Amphicnemis rigiketit, Dow, 2019

Dow, Rory A., 2019, Amphicnemis rigiketit sp. nov. from Sarawak, with notes on Amphicnemis remiger Laidlaw, 1912 (Odonata: Zygoptera: Coenagrionidae), Zootaxa 4701 (4), pp. 371-382 : 372-376

Amphicnemis rigiketit sp. nov.

( Figs. 1, 3 , 5, 7 , 9, 11 , 13, 15 , 17, 19 , 21 , 23, 25, 27 , 29, 30 , 31 )

Holotype. 1 ♂ (SAR18_COE58), in forest around stream, near road from Kota Samarahan to Siburan , Samarahan Division, Sarawak, Malaysian Borneo, 1.4096N, 110.4046E, ca 13m a.s.l., 21 ii 2018, leg. R. A. Dow, deposited in the Natural History Museum, London.

Paratypes. 6 ♂♂ (SAR18_COE53-57, 59), 5 ♀♀ (SAR18_COE60-64), location and date as holotype, leg. R. A. Dow , 1 ♂, 1 ♀ to be deposited in the Sarawak Museum, Kuching .

Etymology. The species epithet, rigiketit , is a noun in apposition, formed from the names of two highly skilled Iban (the largest indigenous group in Sarawak) collectors, Ketit and Rigi, employed by the Sarawak Museum in the early Twentieth Century. Both collectors took part in the expedition during which the holotype of A. remiger , the closest species to A. rigiketit , was collected. Although the holotype of A. remiger is attributed to J.C. Moulton (likely merely because it was Moulton who sent the specimen to F.F. Laidlaw and it was not customary at the time to explicitly name native collectors) it is entirely possible that it was actually collected by one of these two collectors. In any case the contributions of the Sarawak Museum’s Iban collectors to our knowledge of Sarawak’s natural history are largely undocumented but significant, see Morris (2018), and deserve wider recognition.

Description of holotype. Head ( Figs 1, 3 ). Labium entirely pale. Labrum black, cream in lower ca one third. Mandible bases cream with dark central patch. Genae cream, this extended narrowly beside compound eye to beyond level of antennae bases. Horizontal surface of clypeus shining black, vertical surface pale brown with intrusions of black from above ( Fig. 1 ). Vertical face of frons shining black becoming dark metallic green above, but largely occupied by irregular, complete cream transverse stripe joined to pale colour on genae. Rest of frons, vertex, occiput and underside of head bronzy metallic green. Ocelli whitish. Antenna bases with broad yellowish stripe on anterior face, this just extending to base of scape, scape black, yellowish at top, base of pedicel yellowish, this extended on anterior and posterior faces as stripe running almost to top, remainder brown, flagella missing.

Thorax. Prothorax ( Figs 9, 11 ) with anterior pronotal lobe cream except anterior carina black, middle and posterior pronotal lobes metallic green, propleuron mostly cream. Posterior pronotal lobe short, collar-like centrally but with rear lateral extremities produced as outward directed, finger-like projections. Synthorax ( Fig. 17 ): mesepisternum, most of mesepimeron, upper part of mesokatepisternum and small area of metepisternum adjacent to antealar carina metallic green, with small pale area in upper part mesepimeron immediately adjacent to antealar carina, remainder of synthorax cream. Legs (left anterior leg absent below trochanter) cream except dark brown to black spines, small dark mark lowest part femur and immediately adjacent part flexor surface tibia, black rings between tarsal segments, tips of claws black. Wings: 12 Px in Fw, 11 (left) or 12 (right) in Hw. Arculus slightly distal to Ax2. R 4 arising well distal to subnodus in all wings, IR 3 joined to it by a short stalk. Pterostigma almost trapezoidal with costal side shorter than anal side, dark brownish grey with whitish border, covering ca one underlying cell.

