Heliogomphus bidentatus, Kompier & Karube, 2019

Kompier, Tom & Karube, Haruki, 2019, A new species of Heliogomphus from Vietnam (Odonata: Gomphidae), Zootaxa 4555 (1), pp. 113-120 : 114-119

Heliogomphus bidentatus sp. nov.

( Figs. 1 a–b, d–e, 2a, 3a–c, 4, 5a)

Type specimens. Holotype: ♂, Tam Dao NP, Vinh Phuc Prov., northern Vietnam, 2–8.V.1994, HK leg . Paratypes: 6 ♂♂ 1 ♀, same locality as holotype, 19–24. V.1993, HK leg ; 1 ♂ 3♀♀, same date, location and collector as holotype; 1 ♀, Tam Dao NP, Vinh Phuc Prov., 31. V.1997, Y. Arita leg. ; 1 ♂, Pia Oac NR, Cao Bang Prov. , northern Vietnam, 2. V.1998, K. Matsumoto leg. ; 1 ♂, Yen Bai Prov. , northern Vietnam, 11. V.2014, TK leg .; 1 ♂, Tu Le , near Nam Bung, Yen Bai Prov., 20. V.2014, HK leg .; 1 ♂, Pia Oac NR, Cao Bang Prov. , 9.VII.2014, TK leg .; 1 ♂, Mau Son Mt. , Lang Son Prov., northern Vietnam, 3. V.2015, TK leg .; 2 ♀♀, appr. 21.740 N, 104.277 E, Yen Bai Prov. , northern Vietnam, 16. V.2015, TK leg .; 2 ♂♂, small stream 30km from Cao Bang city, Cao Bang Prov. (566 m alt.), 19. V.2015 Q. T. Phan leg. ; 1 ♀, appr. 16.090 N, 107.464 E, Thua Thien—Hue Prov. , central Vietnam, 19. V.2016, TK leg .; 1 ♀, Pia Oac NR, Cao Bang Prov. , 15.VII.2017, TK leg .; 1 ♀, Xuan Son NP, Phu Tho Prov. , northern Vietnam, 8. VI.2018, TK leg .; 1 ♂, appr. 21.752 N, 104.276 E, Yen Bai Prov. , 10. VI.2018, TK leg .

Additional observations (all by TK): 5 exs., Near Nam Bung, Yen Bai Prov., 10.V.2014; 3 exs. near Nam Bung, Yen Bai Prov. , 11. V.2014; 1 ♂ , Tam Dao NP, Vinh Phuc Prov , 15. VI.2014 ; 1 ex. near Nam Bung, Yen Bai Prov. , 4.VII.2014 ; 2 exs., Pia Oac NR, Cao Bang Prov. , 9.VII.2014 ; 6 exs. Xuan Son NP, Phu Tho Prov. , 18.IV.2015 ; 2 exs., Pia Oac NR, Cao Bang Prov. , 1. V.2015 ; 3 exs., Pu Luong NR, Thanh Hoa Prov. , northern Vietnam, 11. V.2015 ; 2 exs., Yen Bai Prov. , 14. V.2015 ; 2 exs., Yen Bai Prov. , 16. V.2015 ; 5 exs., Xuan Son NP, Phu Tho Prov. , 30. V.2015 ; 1 ex., Pia Oac NR, Cao Bang Prov. , 31. V.2015 ; 1 ex., Thanh Hoa Prov. , 14. VI.2015 ; 6 exs., Pia Oac NR, Cao Bang Prov. , 17. VI.2015 ; 1 ex., Pia Oac NR, Cao Bang Prov. , 18. VI.2015; 1 ♀ , Xuan Son NP, Phu Tho Prov. , 29. VI.2015; 1 ♂ , Ho Chi Minh Highway West, Quang Tri Prov. , central Vietnam, 5. V.2016; 1 ♀ , Ho Chi Minh Highway, Thua Thien—Hue Prov. , 19. V.2016 ; 20 exs., Pia Oac NR, Cao Bang Prov. , 3. VI.2016 ; 3 exs., Tam Dao NP, Vinh Phuc Prov. , 4. VI.2016 ; 1 ex., Ba Vi NP, Ha Noi, northern Vietnam, 6. VI.2018; 1 ♂ , Xuan Son NP, Phu Tho Prov. , 8. VI.2018 ; 1 ex., Xuan Son NP, Phu Tho Prov. , 9. VI.2018 .

Etymology. The species epithet bidentatus refers to the double lateral tooth of the male cerci. A Latin adjective in apposition, meaning double-toothed.

