of the new subspecies.

Holotype male. Body brownish-black with light-yellow and brownish-yellow markings ( Fig. 12a , see also a paratype in Fig. 13 ).

Head. Eyes green in life ( Figs. 13–14 ). Labium brownish. Face ( Fig. 15a ): Mandible bases light-yellow. Labrum brownish-black with a pair of large rounded-subtriangular yellow spots. Anteclypeus dark-reddish-brown. Postclypeus mostly brownish-black gradually changing to reddish-brown at sides, with a pair of narrow yellow spots at anterior margin. Frons vertical surface changes from reddish-brown at anterior margin to brownish black at rib, horizontal surface with a broad light-yellow transversal stripe. Vertex reddish-brown to brownish-black, with indistinct brownish-yellow spots laterad of lateral ocelli and a pair of very obscure brownish spots on horizontal surface. 1 st antennal segment reddish-brown with yellowish apex; rest of antenna dark-brown. Top of head black. Occipital plate even and simple; with two very slight vertical folds going from eye corners to hind margin and, on frontal surface between them, with an oval shape formed by very slight linear depressions. Hind margin of occipital plate coarse, fringed with long hairs, arched in dorsal view, very slightly raised near eyes in frontal view.

Thorax brownish black with light-yellow pattern ( Figs. 12a , see also a paratype in Fig. 13 a–b). Anterior lobe of prothorax black with a broad yellow margin, median lobe brownish-yellow at sides, dorsally black with a pair of twin adjacent yellow spots in centre; propleuron brownish with an indistinct yellow anterioventral spot, posterior lobe black with a yellow central spot.

Collar stripes of synthorax fused to antehumeral stripes not reaching posterior mesepisternum margin, broadening anteriorly and forming thick 7-like shapes. There is a pair of tiny, short antealar streaks next to prominence of antealar ridge. Anterior triangle and interalar sclerites conspicuous light-yellow. Lateral light-yellow stripes on mesepimeron and metepimeron broad and even. Mesothoracic stripe twice as short as those, narrower, darker brownish-yellow and with indistinct margins. Ventral half of mesinfraepisternum and posterioventral part of metinfraepisternum yellow. Ventral side of synthorax blackish-brown with an indistinct brownish streaks at middle and along lengthwise sutures.

Anterior parts of pro- and mesocoxae and outer surface of metacoxa yellow, rest of coxae brownish; trochanters brownish; legs brownish-black.

Wings ( Fig. 12a ; see also a paratype in Fig. 13a ) hyaline, venation blackish brown but antenodals and postnodals somewhat paler yellowish-brown. Bases with diffuse patches of quite a strong brown enfumation which gradually extends to 1 st antenodal in costal field, to 2 nd antenodal in subcostal field and to 2 nd cubito-anal vein in cubito-anal field, while medial and field and anal area without enfumation. Arculus situated shortly behind 2 nd antenodal but exactly at it in right HW. Antenodals 19 (1 st and 7 th primary) in FW, 12 (left)–13 (right) (1 st and 6 th primary) in HW, postnodals 10 (right)–11 (left) in FW, 11 (left)–13 (right) in HW. Two cubito-anal veins in all wings. Triangles not crossed. Crossveins between Arc and R 1– R 4 bifurcation: 5 (right)–6 (left) above RS, 4 (right)–5 (left) below RS in FW, 4 (left)–5 (right) above RS and 3 below RS in HW. Anal loop one-celled. Anal triangle 3-celled, its outline nearly equilateral triangular but proximal cell larger than ventral cell and central cell more high than long. Tornus rounded. Membranule extremely narrow, almost absent, brownish. Pterostigmata dark brown with black bordering veins, of which dorsal one curving and swollen, ventral one nearly straight and only slightly swollen, below covering 5.5 cells in FW and 6 (left)–7(right) cells in HW.