Abdomen. S1 cream with apical transverse dark mark. S2 metallic green above, cream below. S3–6 largely very dark brown above, cream lower laterally. S7 similar but dark markings extending lower laterally in apical ca onethird. S8 bronzy black above, brownish below. S9 almost entirely bronzy black, S10 dark brown and black above, mostly brownish white laterally, pale brown to rear. Anal appendages ( Figs 23, 25, 27 ) white. Cerci in lateral view ( Fig. 25 ) with upper branch narrow at base, directed gently upwards, narrowing further to ca two-thirds length where abruptly expanded and turned down at slightly more than a right angle, from downturn upper margin running straight then slightly out to rounded apex, lower margin curved. Lower branch tapering from base, directed gently down, abruptly expanding along upper margin at apex with black dorsal interior tooth just before apex. In dorsal view ( Fig. 23 ) upper branch of cercus of approximately even width from base to shortly before ca half-length, lacking any well-defined projection although with a slight swelling just before contraction, expanded apical part appearing as a rounded shelf below an outer ridge running to apex. In ventral view ( Fig. 27 ) lower branch tapering from base, slightly expanded at apex, where very weakly bifurcated. Paraprocts short, pale and brown with short finger like projection directed to rear in dorsal part (lateral view).

Measurements (mm). Abdomen without anal appendages 33.5, cercus ca 1, Hw 21.

Female (based on SAR18_COE64). Overall similar to male except in the thorax and as noted below. Head ( Figs 5, 7 ). Only basal ca one-third of labrum black. Dark patches on mandible bases adjacent to base of labrum. Median ocellus yellowish.

Thorax. Prothorax ( Figs 13, 15 ) with posterior pronotal lobe collar-like centrally in dorsal view ( Fig. 13 ), slightly folded upwards laterally then extended downwards to rear as rounded flap, free margin arching upwards back to base ( Fig 15 ). Almost entire prothorax bluish grey with indistinct darker and lighter areas, lateral parts anterior carina of anterior pronotal lobe black, centrally pale. Postepimeral strip slightly expanded just below posterior pronotal lobe (this is difficult to see because it is in the shadow of the lateral parts of the posterior pronotal lobe, indicated with a white line in Fig. 15 ). Synthorax ( Fig. 19 ) dorsum bluish with a greenish cast, remainder bluish, become paler lower laterally, venter pale. Legs with broad black stripe on extensor surface of femur. Wings with arculus only very slightly distal to Ax 2, 14 Px in Fw, 13 Px in Hw.

Abdomen ( Figs 21 ). S9 blackish with poorly defined pale lateral mark. S10 black below, whitish blue above. Cerci whitish, shorter than S10. Ovipositor pale, not extending further than tips of cerci except for mostly dark brown styles.

Measurements (mm). Abdomen without anal appendages or ovipositor 37.5, Hw 23.5.

Variation in paratypes. Males. There is little variation in markings except for small differences in the pattern of parts of the front of the head, none significant. There is some variation in the shape of the pterostigma with the costal side less short relative to the anal side in some, and R 4 is less distal to the subnodus in some. Many of the paratype males are semi-teneral with distorted anal appendages. Females. Two of the female paratypes are immature with the synthorax pale red to below the interpleural suture and most of the prothorax red. The legs are also pale red and lack the black stripe on the extensor surface of the femur, the brown marks on the abdomen are paler and the pale mark on S9 faint. On one of the mature females the posterior femurs are almost white on the flexor surface, in one of the immature females the femurs are white on middle and posterior legs, and on the other immature female the femurs are partially white on the posterior legs only. One of the mature females has the dark stripes on the extensor surface of the femur reduced. Other variation is minor and similar to that in the male paratypes.

Measurements (mm). Males: 12–14 Px in Fw, 11–12 in Hw, Abdomen without anal appendages 33.5–36.5, Hw 20–21. Female: 12–14 Px in Fw, 11–12 in Hw, abdomen without anal appendages or ovipositor 36.5–38.5, Hw 22.5–23.5.