Description of holotype. Head. Labium black, mandibles largely white at base, labrum black, anteclypeus brownish-black, postclypeus black; antefrons black, edge of frons rounded, its dorsal surface covered with broad off-white stripe, its posterior margin centrally invaded with semi-circular black; vertex with ridge connecting lateral ocelli, which extends from each ocellus to occipital ridge and is furnished with sparse, long hairs. Occiput black, posterior part ridged, with a pair of small lateral depressions and a small central rudimentary horn, and with sparse hairs at the posterior margin. Antennae black. Compound eyes mintgreen in life.

Thorax. Prothorax black with pair of yellow oval markings on anterior lobe and small yellow spot in center of posterior lobe. Synthorax black with yellow markings as follows: dorsal stripe, narrowest dorsally and widening towards the collar, where connected to collar stripe to form “7”-shape, the collar stripe interrupted centrally by black of dorsal carina; a humeral spot present; mesinfraepisternum with a very small triangular yellow marking ventrally; mesepimeron with a yellow stripe; metepisternum with a somewhat irregular somewhat darker yellow lateral stripe, which widens somewhat ventrally; metepimeron somewhat darker yellow except for black anterior border. Legs black, femora with numerous small spines; tibiae with two rows of 10–14 long spines.

Wings. Hyaline, slightly smokey. Nodal index: 16–21:20–16 /15–14:15–14; pterostigma dark brown covering 4–5 underlying cells in FW and HW. All supra-, sub-, and triangle uncrossed, apart from triangle of HW, which is two-celled. Anal triangle three-celled, anal loop 1-celled.

Abdomen. Black with yellow markings as follows: S1 yellow except for dorsolateral areas on both sides, which are black but have a small yellowish hump adorned with long hairs; S2 with yellow auricles, yellow band anterior of auricles and a yellow lateral spot near posterior margin and dorsally with a central yellow stripe, somewhat wider anteriorly; S3 with a triangular lateral spot near anterior margin; S4–6 with small yellow lateral spots near anterior margin, progressively smaller from S4 to S6; S7 with a broad dorsolateral yellow band covering anterior one-fourth of segment; a thin longitudinal dorsal stripe running from S3–6; S8–10 black; in dorsal view abdomen widening to about double width from S7 to S10.

Secondary genitalia ( Fig. 4b ). Blackish brown, but anterior hamulus with a pale brown base. Anterior hamule in anterior view about one-third from base slightly widening, its distal half in lateral view with a slightly curved anterior margin and twisted somewhat around its main axis, so that posterior flat surface faces half-laterally nearer the apex. The apex itself strongly hooked, the tip of the hook curved back towards the base of the hamule, in outline reminiscent of a bird of prey’s beak. The proximal half of the anterior hamule in lateral view abruptly constricted along its posterior margin. The posterior hamule in lateral view at base twice the width of the base of the anterior hamule, its lateral surface somewhat concave, its anterior margin s-shaped, its posterior margin smoothly rounded, the apex tapering to a forward directed tooth. Inner surface of both hamuli with long hairs, the posterior hamule also with long hairs on the outside surface close to the tip. Both hamuli in lateral view extending equally far.

Vesica spermalis ( Fig. 4a ). Basal segment large, rounded at anterior end in lateral view, in ventral view widening towards anterior margin and with a median notch; second segment broad in lateral view, gently expanding apically in ventral view; third segment short, with a distinct apical projection; apical segment triangularly projected dorsally, trumpet-shaped, without cornua.

Anal appendages ( Fig. 3 a–c). Black. Cerci in dorsal view ( Fig. 3a ) broad at base, directed obliquely sideways for basal third, with a large triangular lateral expansion and with a slender branch sprouting from the apical third of its interior margin, about twice the length of the broad base and obliquely directed inwards, gently tapering to a blunt point and curving outward again at the apex, the opposite branches almost touching in the middle. In lateral view ( Fig. 3b ) the cerci equally broad at base and somewhat downward slanting, the inner branch visible as slender extension, first dipping ventrally, its apical half slanting upward. The lateral expansion directed ventrally in lateral view, forming a big tooth. A second tooth on the ventral surface of the cercus almost hidden from sight by the first big tooth (see Fig. 2a ), but distinct in ventrolateral view. Epiproct ( Fig. 3c ) widely divaricate, forming two laterally directed points.

Measurements (in mm). HW 42.5; abdomen incl. appendages 46.2.

