Amusurgus (Amusurgus) caerulus Tan 2022, new species

Amusurgus (Amusurgus) caerulus, new species

(Figs 1–4)

Material examined. Holotype: SINGAPORE • ♂; Pasir Ris mangrove boardwalk; on leaves of Bruguiera cylindrica (L.) Bl. In the canopy; 22 November 2021, nighttime; coll. M. K. Tan (ZRC) (Fig. 1).

Paratypes: SINGAPORE • ♂, ♀ (Fig. 2); same locality and information as holotype (all ZRC).

Generic status. Until this new species can be placed in a trigoniid phylogeny, it is tentatively considered under the genus Amusurgus by the following characters: the vertex more convex than flattened; the apical, subapical and third segments of the maxillary palps are of subequal lengths, the apical segment more elongated than stout (rather than very stout in Metiochodes); the male FW venation is more anastomosed than parallel (female FW venation parallel). Other distinguishing characters between Amusurgus and Metiochodes (sensu Chopard, 1969) are less clear-cut in the specimens: eyes, in lateral view, are almost equally lengthened vertically and horizontally.

The species does not appear to belong to the genus Sectus because the lophi at the posterior of pseudepiphallic sclerite are not separated from the sclerite; and the genus Emerasoma because of its body colouration (not green and light coloured) and symmetrical pseudepiphallus.

Subgeneric status. The presence of tympana on TI indicates that this species should be placed under the subgenus Amusurgus, rather than the subgenus Usgmona Furukawa, 1970.

Diagnosis. The new species differs from all known species of Amusurgus by its dark colouration on the dorsum of the head, pronotal dorsal disk and most of lateral lobe, FWs (both dorsal and lateral fields) and by the shape of its male pseudepiphallus.

The species is most similar to the supposing widespread Amusurgus (Amusurgus) fulvus; but differs by the colouration on the head (face, dorsum and lateral), pronotum and FWs, and the male FW without clear false-mirror (Figs 5A–D). It also differs from A. fulvus by the male genitalia: shape of pseudepiphallic lophi, furrow of the ventro-posterior end of pseudepiphallus and shape of pseudepiphallic parameres (Fig. 5E).

The new species differs from all Australian congeners by the posterior apex of pseudepiphallus; and from all Indian subcontinental congeners by the dark colouration. The species differs from Amusurgus (Amusurgus) xanthoneurus (Chopard, 1940) from Borneo by its male FW venation without primitive false mirror, absence of dark rings on TII and TIII and oblique band on FIII, and possibly its live body colouration (Fig. 6). The posterior apex of male pseudepiphallus is similar to that of Amusurgus (Amusurgus) bispinosus He, Li, Fang & Liu, 2010 from southern China; but differs by its longer lophi and without the characteristic two apical spines.

Additional comparisons. The new species appears similar to Metiochodes karnyi (Chopard, 1930) distributed around Southeast Asia by its darker colouration; but differs by its longer apical segment of maxillary palps and smaller inner tympana, by the pronotal disk and lateral lobe not light coloured and by the shape of pseudepiphallus. It also differs from other Southeast Asian Metiochodes (i.e., Metiochodes flavescens Chopard, 1932, Metiochodes fulvus Chopard, 1940, Metiochodes ornatus Chopard, 1969 and Metiochodes platycephalus Chopard, 1940) by its dark colouration.

There are numerous unidentified Amusurgus and Metiochodes species recorded in Singapore (see Tan, 2017), all of which differ from this new species by their body colourations.

Etymology. The species name refers to the dark colouration (with tint of blue) on the head (face, dorsum and lateral), pronotum and FWs; caerulus = dark blue, blue-black, dark in Latin.

Description. Habitus typical of Amusurgus (Fig. 1). Eyes large, protruding (Fig. 3A). Fastigium of vertex about as wide as antennal scapes, with two rows of long and strong setae (Figs 3A, 3B). Vertex more convex than flattened (Fig. 3A). Apical, subapical and third segments of maxillary palps of subequal length; apical segment more elongated than stout, slightly enlarged distally (Fig. 3C). Pronotal disk about 1.5 times wider than long, strongly pubescent, with a few strong setae along margins (Fig. 3A). Pronotal lobe about as long as wide, with straight margins (Fig. 3C). Legs finely pubescent. TI with inner tympanum medium-sized elongated and oval; outer tympanum small and indistinct. TIII with three pairs of long subapical spurs, three short outer apical spurs and two long inner apical spurs.