Diagnosis. The male is easily separated from its known, named, congeners in Borneo except A. mariae Lieftinck, 1940 and A. remiger , by the combination of posterior pronotal lobe lacking a long central horn, pterostigma the same colour in both pairs of wings and not bicoloured, except for a narrow pale border, and the upper branch of the cerci lacking any well-developed projections. Males of A. mariae and A. remiger have a better defined subbasal projection on the cerci (visible in dorsal view, see Fig. 24 here and Plate 15, Fig. 1 in Lieftinck (1940)) and lack the abrupt downturn present in the cerci of A. rigiketit ; the upper branch of the cercus in A. mariae forms a smooth arch (Plate 15, Fig. 1 in Lieftinck (1940)). The shape of the apical part of the lower branch of the cercus is different in A. rigiketit and A. remiger (compare Figs 25, 27 with Figs 26, 28 ). The male of A. remiger has the anterior pronotal lobe almost entirely dark coloured but it is mostly pale in A. rigiketit (and A. mariae ). The lateral extremities of the posterior pronotal lobe are produced as finger-like projections in A. rigiketit but these are lacking in A. mariae and A. remiger . The female can be separated from those of most species by the combination of the same pterostigma characteristics as the male and posterior prothoracic lobe lacking a strong central horn and projected to rear laterally. It can be separated from that of A. remiger by the shape of the lateral parts of the posterior prothoracic lobe and the expansion of the postepimeral strip (compare Figs 15 and 16 ). The female of A. mariae is unknown but may be similar. Using unpublished information supplied by myself, Kosterin & Kompier (2018) noted that the female of A. annae Lieftinck, 1940 is apparently polymorphic in the structure of the posterior prothoracic lobe, with a long central horn present in some individuals in a small number of populations but not in most. The form without the central horn is the only one recorded in Sarawak but this hornless form is easily distinguished from the female of A. rigiketit because in dorsal view the central part of the posterior pronotal lobe appears almost rectangular with the lateral extremities projecting more to the rear in the same view.

Remarks. Although none were taken in tandem, the female is associated with the male by reasonable supposition, males of no other species of Amphicnemis were found at the site. The male is clearly closely related to A. remiger and the female is similar to that of A. remiger , further supporting the association of the sexes. It is likely that some characters of colour and pattern, not mentioned in the diagnosis, also consistently serve to distinguish A. remiger from A. rigiketit , for instance the extent of metallic colouration on the synthorax of males of the and the extent of pale colouration on abdominal segment 10 in females. However, the pattern of the anterior parts of the head is sufficiently variable in both species (and many other Amphicnemis ) that it is of no diagnostic value.

All specimens of A. rigiketit were collected either hanging over a steep sided, turbid stream or around pools or trailside, perched on foliage, in the adjacent forest, which becomes flooded at least occasionally during the wettest periods of the year.

Figures

FIGURE 31. Distributions of Amphicnemis rigiketit sp. nov. (red circle) and Amphicnemis remiger (yellow square). Note that the problematic record of A. remiger from “Murud” (see the Remarks under A. remiger) is excluded from the distribution of that species.

FIGURES 1–4. Amphicnemis rigiketit sp. nov., head of holotype male: (1), dorsal-frontal view; (3) dorsal view. Head of male Amphicnemis remiger (SAR11_12_COE332); (2) dorsal-frontal view; (4) dorsal view.

FIGURES 5–8. Amphicnemis rigiketit sp. nov., head of female described: (5), dorsal-frontal view; (7) dorsal view. Head of female Amphicnemis remiger (BRU13_COE103); (6) dorsal-frontal view; (8) dorsal view.

FIGURES 9–12. Amphicnemis rigiketit sp. nov., prothorax of holotype male: (9), dorsal view; (11) lateral view. Prothorax of male Amphicnemis remiger (SAR11_12_COE332); (10) dorsal view; (12) lateral view.

FIGURES 13–16. Amphicnemis rigiketit sp. nov., prothorax of female described: (13), dorsal view; (15) lateral view. Prothorax of female Amphicnemis remiger (BRU13_COE103); (14) dorsal view; (16) lateral view. The expanded part of the postepimeral strip is indicated with a white line in Figs 15 and 16.

FIGURES 17–20. Lateral view of synthorax of Amphicnemis spp. (17) Amphicnemis rigiketit sp. holotype male: (19) Amphicnemis rigiketit sp. nov., female described; (18) male Amphicnemis remiger (SAR11_12_COE332); (20) female Amphicnemis remiger (BRU13_COE103).

FIGURES 21–22. Lateral view of pattern of terminal abdominal segments of female Amphicnemis spp.: (21), Amphicnemis rigiketit sp. nov., female described; (22) Amphicnemis remiger (BRU13_COE103).

FIGURES 23–28. Amphicnemis rigiketit sp. nov., anal appendages of of holotype male: (23), dorsal view; (25) lateral view; (27) ventral view. Anal appendages of male Amphicnemis remiger (SAR11_12_COE332); (24) dorsal view; (26) lateral view; (28) ventral view. All scale bars 5mm.

FIGURES 29–30. Habitus of Amphicnemis rigiketit sp. nov.: (29) holotype male; (30) female paratype.