Variation in male paratypes. Paratypes ( Fig. 1 a–b) very similar to holotype in markings, but second lateral stripe over metepisternum sometimes somewhat narrower and equal in width for complete length. Occipital ridge in several specimens without rudimentary central horn. Wings clear hyaline to smokey, possibly as a result of aging. Anal loop two-celled in one individual, triangle sometimes two-celled in FW, supra-triangle two-celled in both wings in some specimens. Anterior hamule a little shorter than posterior hamule in one specimen. Nodal index with 18–22 Ax and 14–19 Px in FW, 13–16 Ax and 14–18 Px in HW.

Measurements (in mm). HW 39.9–43.5; abdomen incl. appendages 44.0–50.7.

Description of female paratype (16-V-2015, Nam Bung, Yen Bai Prov., TK leg., label marked “specimen used for description”) ( Fig. 1e ). As holotype male, unless specified.

Head ( Fig. 5a ). Labrum with a pair of dorsolateral yellow spots. Occiput with a brown straight raised ridge connecting the compound eyes. Occipital margin with a central horn and long hairs.

Thorax ( Fig. 1e ). Prothorax all black. Synthorax as male, but yellow of same hue everywhere and mesinfraepisternum all black.

Wings. Hyaline with faint amber, somewhat stronger near base ( Fig. 1e ). Nodal index 16–20:20– 14 in FW, 16– 16: 15–16 in HW. Pterostigma brown, covering 6 underlying cells.

Abdomen ( Fig. 1e ). S2 black with a yellow lateral band over auricle, running along whole length of segment, and a broad dorsal yellow line, somewhat narrower posteriorly; S3 with a yellow lateral band running from anterior margin for three-fourth of length of segment; S6 without anterior lateral spot. Vulvar lamina short, triangularly incised.

Anal appendages ( Fig. 1e ). Pointed, black.

Variation in female paratypes ( Fig. 1d ). Horn on occipital margin somewhat variable in size and shape, occasionally divaricate at apex. Occipital area in one female orange brown like occipital ridge. In one female antehumeral spots greatly reduced to almost missing. Triangles is wings varying from uncrossed to two-celled. Pterostigma sometimes with only 5 underlying cells. Amber color of wings variable, probably age-related. 19–22 Ax and 15–18 Px in FW, 14–15 Ax and 14–16 Px in HW. In several females S1 all yellow and lateral stripe on S3 reaching posterior margin. In one female S4 also with lateral yellow band and S5 with broken lateral yellow band, S6 with anterior yellow lateral spot.

Measurements (in mm). HW 40.5–44.1; abdomen including appendages 41.0–46.0.

Diagnosis. The male of Heliogomphus bidentatus can be easily separated in hand by the double lateral tooth of the cerci (compare Figs. 3 a–b with 3d–e). These teeth are similar in size, something not seen in H. scorpio , although that species may possess a subapical step that could be interpreted as a small tooth (see for instance Ris (1912, pg. 72, Fig. 12b)). In addition, the epiproct opens more laterally (compare Figs. 3c and 3f ) and the dorsal view of the cerci differs markedly, with the lateral tooth of H. scorpio curving strongly backwards (compare also Figs. 2a and 2b ). Both male and female of H. bidentatus differ from those of H. scorpio by the hue of yellow on both metepisternum and metepimeron, which is the same yellow as that of the dorsal stripe and first lateral stripe, or slightly darker, whereas in H. scorpio it is clearly paler, a cream-white (compare Figs. 1 a–b and 1d–e with 1c and 1f), a character that is not age-related, but consistent also in older specimens. Otherwise, the patterning is identical. We could not establish consistent differences between the secondary genitalia of the males. The female of H. bidentatus generally has more straight and smooth occipital bar, which is usually grooved and not as straight in the female of H. scorpio (compare Figs. 5a and 5b ), but this character is not fail proof.

Fraser (1942) provided a good overview of all 17 species in the genus known at the time of his publication. There are some inconsistencies in the key he provides in his paper ( H. scorpio , for instance, has dorsal stripes confluent with mesothoracic collar (see Figs. 1c and 1f ), and H. retroflexus has not, contrary to their placement in the key), but his overview of caudal appendages and thoracic markings is very useful. It is immediately obvious that H. bidentatus and H. scorpio are, as far as the shape of the caudal appendages is concerned, similar to H. drescheri Lieftinck, 1929 from Java and H. lyratus Fraser, 1933 from Sri Lanka, although the latter does not have the “7” shaped dorsal markings of the thorax. H. drescheri does. The double-toothed lateral projection of H. bidentatus is unique and helps to separate it from both these species.

Heliogomphus lieftincki Fraser, 1942 is known from a female specimen only, which is distinguished from both H. scorpio and H. bidentatus by a double occipital horn.

