Copelatus variistriatus, Hájek & Shaverdo & Hendrich & Balke, 2021

Hajek, Jiri, Shaverdo, Helena, Hendrich, Lars & Balke, Michael, 2021, A review of Copelatus diving beetles from the Solomon Islands, reporting the discovery of six new species (Coleoptera, Dytiscidae, Copelatinae), ZooKeys 1023, pp. 81-118 : 81

Copelatus variistriatus sp. nov. Figures 10-12 , 22 , 24 , 25

Type locality.

Solomon Islands, Guadalcanal , 4.5 km S of Barana Village, Moka River near "Japanese camp", 09°30.3'S, 159°58.9'E .

Type material.

Holotype: ♂, labelled: " Solomon Islands, GUADALCANAL / ca 4.5 km S of Barana vill., forest / nr. " Japanese camp" & Moka river / 09°30.3'S, 159°58.9'E; 275 m / Jiří Hájek leg., 5.-6.xii.2013 [printed] // HOLOTYPE ♂ / COPELATUS / Copelatus variistriatus sp. nov. / Hájek, Hendrich & Balke det. 2018 [red label, printed]" ( NMPC) . Paratypes : 9 ♂♂, 5 ♀♀, same data as holotype ( NHMUK, NMPC) ; 9 ♂♂, 11 ♀♀, labelled: " Solomon Islands, GUADALCANAL / ca. 3.5 km SE of Barana vill. / (drying up stream in shaded gorge) / 09°29.8'S, 159°59.5'E; 190 m / Jiří Hájek leg., 24.xi.-14.xii.2013 [printed]" ( NHMW, NMPC, ZSMG) . All paratypes with the respective printed red label.

Description of male holotype.

Habitus: elongate oblong oval, broadest at mid-length of elytra; body distinctly convex in lateral view. Body outline continuous, without discontinuity between pronotum and elytra. Dorsal surface shiny (Fig. 10 ).

Colouration: Body colour pitchy brown; head, sides of pronotum and appendages paler, ferruginous.

Head: Rather narrow, ca. 0.57 × width of pronotum, trapezoidal. Anterior margin of clypeus indistinctly concave. Antenna with antennomeres long and slender. Reticulation consisting of moderately deeply impressed isodiametric meshes. Punctation double, consisting of coarse setigerous punctures, and very small punctures spread sparsely on surface; row of coarse punctures present around inner margin of eyes, few punctures present at frontal level of eyes, and several punctures anterolaterally to eyes in fronto-clypeal depressions.

Pronotum: Transverse, broadest between posterior angles (width/length ratio = 2.91), lateral margins moderately curved. Sides with lateral beading very thin and indistinct. Reticulation similar to that of head. Punctation similar to that of head; rows of coarse setigerous punctures present along anterior margin, laterally in longitudinal depression close to sides, several punctures present also in basolateral depressions along basal margin. Few longitudinal strioles present in depressions close to posterior angles; disc of pronotum with shallow medial longitudinal scratch.

Elytra: Base of elytra as broad as pronotal base; lateral margins of elytra slightly diverging in basal half, distinctly narrowing in apical half. Eleven discal (but see variability) and a submarginal longitudinal striae present on each elytron: distance between stria 1 and suture twice bigger than distance between other discal striae; striae 1 and 2 absent at base; stria 10 present only as numerous strioles in basal third of elytra; even striae shortened apically. Submarginal stria rather short, present approximately in third fourth of elytral length. Few longitudinal strioles present in interspaces between suture, stria 1, and stria 2. Reticulation similar to that of head and pronotum, meshes somewhat elongated longitudinally. Punctation consisting of coarse setigerous punctures and very fine sparse punctures; coarse punctures present in row along lateral margin of elytra.

Legs: Protibia modified, angled near base, distinctly broadened anteriorly, club shaped. Pro- and mesotarsomeres 1-3 distinctly broadened, with adhesive setae on their ventral side.

Ventral side: Prosternum sinuate anteriorly, obtusely keeled medially. Prosternal process shortly lanceolate, in cross-section convex, apex obtuse; process distinctly bordered laterally; reticulation consisting of shallow, hardly perceptible polygonal meshes. Metaventrite with microsculpture consisting of polygonal meshes; lateral parts of metaventrite ("metasternal wings") tongue-shaped, slender. Metacoxal lines nearly complete, absent only very close to metaventrite. Metacoxal plates covered with long, deep longitudinal strioles; reticulation consisting of extremely elongated, longitudinal polygonal meshes. Metacoxal processes rounded at posterior margin. Abdominal ventrites I-II with longitudinal strioles; ventrites III and IV with oblique strioles laterally. Tuft of setae present antero-medially on ventrites III-V; ventrite VI with setigerous punctures laterally on either side. Abdominal reticulation consisting of elongate polygonal meshes, longitudinal on ventrites I and II, oblique on ventrite III and transverse on ventrites IV-VI. Punctation consisting of fine, sparsely distributed punctures.