Male. FW pubescent (Fig. 4A). Dorsal field with veins, including M, R and Sc anastomosed, can be variable between individuals; with a few cross veins forming cells of different size and shape, but no clear false-mirror. FW venation (Fig. 4A): M emerged from R, narrowly spaced apart; R and Sc broadly spaced apart, with a few cross-veins broadly spaced apart. FW lateral field with three straight and parallel veins (Fig. 3C). Hind wing also pubescent, long and surpassing FWs, nearly reaching apices of cerci.

Subgenital plate longer than broad, with apex bilobed; apical margin incised in the middle (Fig. 4B). Cerci simple, tapering and long surpassing hind femora. Male genitalia (Figs 4C, 4D): Pseudepiphallus [= epiphallus] separated into two lateral parts with both surfaces deeply furrowed: dorsal surface narrowly furrowed; ventral surface more deeply and broadly furrowed, with inner margins of furrow sclerotized, parallel, then curved inwards near basal third into narrower furrow. Posterior edges of pseudepiphallic sclerite forming triangular sclerotized lophi (ps lo); lophus with outer margin straight and dorso-inner margin denticulated and slightly curved, with apex acute. Lophus forming a deep indentation with posterior edges of pseudepiphallic sclerite. Dorso-posterior edges of pseudepiphallic sclerite obliquely transverse, forming a small weakly sclerotized triangular lobe with obtuse apex; ventro-posterior edges of pseudepiphallic sclerite (ps lb) more sclerotized and broadly bilobed, surface sparsely granular. Pseudepiphallic parameres with lateral part sclerotized, elongated, slender triangular, not exceeding posterior edges of pseudepiphallic sclerite; with posterior part weakly sclerotized, obliquely transverse, external edge forming triangular lobe with obtuse apex that barely exceeding posterior edges of pseudepiphallic sclerite. Ectophallic fold weakly sclerotized; with a very long weakly sclerotized virga of acute apex. Ectophallic apodeme sclerotized and very long, reaching base of genitalia. Ramus slender, straight and parallel to each other. Endophallic sclerite elongated and slender (more bulbous basally); with lamella of apodemes large, elongated, triangular.

Female. Habitus similar to males (Figs 2, 3D, 3E). FW with veins more parallel, with a few irregularly-spaced cross-veins forming rectangular cells (Fig. 4E). Subgenital plate wider than long, tapering, apex rounded. Ovipositor barely surpassing hind wings, but not cerci; basal third with margins smooth, faintly narrowing; apical third with dorsal and ventral margins faintly denticulated; ventral valves as long as dorsal valves (Fig. 4F).

Colouration (Figs 1, 2). Males and females do not exhibit sexual dimorphism, generally dark coloured dorsally and laterally (except the lower end), ventral of body pale-coloured with tint of green/ blue, legs pale yellow (Figs 1, 2). Head dorsum dark brown with a pale coloured transverse band between middle of eyes (Figs 3A, 3D). Anterior of transverse band with a dark-coloured triangle spot with pale coloured lateral margins (which join at the frontal rostrum) (Figs 3A, 3D). Scapes dark coloured (Figs 3A, 3B, 3D, 3E). Antennae pale brown with dark rings. Face dark coloured between antennal scapes, otherwise pale coloured with a reddish transverse band that curves dorsad at lateral ends (Figs 3B, 3E). Palpi with segments pale yellow, apical segment slightly darker distally (Fig. 3C). Lateral part of head pale coloured, with dark band behind eyes (Fig. 3C). Pronotum with dorsal disk unicolourous dark coloured (including setae) (Figs 3A, 3D). Pronotal lateral lobe dark coloured, except ventro-anterior angle pale coloured (Fig. 3C). FW dorsal field with cells dark coloured and veins (including M, R and Sc) yellow (sometimes with tint of green) (Figs 4A, 4E); lateral field with cells dark coloured, veins sometimes yellow or dark coloured (Fig. 3C). Legs pale coloured, without patterns; distal part of FIII red brown. Thoracic sternites in males blue green (lost during preservation), less prominent in females (Figs 1B, 2B). Abdominal tergites dark coloured, sternites pale coloured to blue green (in males when alive) (Figs 1B, 1C, 3C). Ovipositor pale basally, red brown thereafter.

Measurements. See Table 1.

Natural history. The species is arboreal, and were found among the leaves of the mangrove tree Bruguiera cylindrica at night. So far, it has not been encountered outside mangrove habitat and hence likely to be a mangrove specialist or associate.

When alive, the males, but less so in females, bear bluish colouration on their thoracic and abdominal sternites (Figs 1, 2). This was also observed in another mangrove specialist Svistella chekjawa (see Tan & Robillard, 2012), but not in other Singaporean Trigonidiinae (Tan, 2017). It remains unclear why the males of these mangrove Trigonidiinae exhibit such colouration.