Three new species of Exocelina Broun, 1886 from the southern slopes of the New Guinea central range, with introduction of the Exocelina skalei group (Coleoptera, Dytiscidae, Copelatinae)

Abstract Three new species of the genus Exocelina Broun, 1886: E. brazzasp. nov., E. amabilissp. nov. and E. mimikasp. nov. are described from New Guinea. The former two species are placed into the E. ekari group, while the latter is suggested to be a member of a separate lineage, the newly introduced E. skalei group. The only other species of that group is E. skalei Shaverdo & Balke, 2014. The group is phylogenetically sister of the E. ekari group. All species have been collected on the southern slopes of the New Guinea central range, a region that remains mostly unsampled.


introduction
Three new species of the genus Exocelina Broun, 1886 were discovered on the southern slopes of the New Guinea central range. Two of them, E. brazza sp. nov. and E. amabilis sp. nov., belong to the largest Exocelina species group, the E. ekari group. To date, this group contains 56 species (including the two new species) endemic to New Guinea (Balke 1998;Shaverdo et al. 2005Shaverdo et al. , 2012Shaverdo et al. , 2016Shaverdo et al. , 2020Shaverdo and Balke 2019). The third species, E. mimika sp. nov., shares the same combination of characters including reduced setation of the paramere with E. skalei . For these two species, the E. skalei group, which is the sister group of the E. ekari group, is proposed. Exocelina skalei is only known from Kaimana in the Bird's Neck region of New Guinea, which is geographically in principle a westward extension of the central highlands, with Kaimana situated at the south coast.
Including the results of this work, 145 species of Exocelina are now described from New Guinea and 202 species worldwide (Nilsson and Hájek 2020;Shaverdo et al. 2020). As in most of our previous papers on the genus, all species data will be presented on the species-id.net portal automatically created by ZooKeys with the publication of this paper.

Materials and methods
The present work is based on material from the following collections: KSP Koleksi Serangga Papua, at the Biology Department of Universitas Cenderawasih (UNCEN), Waena, Papua, Indonesia; MZB Museum Zoologicum Bogoriense, Cibinong, Indonesia.
Our methods follow those described in detail in our previous articles (Shaverdo et al. 2012. The terminology to denote the orientation of the genitalia follows Miller and Nilsson (2003). All specimen data are quoted as they appear on the labels attached to the specimens. Label text is cited using quotation marks; comments in square brackets are ours. The following abbreviations were used: TL (total body length), TL-H (total body length without head), MW (maximum body width).  Type material. Holotype: male "Indonesia: Papua, Dekai, upper Brazza, 300 m, 2/3.vi.2015, near -4,741084724 139,654211075976, Sumoked (Pap045)" (MZB). Paratypes: 2 males, 10 females with the same label as the holotype, one male and one female additionally with green text labels "6991" and "6990", respectively (KSP, MZB).
Colouration: Dorsally brown, with reddish pronotal sides (Fig. 1). Head reddish in anterior half (in front of eyes) and reddish-brown to brown in posterior half (at eye level and behind); pronotum reddish-brown on disc and with broad reddish sides, sometimes also reddish along anterior and posterior margins; elytron reddish-brown to dark brown, with reddish sutural lines; head appendages yellow to yellowish-red, legs reddish. Teneral specimens paler.
Surface sculpture: Shiny dorsally, with fine punctation and microreticulation. Head with dense punctation (spaces between punctures 1-3 times size of punctures), distinctly finer and sparser anteriorly and posteriorly; diameter of punctures smaller than diameter of cells of microreticulation. Pronotum with distinctly finer and relatively sparser punctation than on head. Elytra with very sparse and fine punctation, almost invisible. Pronotum and elytra with weakly impressed microreticulation; head with stronger microreticulation. Metaventrite and metacoxa distinctly but weakly microreticulate, metacoxal plates with longitudinal strioles and transverse wrinkles. Abdominal ventrites with weak microreticulation, strioles, and fine sparse punctation, coarser and denser on two last abdominal ventrites.