Genitalia: Median lobe of aedeagus (Fig. 22 ) sickle-shaped, with evident dorsal and ventral sclerites; dorsal sclerite without surface sculpture and divided into two parts in apical half: left part shorter than right one, both slightly curved, with small crests, notches and truncate apexes (Fig. 22A, B ); ventral sclerite divided into two parts apically: left part more strongly sclerotised, broader, shorter, with broadly pointed apex, right part longer, partly sclerotised (medially membranous), with elongate, thin apex in shape of weak hook (Fig. 22C ).

Lateral lobes (parameres) of narrow triangular form, with broader subdistal part due to curved setigerous dorsal margin; setae numerous, dense, and strong distally, and distinctly less numerous, weaker and sparser basally (Fig. 22D ).

Female. Similar to male in habitus. Protibia simple, not angled basally and only slightly broadened distally; pro- and mesotarsomeres not broadened, without adhesive setae. Dimorphic; striolate form due to dense striolation matt; strioles present on whole surface of pronotum and elytra, thus elytral striation not recognisable: strioles longitudinal, usually very long, only rarely confluent (Fig. 12 ).

Variability.

The specimens of the type series vary in dorsal body colouration: specimens from drying up stream are generally paler (ochreous) than specimens from Moka River. The highest variability is however in elytral striation: in some specimens short strioles present between suture and stria 1, suggesting the present of “true” stria 1, which is vanished in all studied specimens (thus, the first visible stria is actually stria 2); in addition, strioles presenting in basal third between striae 9 and 10 may confluent into distinct stria in some specimens. On the other hand, all even striae have tendency for reduction, they are often fragmented, persisting only as a few longitudinal strioles or missing completely; in the extreme, only four elytral striae (stria 1, 3, 5, 7) are well preserved on disc with striae 9 and 10 preserved as short strioles (Fig. 11 ). The submarginal stria is missing in ca. one third of all specimens. Generally, the striation is more complete in the specimens from Moka River than in specimens from drying up stream. Additional short strioles may occur irregularly between all discal striae in some specimens. Small differences were detected also in the shape of the male median lobe (cf. Figs 22B , 24 , 25 ).

Measurements.

TL: 5.7-6.7 mm (mean value: 6.4 ± 0.2 mm); holotype: 6.6 mm. TL-h: 5.2-6.1 mm (mean value: 5.7 ± 0.2 mm); holotype: 6.0 mm. MW: 2.9-3.4 mm (mean value: 3.2 ± 0.1 mm); holotype: 3.3 mm.

Differential diagnosis.

Due to variable number of elytral striae, it is quite difficult to classify the new species within the traditional Copelatus species group ( Sharp 1882; Guignot 1961; Guéorguiev 1968). We have tentatively included the species into the C. trilobatus species group, as the state of eleven dorsal striae and a submarginal stria is the most frequent condition in C. variistriatus sp. nov., and the other forms resulting from subsequent reduction of striae. However, the double distance between suture and stria 1 suggested possible presence of twelfth stria in the ground plan of the species, currently absent in all specimens studied.

The C. trilobatus species group includes up to now 24 species occurring in tropics of all continents (see under C. bougainvillensis sp. nov.). However, no species is similar to the new species. Copelatus variistriatus sp. nov. is without any doubts closely related to C. laevipennis sp. nov., from which it differs in slightly smaller body length, more oval habitus, presence of elytral striae, and minor differences in the shape of the median lobe (see also under C. laevipennis sp. nov.).

Etymology.

The species name is composed from Latin adjectives varius (- a, - um, = diverse, variegated) and striatus (- a, - um, = with striae), referring to the variable number of elytral striae in the new species.

Distribution.

The species is known so far only from two localities, ca. 1.5 km apart, along north coast of Guadalcanal .

Habitat.

At the type locality, the species was collected in small side rock pools of a small forest river. At the other locality, the specimens were collected in puddles/pools with muddy bottom made by a temporary forest stream (Fig. 28 ). At both places it was collected together with C. baranensis sp. nov.

Figures

Figure 22. Male genitalia of Copelatus variistriatus sp. nov. (holotype) A median lobe in lateral view, right side B median lobe in lateral view, left side C median lobe in ventral view D left paramere in external view. Scale bar: 0.5 mm.

Figures 9 - 12. Habitus of Copelatus 9 C. urceolus sp. nov. (holotype, TL: 5.1 mm) 10 C. variistriatus sp. nov. (holotype; TL: 6.6 mm) 11 C. variistriatus sp. nov. (male paratype with reduced striae; TL: 6.2 mm) 12 C. variistriatus sp. nov. (striolate female paratype; TL: 5.9 mm).

Figures 23 - 25. Variability of Copelatus male genitalia: median lobe in lateral view, left side 23 Copelatus laevipennis sp. nov. (paratype) 24, 25 C. variistriatus sp. nov. (paratypes). Scale bar: 0.5 mm.

Figures 26 - 28. Habitats of Copelatus in Guadalcanal 26 temporary forest stream near Barana village 27 shaded pool on the same stream 28 small temporary puddles in a gorge along the road from Barana to Lungga river.