Abdomen brownish black with light-yellow and brownish-yellow markings ( Fig. 12a , see also a paratype in Fig. 13 ). S1 with a broad dorsal light-yellow spot with uneven margins; posterioventral part of tergite brownish-yellow, rest of tergite sides blackish. S2 with a dorsal light-yellow spot with a broader proximal part broadening to transversal suture where the spot abruptly narrows to a narrower distal part broadening again to posterior segment margin; auricles light-yellow above; sides of S2 brownish-black with large light-yellow anterioventral and posterioventral spots; anterioventral tergite corners brown; secondary genitalia brownish-black. Pattern of S3–S6 corresponds to the dashed male morph of M. parallelogramma . S3 with a pair of large subtriangular anteriolateral brownish-yellow spots occupying ca 1/3 of segment length and well isolated from a light-yellow middorsal streak throughout segment length. S4–S6 with pairs of quadrangular brownish-yellow anteriolateral spots occupying ca 1/5 of segment length, ventrally accompanied with indistinct brownish lightenings of ground colour; S4 with a light-yellow middorsal streak throughout segment length; S5–S6 with short streaks of the same length as anteriolateral spots. Proximal half of S7 occupied by brownish-yellow area, with semicircular incision of black at anterior margin. S8 black with a pair of subtriangular anteriolateral yellow spots. S9 black with a pair of lateral brownish-yellow streaks extending for anterior 2/5 of segment length. S10 black with a pair of indistinct anteriolateral brownish-yellow spots ( Fig. 15d ).

Cerci ( Fig. 15 d–f) as in the nominotypical subspecies ( Fig. 15h ; Lieftinck 1935: fig 12), as discussed above: in dorsal view, proximal inner swelling sharp and shifted distally from level of cleft.

Accessory genitalia ( Fig. 15 b–c) as in the nominotypical subspecies ( Fig. 14g ; Lieftinck 1935: fig 11).

Measurements (mm): HW 37.5, Ab 46; total length 63.5; Pt 4.5.

Variation in male paratypes. The male paratypes are nearly identical to the holotype. In four of them the pale colour is more expressed in the face: the sides of the postclypeus have large brownish-yellow areas with indistinct borders and the two brownish-yellow spots on the vertex vertical surface more expressed. Measurements vary as follows: HW 37–37.5, Ab 45–48.5. FW antenodals: 16 (1 case), 17 (1 case), 18 (3 cases) or 19 (5 cases); FW postnodals: 10 (4 cases), 11 (5 cases) or 12 (1 case); HW antenodals: 11 (2 cases), 12 (1 case), 13 (5 cases) or 14 (2 cases); HW postnodals: 10 (2 cases), 11 (6 cases) or 12 (2 cases).

Female ( Fig. 12b ; 16 ). A somewhat teneral specimen. Similar to male but with a more brownish ground colour and a more extended yellow pattern ( Fig. 12b ), differing in the following traits.

Head ( Fig. 16a ): Postclypeus with large lateral yellow spots adjacent to narrow spots at anterior margin. Indistinct yellow spots laterad and below lateral ocelli. An indistinct brownish-yellow transversal stripe across vertex, nearly interrupted at middle. Occipital ridge simple and even, coarse, its margin gently bent behind and slightly raised at eyes.

Thorax ( Fig. 12b ): no anterior triangle.

Wings as in male but basal brown enfumation stronger and involves all fields, extends to 3th antenodal in costal field, 5 th antenodal in subcostal field, to arculus, occupies cubitanal area entirely, penetrates into supertrigones, present in first 3 cells of anal area. Antenodals 17 (left)–18 (right) (1 st and 6 th primary) on FW, 12 on both HW (1 st and 5 th (left)– 6 th (right) primary); postnodals 11 (left)–12 (right) on FW, 11 on HW.

Abdomen ( Fig. 12b ) Brownish-black with a brownish-yellow markings of a uniform colour. Sides of S1 mostly yellow but dark dorsally. S2 with brownish-yellow middorsal stripe narrowing distally and a contiguous lateral yellow stripes with uneven margins. S3–S6 with brownish-yellow anterior rings occupying ca 1/3 of segment length, with indistinct borders slightly extending beyond transversal suture; they are fused to middorsal streaks of the same colour going throughout segment length, but on S6 this streak is very narrow, vestigial. Anterior half of S7 brownish-yellow. S8 and S9 with pairs of small and indistinct brownish-yellow anteriolateral spots; their ground colour becomes lighter brown at tergite ventral margins. S10 brownish-yellow anteriorly changing to brownish posteriorly. Appendages dirty-yellowish.