The three species not dealt with in Fraser (1942) are H. olivaceus Lieftinck, 1961 , H. borneensis Lieftinck, 1964 , and H. chaoi Karube, 2004 . Heliogomphus olivaceus was described from Palawan in the Philippines. It is a small species, the caudal appendages of which are in dorsal view somewhat similar to H. bidentatus , but in lateral view very different. Its coloration is also very different ( Lieftinck 1961). Heliogomphus borneensis is similar to H. kelantanensis in having very simple cerci for the genus ( Lieftinck 1964) and may well be its junior synonym ( Dow & Stokvis 2018). It bears no resemblance to either H. scorpio or H. bidentatus . Heliogomphus chaoi is another small species, with very different, bi-colored, cerci and the dorsal stripes not confluent with the mesothoracic collar.

Heliogomphus bidentatus is similar in size to H. scorpio , making it one of the larger species in the genus. Like H. scorpio , and unlike most species in the genus, its caudal appendages are all black. In most species in the genus, they are apically or largely white.

Note on ecology. Heliogomphus bidentatus is a species of mountainous areas, where it occurs on small streams under forest cover or in semi-open areas. Males and females perch low on vegetation or on logs and are relatively easy to approach. In northern Vietnam, it flies from mid-April to mid-July (observations from April 18 to July 15). It is not uncommon, but never abundant. Heliogomphus scorpio occurs in a similar habitat (but see below under distribution) and in Xuan Son NP and Tam Dao NP both species can be found in close proximity, inhabiting the same streams and sometimes perching side by side. Heliogomphus scorpio seems to have a slightly later flying season, with observations by the authors from May 7 until August 9. In Xuan Son NP Heliogomphus retroflexus can also be found, although it inhabits larger streams.

During visits in the 1990’s to Tam Dao NP by the second author, H. bidentatus was very common, as were other Gomphidae , with many easily observed, but with ongoing urbanisation the numbers have dropped dramatically.

Distribution. Heliogomphus bidentatus has been recorded in northern and central Vietnam. It is widespread in the mountains, with records from Lang Son Prov. in the northeast, to Cao Bang Prov. and Yen Bai Prov. in the northwest and occurring southward to as far south as the southern border of Thua Thien—Hue Prov. close to the Laotian border. Yokoi and Souphanthong (2014) illustrated an unknown Heliogomphus species from Laos, but their illustrations do not provide enough clarity to identify their species conclusively as H. bidentatus . It is not known from southern China, but may well turn out to occur there, given the close proximity of records from Lang Son Prov. (Mount Mau Son) to the Chinese border.

Heliogomphus scorpio has apparently a partly overlapping distribution, extending into southern and southeastern China, and southward in Vietnam as far south as Phong Nha—Ke Bang National Park in Quang Tri Prov. Within the area of overlap, it sometimes shares the same habitat as H. bidentatus , although at some wellresearched locations, like the Nam Bung area in Yen Bai Prov. or Pia Oac NR in Cao Bang Prov., it has not been found, whereas H. bidentatus is quite common there. It seems that like their distribution, their habitat preferences only partly overlap.

Figures

FIGURE 1. Habitus of Heliogomphus bidentatus [a–b, d–e] and H. scorpio [c, f]. (a) male, 5-V-2016, Quang Tri Prov.; (b) paratype male, 11-V-2014, Nam Bung, Yen Bai Prov.; (c) male, 17-V-2014, Tam Dao NP, Vinh Phuc Prov.; (d) paratype female, 15-VII-2017, Pia Oac NR, Cao Bang Prov.; (e) paratype female (used for description), 16-V-2015, Nam Bung, Yen Bai Prov.; (f) female, 15-VI-2015, Thai Nguyen Prov..

FIGURE 2. Comparison of male caudal appendages in dorsal view of (a) Heliogomphus bidentatus (11-V-2014, Nam Bung, Yen Bai Prov.) and (b) H. scorpio (17-V-2014, Tam Dao NP, Vinh Phuc Prov.).

FIGURE 3. Comparison of male caudal appendages of holotype Heliogomphus bidentatus [a–c] and H. scorpio from Guangdong Prov., China (collection Karube) [d–f] in dorsal view (a, d), lateral view (b, e) and ventral view of epiproct (c, f).

FIGURE 4. Vesica spermalis (a) and hamuli (b) of holotype Heliogomphus bidentatus in lateral view.

FIGURE 5. Occipital area of (a) female Heliogomphus bidentatus (paratype, 16-V-2015, Nam Bung, Yen Bai Prov.) and (b) female H. scorpio (30-V-2015, Xuan Son NP, Phu Tho Prov.).