Mortonagrion arthuri Fraser, 1942

Dow, Rory A., 2011, Mortonagrion indraneil spec. nov. from Borneo, and a redescription of M. arthuri Fraser (Odonata: Zygoptera: Coenagrionidae), Zootaxa 3093, pp. 35-46 : 35-40

Mortonagrion arthuri Fraser, 1942

( Figs. 1, 2, 5, 6 , 9 , 11 , 13, 15 , 17, 19, 21, 23 , 30 )

Mortonagrion arthuri Fraser 1942: 97 –98, figs. 1a,b, (original description male, Penang); — Lieftinck (1954: 70, distribution); — Asahina (1965: 226–227, figs. 1–4, brief description of female, illustrations of both sexes, Mergui Islands, Burma); — Kimmins (1966: 179, note on holotype); — van Tol (1992: 40); — Orr (2005: 45, illustration, male only, female considered unknown); — Tang et al. (2010: 71 –72, distribution, photographs both sexes); — Kosterin et al. (2011: 12 –13, Fig. 1 , discussion, photograph male).

Type material. Holotype 3, Peninsular Malaysia, mainland Penang, Butterworth, 24 xi 1935 (A. Wheeler), in BMNH. Four labels on pin: printed circular card, white with red margin, “ Type ”; small off white rectangular card, handwritten “ MALAYA://Butterworth// 24.XI-1935.//A. Wheeler.//B.M. 1949-13.”; Folded piece of paper, handwritten “ Mortonagrion // arthuri 3” and “Zygoptera”; folded brown paper triangle, handwritten “ Mortonagrion arthuri sp. nov. //(Type) 3 F. C.F. 19 ” and “Garden//Butterworth// 24.11.35.//Arthur//4 yrs//old”. F.C.F. refers to F.C. Fraser.

Other material. 2 3, 2 Ƥ, Thailand, Phang Nga province, Similan Island No. 4, 12 xii 2009, leg. N. Vikhrev, in coll. O. Kosterin; 3, Malaysia, Selangor, Klang area, Connaught Bridge, 14 iii 1958, leg. T.C. Maa, RMNH; 3, Ƥ, Malaysia, Pahang, Tioman Island, “stream – site 4”, 27 vi 1988, leg. National University of Singapore Expedition, RMNH; 4 3, Ƥ, Singapore, Pulau Ubin, back of mangrove, 3 ii 2009, leg. W.J. Ngiam & H.B. Tang, in coll. RAD; 8 3, 2 Ƥ, Singapore, Pulau Ubin, pools and ditches at rear of mangrove, above high tide level, 1 vi 2010, leg. RAD, in coll. RAD; 1 Ƥ, Indonesia, Billiton (Belitung), Tandjong Pandan, 17-19 vi 1936, leg. F.J. Kuiper, RMNH.

Description of mature male ( Pulau Ubin, Singapore, SIN 10_COE1): Head: Labium entirely pale. Labrum dark brown and black, mandible bases brownish. Clypeus mostly olive brown. Antenna with scape black, pedicel brownish, flagellum black. Ocelli whitish. Top of head otherwise bronzy black with a pair of large, bilobed, pale bluish-grey postocular markings ( Fig. 1 ).

Thorax: Prothorax mostly black, except centrally on anterior lobe where greenish, obscure pale areas on the lateral extremities of the posterior pronotal lobe, and pale marks on the lower and rear parts of the propleuron. Posterior pronotal lobe with lateral parts short and narrow, abruptly expanded to rear centrally, this part semicircular in dorsal view ( Fig 5 ). Synthorax with mesepisternum bronzy black, with narrow full length linear pale antehumeral stripes, continued onto the outer part of the mesostigmal plates and slightly extended towards the mesopleural suture near the antealar triangle ( Fig. 11 ). Mesepimeron mostly bronzy black. Metepisternum bronzy black, largely occupied by a complicated pale stripe running rearwards and slightly upwards, past the spiracle and above the level of the interpleural suture, to the antealar carina ( Fig 13 ). Metepimeron almost entirely pale. Venter of synthorax pale. Legs: Coxae and trochanters largely brownish cream. Femora brownish with a dark stripe along the extensor surface and a dark area on the flexor surface shortly above the joint. Tibiae pale brown with a black streak on the upper ca one-fourth of the flexor surface. Tarsi mostly pale brown, darker at joints. Wings, with 10 Px in Fw, 8 Px in Hw. Fw quadrilateral with costal side ca two-thirds distal side, slightly longer proximal side and less than half rear side. Hw quadrilateral with costal side ca 1.5 times as long as distal side, ca 2.5 times as long as proximal side and ca two-thirds rear side. Three postquadrilateral cells in each wing except left Fw, where 2 postquadrilateral cells. Pt brown with paler margin, covering slightly less than one underlying cell.