Only left half of vulvar scale ( Fig. 16c ) is seen between folded tergite of the teneral specimen; it looks subtriangular with a convex lateral side.

Measurements (mm): HW 39.5; Ab 48, total length 63.5; Pt 5.

Differential diagnosis. The unique structure of the cerci, with the basal inner swelling shifted distally from the level of the cleft ( Fig. 15d, f, h ) (versus at the level of the cleft in M. albardae , see Figs. 2b , e–f, 3a–h, 4c, 7a, c, 9a, 10), and other two smaller swellings (outer and inner) ‘compressed’ distally at the inner cercus branch, allows to identify this series at the species level as M. phalantus . This solution is supported by the occurrence in swampy lowland forest, which is the specific habitat of M. phalantus .

The type series of the new subspecies contains six almost identical males and a female, which exhibit quite a number of differences from the nominotypical subspecies as described by Lieftinck (1935) but it is not easy to judge which of them are diagnostic, since so far the nominotypical subspecies is represented in collections by just three males and two females reliably identified ( Lieftinck 1935; 1954; Dow 2016), so the variation in this subspecies is virtually unknown. I would nominate for the diagnostic characters the size, the absence of any occipital structures in the female and the brown basal rays in the wings of both sexes.

The new subspecies is larger (males: HW 37–37.5, Ab 45–48.5; female HW 39.5, Ab 48) than M. phalantus phalantus (male: HW 33, Ab 40.5; female: HW 35, Ab 43). However, the number of antenodals is about the same (16–19 in FW, 11–14 in HW; versus 17–18 in FW and 11–13 in HW in M. phalantus phalantus ).

The female of the new subspecies has a simple occiput without any sculpture, while the female paratype of the nominotypical subspecies was described as having the “occipital lamina produced behind, forming a distinct median projection, which itself bears two small and closely approximated knob-like tubercles” ( Lieftinck 1935: 202). Since the female occipital structure may differ within gomphid species, e.g. in Euthygomphus yunnanensis (Zhou & Wu, 1992) ( Asahina 1986 (as Merogomphus parvus ); Kosterin 2016) or Burmagomphus asahinai Kosterin, Makbun & Dawwrueng, 2012 ( Kosterin 2014) , for the time being I find this difference insufficient to claim jayavarman a bona species.

All specimens of the new subspecies have diffuse but conspicuous brown rays in the subcostal and cubital spaces at the wing bases ( Figs 12–13 ). The holotype of M. phalanthus phalanthus had clear wing bases while the male paratype and female paratype had yellowish rays ( Lieftinck 1935).

The most conspicuous difference between M. phalantus jayavarman and M. phalantus phalantus is of course the pale pattern of the abdominal S3–S6, which in the former corresponds to the dashed morph of M. parallelogramma and M. albardae (see above), with small isolated anteriolateral spots, while in the latter it corresponds to the ringed morph of those species, with broad anterior pale rings ( Lieftinck 1935). However, since both these morphs co-occur in the related species M. parallelogramma and M. albardae , it is conceivable that males of M. phalantus are also dimorphic, and it requires further investigation whether either morph is confined to a particular region.

In all male specimens of the new subspecies, S9 has a pair of curious, long and narrow yellow stripes ( Fig. 12a , 13–14 ), while M. phalantus phalantus and M. albardae had spots rather than stripes, which in the former was characterised as smaller than on S8 ( Lieftinck 1935). The only female of M. phalantus jayavarman has pairs of small diffuse lateral spots in S8–S10 ( Fig. 12b ), while that of M. phalantus phalantus had S8 and S10 unmarked ( Lieftinck 1935). The mesothoracic pale stripe in M. phalantus jayavarman is a bit longer than depicted for M. phalantus phalantus ( Lieftinck 1935: fig. 10), extending for half of the distance between the alar ridge and spiracle.