Structures: Pronotum with distinct lateral bead. Base of prosternum and neck of prosternal process with ridge, slightly rounded anteriorly. Blade of prosternal process broadly lanceolate, relatively broad and short, slightly convex medially, with distinct bead and few setae. Abdominal ventrite 6 broadly rounded apically.
Habitat. The specimens were collected from a small creek on an almost flat primary forest floor, about 100 m from the upper Brazza River (Figs 3, 4).
Distribution. Indonesia: Papua Province. This species is known only from the type locality (Fig. 5).
Etymology. The species is named after the Brazza River. The name is a noun in the nominative singular standing in apposition.
Affinities. The species evidently belongs to the E. ekari group due to the discontinuous outline of its median lobe. Within the group, it can be placed close to the shiny species with antennomeres 3 and 4 larger than other antennomeres (including the recently described E. athesphatos Shaverdo et al., 2020 andE. tsinga Shaverdo et al., 2020), to which it is assumed to be closely related. However, E. brazza sp. nov. can be easily distinguished from all of them by its small size, shape of the male antennae, median lobe and paramere.   Description. Body size and form: Beetle small: TL-H 2.65-3.45 mm, TL 3.55-3.85 mm, MW 1.75-1.9 mm (holotype: TL-H 3.25 mm, TL 3.65 mm, MW 1.8 mm), with oblong-oval habitus (Fig. 6).
Colouration: Dorsally piceous (Fig. 6), with dark brown posterior part of head and lateral parts of pronotum, and sometimes with middle part of pronotum and elytral sutural lines; head appendages and legs yellowish-red, metathoracic legs darker distally.
Surface sculpture: Relatively shiny dorsally, with very fine, sparse punctation and distinctly impressed microreticulation. Head with dense punctation (spaces between punctures 1-3 times size of punctures), distinctly finer and sparser anteriorly and posteriorly;  diameter of punctures almost equal to diameter of cells of microreticulation. Pronotum with much sparser and finer punctation than head. Elytra with very sparse and fine punctation, often inconspicuous. Pronotum and elytra with distinctly impressed microreticulation; head with microreticulation stronger. Metaventrite and metacoxae distinctly microreticulate, metacoxal plates with longitudinal strioles and transverse wrinkles. Abdominal ventrites with distinct microreticulation, strioles, and very fine and sparse punctation. Structures: Pronotum with narrow lateral bead. Base of prosternum and neck of prosternal process with distinct ridge, slightly rounded anteriorly. Blade of prosternal process lanceolate, relatively broad, slightly convex, with distinct lateral bead and few setae.
Female: Pro-and mesotarsi not modified. Abdominal ventrite 6 slightly truncate or very slightly concave apically, without medial impression and lateral striae.
Habitat. The specimens were collected from the gravel banks of a primary forest stream. The beetles were mainly hidden in the coarse gravel and were only obtained after some digging.
Distribution. Indonesia: Papua Province. The species is known only from the type locality (Fig. 5).
Etymology. The species name is a Latin adjective and means "loveable". Affinities. The species evidently belongs to the E. ekari group due to the discontinuous outline of its median lobe. It is similar to E. utowaensis Shaverdo, Hendrich & Balke, 2012 in modification of the abdominal ventrite 6, body size, colouration and shape but distinctly differs from it in having a pronotal bead (absent in E. utowaensis) and different shape of the median lobe, paramere, and anterolateral hook-like seta of the male protarsomere 4 (it is also larger in E. utowaensis). The species is also similar to E. athesphatos in modification of the abdominal ventrite 6 and paramere, but distinctly differs from it in smaller size and having simple male antennae.