Abdomen: S1 black above, except behind posterior carina, where pale, laterally black with a transverse lateral stripe. S2 black above but a basal lateral marking that extends onto the dorsum and a marking along the margin of the tergite in its apical ca three-fourths. S3–6 largely brown, becoming darker above on successive segments, with a small pale basal mark, becoming fainter on successive segments, extending dorsally but not meeting centrally. Each of S3–S6 black in rear ca one-fourth. S7 mostly black. S8 black with basal ca two-thirds occupied dorsally by an approximately rectangular pale blue mark ( Figs. 15, 17 ), this extending approximately halfway down the sides. S9 and S10 black. S10 with a pair of triangular projections on hind margin dorsally. Cerci shorter than S10, mostly black and dark brown, but with dorsal basal projections that are white interiorly, of complicated structure as shown in Figs 21, 23 . Paraprocts black and dark brown, slightly longer than S10, hollowed interiorly, tapering and curving inwards to tip, which is slightly upturned. Genital ligula as shown in Fig. 30 .

Measurements (mm): Abdomen without anal appendages 22, paraproct ca 0.5, Hw 14.

Description of Female ( Pulau Ubin, Singapore, SIN 10_COE9): similar to the male described, but overall paler. Differences are listed here. Head: Anteclypeus pale, postclypeus brown with a bluish-green border at sides and along rear margin, where narrowly interrupted centrally. Dorsum of head ( Fig. 2 ) bronzy black with obscure paler areas. Postocular markings similar to male, but larger and less well-defined, pale brownish cream in colour; a transverse stripe of the same colour runs behind the ocelli.

Thorax: Prothorax ( Figs. 6 , 9 ) much paler than in male, propleuron mostly pale blue and brownish cream, anterior pronotal lobe mostly pale blue, middle lobe mottled brownish and pale blue, posterior lobe dark except at lateral extremities, where whitish, and centrally. Posterior pronotal lobe larger than in the male, with the lateral parts longer, the central part not so raised, broad, depressed centrally, viewed dorsally shaped like a broad-based halfbrown disc. Synthorax with mesostigmal plates raised up, so resembling a low ridge, their free margin close against the lateral part of the posterior pronotal lobe (as in Fig. 9 showing another female from Pulau Ubin). Rest of synthorax almost identical to the male, except that ground colour of the mesothorax and metepisternum is pale brown and the stripe on the metepisternum is less well defined. Wings with 10 Px in Fw, 8 in Hw. Quadrilateral in both wings varying slightly from the male. Three postquadrilateral cells in all wings. Pt pale brown with lighter border.

Abdomen: Similar to male, pale markings on S1–2 smaller than in male, those on S3–6 somewhat larger, in lateral view the contrast between the pale brown of most of the segment and the darker apical part very strong. S8 dorsally ( Fig. 19 ) with a pale blue marking in the basal half, this divided centrally almost to the segment base. S9– 10 entirely dark brown. Valves of ovipositor mostly dirty cream and brown, just extending beyond S10. Cerci shorter than S10, conical, brown. Paraprocts well-defined, almost triangular in shape.

Measurements (mm): Abdomen without anal appendages or ovipositor 23, Hw 15.

Variation. Aside from small variations in markings within populations, there appear to be marked colour changes with age and a tendency for the markings on head, thorax and S1–2 of the abdomen to be less well defined in the more northern populations. Tang et al. (2010) stated that two male colour forms exist in the Singapore population, one with postocular markings and pale markings on the thorax blue, and the other with these yellow. However, judging from the condition of specimens I have examined, immature individuals have these markings blue, but they change to a yellowish colour with age, and then fade in very mature individuals. The other markings on the head also tend to change colour and fade with increasing age. In one immature male from Pulau Ubin the inner lobe of the postocular markings is absent. The male Connaught Bridge specimen has pale markings less well defined and greyish brown rather than blue or yellow. The male from Pulau Tioman is teneral and has pale blue markings on the thorax. The female from Pulau Tioman has the ground colour of the mesepisternum brown and indistinct pale thoracic markings; the dorsum of the head is pale greyish brown with indistinct darker areas and no distinct postocular markings. The specimens from Thailand have the dorsum of the head coloured like the female from Pulau Tioman, the ground colour of the mesepisternum greyish brown, and very indistinct pale markings on thorax and S1–2. In contrast the female from Belitung has large postocular markings of the same shape as Singapore specimens; the ground colour of the mesepisternum is dark and the pale markings are well defined. Asahina (1965) states that in a female from the Mergui Islands, Burma: “postocular spot unrecognizable”.

