Metasambus circularis, Cheong, 2016

Cheong, Loong-Fah, 2016, Two new species of the genus Brachycoraebus Kerremans and Metasambus Kerremans (Coleoptera: Buprestidae: Coraebini) from Southeast Asia, Raffles Bulletin of Zoology 64, pp. 284-289 : 287-288

Metasambus circularis , sp. nov.

( Figs. 6 , 7 )

Description. Small and rather slender; surface black with slight purplish tinge; head bronzy green, with strong violaceous reflection on occiput, pronotum with violet tinge along lateral margin; pubescence on elytra white, forming three – at base, middle, and apical fourth – transverse bands (each consisting of two ring-shaped spots), design on apical part more distinct; the three bands becoming somewhat zigzaggy towards lateral margin. Length: 3.8 mm, width: 1.3 mm.

Head slightly grooved on occiput, groove becoming indistinct on front, surface imbricate except at groove area, clothed with white hairs, denser on occiput and clypeal margin. Clypeal suture distinct; epistome narrow, width about 2.5 times less than length; antennae reaching to middle of pronotum.

Pronotum 1.6 times wider than long, greatest width of prothorax near middle; sides flattened and regularly arcuate, very slightly sinuate anteriorly and posteriorly; anterior margin slightly bisinuate, median lobe nearly straight; base strongly bisinuate, with large median lobe broadly truncate in front of scutellum; disk convex anteriorly, broadly concave in basal part, with a rather deep depression inside of lateral carina reaching from base to midlength; lateral carina slightly arcuate, reaching from posterior angles to apical fifth; pronotal surface concentrically rugose on disc, here finely punctured, more coarsely and densely so towards lateral margin; hairs on disc sparse, dark, inconspicuous, recumbent, on sides denser, long, white.

Scutellum triangular. Elytra narrower at base than middle of pronotum, with a slight depression along lateral margin behind humerus; sides slightly sinuate at the level of metacoxae, expanded at apical third, then strongly attenuate to tips, which are separately rounded and finely dentate, with denticulation coarser near the sutural and lateral angles; surface obsoletely imbricate, finely punctate, clothed with inconspicuous hairs of the same colour as the surface, with a series of thicker white setae forming at base, middle, and apical fourth three transverse bands.Ventral side imbricate.

Aedeagus ( Fig. 7 ) expanded near the middle and shorter in comparison to Metasambus weyersi ( Kerremans, 1900) .

Variability: There is also some variation in the amount of reflection on the occiput, ranging from feebly cupreous to obviously violet, and in the design of the pattern on the elytra. In the Singapore specimens, the head is slightly wider (head-to-pronotum ratio 0.69–0.70) than that of the Sumatran specimens (0.67–0.68).

Diagnosis. Very similar to Metasambus weyersi ( Figs. 4 , 5 ), but head distinctly broader: head to pronotum ratio is 0.67–0.70, as compared to 0.61–0.63 in M. weyersi ; vertex simply sulcate (“mamelonne”, i.e., forming two breastshaped domes, in M. weyersi ). The pronotum shows varying degree of twin-peakness, and its concentric rugosity varies from obsolete to moderate, but never as strong as in M. weyersi ; the lateral carina on the pronotum is less distinct, running to apical fifth, and close to the lateral margin, whereas in M. weyersi , it runs more or less distinct, from posterior angle to apical fourth, at a distance away from the pronotal margin, together with it forming the shape of a bow. The elytra is always more parallel sided, whereas in M. weyersi , it is more strongly sinuate at the level of metacoxa; the scutellum shape also differs: the central violet part is bigger and more triangular, whereas the scutellum of M. weyersi is more depressed, with a central violet part small and rather circular; the silver pilosity on the elytra can vary a bit, the median band consists of “ring” broken anteriorly but does not form a wide solid band like that of M. weyersi . Aedeagus different from that of M. weyersi in size, overall shape and shape of the apex. Note that the above measurements and characters of Metasambus weyersi are not included in Kerremans’ original description; they are based on my examination of seven syntypes from NHM and two additional specimens from RBH.

Etymology. The specific name is the Latin adjective circularis describing the circular pattern on the elytra of this species.

Type specimens. Holotype male ( ZRC.COL.102), “ Singapore, Rifle Range [forest]”, coll. L.F. Cheong & Y.W. Cheong, 9 July 2011; 6 paratypes (sex not examined): 1 ex. same data as holotype ( ZRC.COL.103); 4 exs.: Sumatra (RBH), without further data; 1 ex. Sumatra Hindrapoera (RBH), without further data.

Remarks. Of the five Sumatran paratypes, four bear these additional labels: “ Coraebus weyersi Kerr, Sumatra , cotype”, followed by “Not Metasambus weyersi Kerr, B Levey det. 1971”. The fifth Sumatran paratype bears the label: “ Metasambus weyersi Kerr. co-type ”. Despite the label “co-type”, these could be instances when specimens are labelled as ‘co-type’ when they are merely topotypic, or compared with type, and they are actually not types at all. The first four paratypes probably did not belong to the type-series of M. weyersi Kerr. , since the labels are somewhat different (labeled as “ Coraebus weyersi Kerr. co-type ”, not “ Weyersi Kerr. Type”, location is “Sumatra”, not “Sumatra Hindrapoera”, etc.). Furthermore, the fifth paratype is labeled as “ Metasambus weyersi ”, not “ Coraebus weyersi ”. Kerremans described the species as Coraebus in 1900, and only three years later erected the genus Metasambus , so the label for the fifth paratype “ Metasambus weyersi ” must have been attached later. Finally, it should be noted that at this point, it remains impossible to tell whether the original syntype series for Metasambus weyersi is a mixed series or not, even if one were to regard the five M. circularis from Sumatra as not true types. This is because, of the fifteen syntypes mentioned by ( Kerremans, 1900), only a total of nine M. weyersi are available for study for this paper.

Discussion. The three previously described species in this genus are quite widely separated: Metasambus hoscheki in Kiautschou, China (Shandong in NE of China), M. tonkinensis in Indochina, and M. weyersi in Sumatra. There seems to be extensive gaps along the entire range of the genus Metasambus . Yet, is it not anomalous that now, with the addition of this newly described species, we have two closely related species within Sumatra? Given the small and cryptic nature of Metasambus species , an obvious conjecture is that we have poor knowledge of the actual distribution of all the Metasambus species. Or it could be a genus with species having a restricted distribution, but there exist in the Oriental region undiscovered species, which collectively would close the seemingly extensive gaps. Yet another reason for the disjunct distribution could be that some original Metasambus species were eliminated elsewhere by other species better pre-adapted to changes in environmental conditions (e.g., climate). The existence of two closely related species in Sumatra could be a result of recent speciation. Or it could be that both Metasambus weyersi and M. circularis have wider distribution ranges that happen to overlap in Sumatra. Similar existence of pairs or groups of closely related species in one area is also found in other Buprestid taxa: for instance, the interesting case of at least four Exagistus species , three of which are closely related, found on Mt. Trus Madi, Sabah ( Holynski, 2011).

Figures

Fig. 6. Dorsal habitus of Metasambus circularis, sp. nov., holotype male.

Fig. 7. Aedeagus of Metasambus circularis, sp. nov.

Fig. 4. Dorsal habitus of Metasambus weyersi (Kerremans, 1900), lectotype, male, Sumatra, NHM (photo by:Harry Taylor: Natural History Museum).

Fig. 5. Aedeagus of Metasambus weyersi (Kerremans, 1900).