Colouration: Dorsally piceous (Fig. 8), sometimes with dark brown posterior part of head, lateral sides of pronotum, and dark brown elytral sutural lines; head appendages yellowish brown, legs yellowish brown to reddish-brown. Teneral specimens paler. Surface sculpture: Shiny dorsally, with distinct punctation and weakly impressed microreticulation. Head with relatively dense, unevenly distributed punctation (spaces between punctures 1-4 times size of punctures), distinctly finer and sparser anteriorly and posteriorly; diameter of punctures equal to diameter of cells of microreticulation. Pronotum and elytra with punctation sparser and finer than on head and with distinct but weakly impressed microreticulation; head with stronger microreticulation. Metaventrite and metacoxae distinctly microreticulate, metacoxal plates with longitudinal strioles and transverse wrinkles. Abdominal ventrites with distinct microreticulation, strioles, and fine but distinct punctation.
Structures: Pronotum with distinct lateral bead. Base of prosternum and neck of prosternal process with distinct ridge, very slightly rounded anteriorly. Blade of prosternal process lanceolate, narrow, slightly convex, with distinct lateral bead and few setae. Abdominal ventrite 6 broadly rounded.
Male: Antenna simple. Pro-and mesotarsomeres 1-3 very slightly dilated. Protarsomere 4 simple, narrow, with large, thick, strongly curved anterolateral hook-like seta. Protarsomere 5 ventrally with anterior band of more than 50 and posterior row of 20 relatively long setae (Fig. 9D). Median lobe robust, with continuous outline and without setation; lateral margins thick in apical half; apex with very short blunt prolongation in lateral view and deeply concave in ventral view (Fig. 9A, B). Paramere without dorsal notch and with reduced setation: setae very thin, inconspicuous, sparse, longer subdistally and proximally and very short medially (Fig. 9C). Abdominal ventrite 6 broadly rounded, with 2-7 lateral striae on each side.
Habitat. The specimens were collected from rock pools at the edge of a fast-flowing mountain stream.
Distribution. Indonesia: Papua Province. The species is known only from the type locality (Fig. 5).
Etymology. The species is named after Mimika Regency, where it was collected. The name is a noun in the nominative singular standing in apposition.
Affinities and introduction of the E. skalei group. The other Exocelina species known from the Tsinga area is E. tsinga Shaverdo et al., 2020, which is very similar to the new species in size, body shape, colouration, and surface sculpture. The males of these species can be easily distinguished due to the modified antennae of E. tsinga and different shape and setation of their genitalia; female identification, however, could be problematic.
Based on morphological characters, we cannot place the new species in any known species group. The new species resembles representatives of the E. jaseminae group in the shape of the median lobe and E. mekilensis Shaverdo & Balke, 2019 and species of the E. ullrichi group  in the reduced setation of the paramere. However, in the shape of the median lobe and setation of the paramere, the new species is the most similar to E. skalei. Thus, we assume that these two species might be closely related. Exocelina skalei has been so far treated as a member of the E. ekari group but according to the molecular analyses, it is the sister clade of the E. ekari group (Toussaint et al. 2014(Toussaint et al. , 2015. Therefore, for E. skalei and E. mimika sp. nov., herein we introduce a new species group, the E. skalei group, with the following diagnostic characters: -beetle small or medium-sized (TL-H 2.9-5.0 mm), with continuous body outline of broadly oval or oblong-oval shape; -elytra without striae/strioles, with distinct punctation, beetles shiny or submatt; -pronotum with distinct lateral bead; -antennomeres not modified; -male protarsomere 4 simple, with medium-sized or large, slightly or strongly curved anterolateral hook-like seta; -median lobe of aedeagus without setation, with continuous or slightly discontinuous apically outline; -paramere without dorsal notch and with strongly reduced setation: setae very thin and sparse, some longer setae distinct subdistally; setae tiny, inconspicuous medially and proximally.
Since the southern slopes of the central range is a poorly studied area, we assume that more species of the E. skalei group await discovery. The new material, including its molecular analysis, would help to confirm group delimitation.