It is noteworthy that the secondary male genitalia structure is very similar to that in M. albardae , only with the anterior knob of the posterior hamulus is less and variably expressed. This supports the view that in this group, the secondary genitalia (of a peculiar shape, with anterior and apical knobs and posterior ridges of variable expression, as seen in the anteriolateral view, Fig. 5f ) provide no reliable specific characters. For the time being I find only the outline of the inner cercus branch (in fact of the margin of its lower flattened surface) to be a reliable structural character distinguishing males of at least M. albardae and M. phalantus and may be M. parallelogramma (see above), and have insufficient information to speculate on female diagnostic characters of these species.

Habitat. Tonlé Sap is the largest freshwater lake in Southeast Asia and represents one of the most productive ecosystems in the world. It is situated in the centre of the Cambodian Floodplain formed by the alluvium of the great Mekong River which has filled the former bay of the Gulf of Siam. It is a natural reservoir receiving the excess water volume of Mekong, which from May to September fails to be completely discharged to the sea via the flat Mekong course. During the summer monsoon, this excess water flows via the Tonlé Sap River (which joins the Mekong at Phnom Penh) into Lake Tonlé Sap. When the Mekong level decreases, the current reverses, so the Tonlé Sap River twice a year changes its direction, while Lake Tonlé Sap cyclically changes its length from 160 km, the area of 2,700 km 2 and an average depth of 1 m in late May to a length of 250 km, the area of 15,000 km 2 and an average depth of 6–9 m in late October ( Mekong River Commission 2005). Yet the lake surface is only slightly elevated above the sea level. In these features Tonlé Sap is somewhat analogous to the epicontinental seas of the Mesosoic. Alike the Niles in Egypt, this huge fluctuating water body has always been the source of living resources, through rice farming and fishing, of millions of people populating of the Cambodian Floodplain and was a pre-requisite of arising of the famous Angkorian Civilisation in IX century, whose capitol was the largest urban centre in the world in XI–XIII centuries.

The natural vegetation of Lake Tonlé Sap banks was the temporarily flooded forest composed mostly of Barringtonia acutangula (L.) Gaertn, Dyospiros sp. and Terminalia cambodiana Gagnep. (L. Everaere pers. comm.). This forest is mostly gone from the northern bank because of human overexploitation but remained in certain refugia, e.g. at a popular touristic site Kampong Pluk village, which I managed to examine before and after the Tonlé Sap minimum level, on 24 ii 2017 and 15 vi 2018, when the level respectively comprised ca 20% and 10% of its maximum. There the flooded forest has its maximum height and density at the banks of the lowermost reaches of the ancient, ca 36 km long and a thousand years old, Roluos Canal starting at the Phnom Kulen Plateau in the north and entering Lake Tonlé Sap near Hariharalaya, the first capitol of the Angkorian Empire (which was situating just 14.5 km N of Kampong Pluk village) presently Roluos village with Bakong, Lolei and Preah Ko Temples.

To the west of the canal the forest soon becomes lower and was partly replanted (there are some rows of low trees) and then changes to temporarily flooded shrubbery. Numerous individuals of M. phalantus jayavarman were found at hot midday of 15 vi 2018 (but none on 24 ii 2017), when the lake level had just started to rise (that is in line with the general trend of tropical gomphids to emerge at the beginning of the water level rise). They occurred at first low and sparse trees facing the open bank of the lake ~ 70 m southerly of it, that time already starting to be inundated by still very low water ( Fig. 17 ). (The tree branches for the height of several metres were speckled by dead colonies of small bivalve mollusks which had formed on them when the water was high, see the left upper photo in Fig. 14 ). Some individuals were found deeper in the low and open part of the forest. These dragonflies hung from vertical branches or, mostly, thin lianas ( Fig. 14 ) at the height of 1–2 m, in shade with some light spots, rarely in open sun. They were not too cautious and easy to catch. The only female collected was somewhat teneral. No exuvia were found but these dragonflies most probably emerged immediately from the lake to which this low forest margin faced. Less probably they could breed in the lowermost canal, the mouth of which was separated from this site by ca 145 m of tall and dense forest, but no Macrogomphus were seen at its banks.