Measurements (mm): Males: Abdomen without anal appendages 22–26, Hw 13.5-16, 9–11 Px in Fw, 8–11 Px in Hw. Females: Abdomen without ovipositor or anal appendages 20.5–26, Hw 13–16.5, 9–11 Px in Fw, 8–11 Px in Hw.

Diagnosis. The male is readily distinguished from all other species of Mortonagrion by the form of its cerci; in particular it is distinguished from the most similar species M. varralli Fraser, 1920 , by having the tips of the cerci much more narrow. The female can be distinguished from that of all other species by the broad and deep half-disc shaped posterior pronotal lobe. M. selenion (Ris, 1916) from eastern Asia has a similarly shaped posterior pronotal lobe, but in that species the middle portion is only as broad as the space between the mesostigmal plates, whereas in M. arthuri it is broader than the space between the mesostigmal plates.

Remarks. Asahina (1965) provided a description of females of arthuri from Burma, but this is very brief. Asahina’s Burmese material is slightly larger than the specimens described here; he gives the abdomen length as 26–27 mm (without stating if ovipositor or anal appendages are included) and Hw length as 18 mm. The colouration of the Burmese females is apparently rather uniformly pale brown, without distinctive markings on thorax or abdomen or distinguishable postocular markings.

Kosterin et al. (2011) commented on the apparent preference for coastal and small-island habitats in this species. Of the locations first put on record here, Connaught Bridge is a coastal site; the exact location of Tandjong Pandan on Belitung is not known, but the Malay word tandjung means cape or headland, strongly suggesting a coastal site; all known locations with the possible exception of that on Belitung are either definitely coastal or on relatively small islands. M. arthuri is not unique within the genus in its preference for coastal locations. M. hirosei Asahina, 1972 , known from China and Japan, inhabits coastal sites. M. martini (Ris, 1900) , known from satellite islands of New Guinea, also has a preference for coastal sites (Dirk Gassmann pers. comm.).

Fraser (1942), whilst stating that the anal appendages of male M. arthuri are “quite different from other species”, suggested a resemblance in colouration to the Indian species M. varralli , the genotype of Mortonagrion ; in fact the anal appendages of the two species are rather similar and M. varralli is likely to be the closest ally of M. arthuri .

Distribution. Southern Thailand, Peninsular Malaysia, Singapore, Mergui Islands of Burma and Belitung Island in Indonesia; this distribution suggests that the species should also be looked for in Sumatra.

Figures

FIGURES 1 – 6. Dorsal view of head of: (1) M. arthuri male; (2) M. arthuri female; (3) M. indraneil holotype; (4) M. indraneil female paratype (SAR 05 _ COE 153). Markings of pronotum, dorsal view, of M. arthuri: (5) male; (6) female.

FIGURES 7 – 10. Prothorax and mesostigmal region of female Mortonagrion (scale bar 100 μm unless otherwise noted): (7) M. alcyone mesostigmal plates in dorsal view; (8) M. amoena posterior pronotal lobe and mesostigmal plates, lateral; (9) M. arthuri posterior pronotal lobe and mesostigmal plates (scale bar 200 μm), lateral; (10) M. indraneil paratype (SAR 06 _ COE 353) posterior pronotal lobe and mesostigmal plates, lateral.

FIGURES 11 – 14. Markings of male synthorax: (11) M. arthuri dorsal; (12) M. indraneil holotype dorsal; (13) M. arthuri lateral; (14) M. indraneil lateral.

FIGURES 15 – 20. Markings of terminal abdominal segments: (15) M. arthuri male dorsal; (16) M. indraneil holotype dorsal; (17) M. arthuri male lateral; (18) M. indraneil holotype lateral; (19) M. arthuri female dorsal; (20) M. indraneil female paratype (SAR 05 _ COE 153) dorsal.

FIGURES 21 – 24. Male anal appendages: (21) M. arthuri dorsal; (22) M. indraneil holotype dorsal; (23) M. arthuri lateral; (24) M. indraneil holotype lateral.

FIGURES 25 – 32. Genital ligula of Agriocnemis, Argiocnemis and Mortonagrion species (scale bar 100 μm): (25) Agriocnemis femina; (26) Argiocnemis rubescens rubeola; (27) Argiocnemis species; (28) Mortonagrion aborense; (29) Mortonagrion alcyone; (30) Mortonagrion arthuri; (31) Mortonagrion indraneil paratype (SAR 05 _ COE 152). Mortonagrion female anal appendages (32) Mortonagrion indraneil female paratype (SAR 06 _ COE 353), scale bar 200 μm.