Other Odonata were scarce at that site, represented by Brachythemis contaminata (Fabricius, 1793) (quite a few), females of Crocothemis servilia (Drury, 1770) , Rhyothemis phyllis (Sulzer, 1776) and R. variegata (Linnaeus, 1763) (few). At the lake bank there were numerous B. contaminata and single males of Aethriamanta aethra Ris, 1912 and Orthetrum sabina (Drury, 1770) . At the canal bank there were many B. contaminata, Tholymis tillarga (Fabricius, 1798) and few Ictinogomphus decoratus melaenops ( Selys, 1858) , Epophthalmia frontalis Selys, 1871 , O. sabina, Pseudothemis jorina Förster, 1904. No Zygoptera.

It can be supposed that the banks of Lake Tonlé Sap are the largest habitat of the species in the world and the new subspecies is more numerous than the nominotypical one.

Distribution. The new subspecies is presently known only from Lake Tonlé Sap and most probably is its only endemic among Odonata . This locality is separated by a distance of some 1,300 km and the Gulf of Siam from the presumed range of the nominotypical subspecies in Borneo and Sumatra.

It is unclear if M. phalantus occurs in between of these areas. It cannot be excluded that it occurred there in the past but disappeared because of depletion of lowland swamped forests in the economically advanced Malaysia and Thailand. Anyway this species is an update to the list of twelve generally Sondaic species occurring also in Cambodia and/or southern Vietnam ( Kosterin & Kompier 2018).

Figures

FIGURE 2. Details of some male specimens of Macrogomphus albardae kept in RMNH (courtesy of Jan van Tol): a–d—the male syntype (the labels ‘Holotype’ are misleading); e—“W. Borneo, 0 m. / Singkawang / Penanring / L. Coomans de Ruiter / 24. II. 1932”; f—“S. Sumatra / Terbanggi-Hilir / nr. Menggala / Lampang distr. / 18. VIII. 1936 / M. Bartels”; a—general habitus; b, e–f—S10 and anal appendages, dorsal view; c—head and thorax, dorsolateral view; d—labels of the male syntype. Not to scale.

FIGURE 5. A small male of Macrogomphus albardae of the ringed morph, collected by the author on 21 viii 2018 in Cambodia, Preah Vihear Province, Srae Veal village env.: a—habitus in live colours, dorsal view; b—ditto, lateral view (not to scale); canal appendages, dorsal view; d—ditto, lateral view; e—secondary genitalia, lateral view; f—posterior hamulus, anteriolateral view. Scale bars: upper 2 mm; lower 0.5 mm.

FIGURE 12. Holotype, male (a), and paratype, female (b) of Macrogomphus phalantus jayavarman subsp; nov. Cambodia, Siem Reap Province, 1.5 km SSW of Kampong Pluk village, 70 m S from northern bank of Lake Tonlé Sap, low, open temporarily flooded forest, 13.1956° N, 103.9725° E, 3 m a.s.l., 15 vi 2018, O. Kosterin leg.

FIGURE 13. A male paratype of Macrogomphus phalantus jayavarman subsp; nov. in live colours (the same data as in Fig. 9).

FIGURE 14. Males of Macrogomphus phalantus jayavarman subsp; nov. in nature (the same data as in Fig. 9). On the left upper photo a dead colony of bivalve mollusks is seen on the branch, which appeared when the forest was inundated.

FIGURE 15. Details of male specimens of Macrogomphus phalantus: a–f—M. p. jayavarman subsp; nov., the holotype; gh—M. p. phalantus (After Lieftinck 1935: figs.11–12); a—head, frontal view; b–c,g—secondary genitalia, lateral view; d—anal appendages, dorsal view; e—ditto, lateral view; f—ditto, ventral view; h—dorsal and lateral view. Scale bar 1 mm. Asterisk indicates the proximal inner swellings of the cerci.

FIGURE 16. Details of the female paratype of Macrogomphus phalantus jayavarman subsp; nov., the holotype; a—head, frontal view; b—occiput, frontal view; d—right part of vulvar lamina, ventral view. Scale bar 1 mm.

FIGURE 17. Habitat of Macrogomphus phalantus jayavarman subsp; nov., margin of open temporarily flooded forest 1.5 km SSW of Kampong Pluk village, 70 m S from northern bank of Lake Tonlé Sap, at the beginning of water level rise on 15 vi 2018.