The Australasian Copelatinae genus Exocelina Broun, 1886 (= Papuadytes Balke, 1998, see Nilsson and Fery 2006 and Nilsson 2007) is a current taxonomic and molecular phylogenetic research focus (Balke and Bergsten 2003; Balke et al. 2004a, 2004b, 2007; Watts & Humphreys 2009; Wewalka et al. 2010). Here, we continue our study of the highly diverse New Guinea Exocelina fauna, with 63 formally described species (Balke 1998, 1999, 2001; Shaverdo et al. 2005, 2012). These species form a morphologically homogenous, monophyletic group associated with streams and rivers (e.g. Balke et al. 2007). In the present paper, we describe a new species, which is morphologically distinct and ecologically different from all other known New Guinea species. The closest related species to the new one occur in Australia and New Caledonia.

Studied specimens are in the following collections:

CLH collection of Lars Hendrich, Munich, Germany (property of NHMW)

NHMW Naturhistorisches Museum Wien, Vienna, Austria (M.A. Jäch)

MNHN Muséum National d’Histoire Naturelle, Paris, France (T. Deuve, A. Mantilleri)

ZSM Zoologische Staatssammlung München, Munich, Germany (M. Balke)

Specimens of the following Exocelina species were studied for comparative purposes:

Exocelina australiae (Clark, 1863): 1 male, 1 female “Collect. Plason”, “Copelatus nigritulus Shrp. N. H.[?]” [hand written] (NHMW).

Exocelina ferruginea (Sharp, 1882): 1 male, 1 female “Australia / SA: Adelaide Hills, 5 km W Forreston, Mt. Crawford State Forest, Watts Gully, 200m, 22.11.1999, Hendrich & Watts leg. (Loc. 2/140)” (CLH).

Exocelina inexspectata Wewalka, Balke & Hendrich, 2010: holotype (male) “New Caledonia 12286, 20°25'S, 164°13'E, Nehoue campground, 29 Apr 2005, 10m G.B. Monteith, MV light.”, “HOLOTYPUS Exocelina inexpectata sp.n. Wewalka et al. 2008” [red, printed] (MNHN).

Exocelina knoepfchen Shaverdo, Hendrich, Balke, 2012: 1 male “Papua New Guinea: Eastern Highlands, Kainantu, Yoginofi, 1900m, 9.v.1994, 06.21.799S, 145.45.463E, Balke & Sagata (PNG 55)” (ZSM).

Exocelina simplex (Clark, 1863): 2 males, 2 females “South AU, nr. Penola, roadside pools, 37.380928°, 140.837540°, 30–31.10.2001, M. Balke leg.” (NHMW).

Exocelina ullrichi (Balke, 1998): 1 male “Papua New Guinea: Eastern Highlands, Hogu, 1 km E Mt. Barola, 1900m, 9.v.2006, 06.17.556S, 145.45.036E, Balke & Sagata (PNG 56)”(ZSM). 1 female “Papua New Guinea: Aiyura, 1787m, 15.i.2003, 06 21 411S, 145 54.340E, K. Sagata (WB5)” (ZSM).

All specimen data are quoted as they appear on the labels attached to the specimens. Label text is cited using quotation marks. Our red identification labels were attached to the types.

Measurements were taken using a Leica M205C stereomicroscope. The following abbreviations were used: TL (total body length), TL-H (total body length without head), and MW (maximum body width). Drawings were made with the aid of a camera lucida attached to a Leica DM 2500 microscope. For detailed study and illustration, protarsi and genitalia were removed and mounted on glass slides with DMHF (dimethyl hydantoin formaldehyde) as temporary preparations. The drawings were scanned and edited, using the software Adobe Illustrator CS5.1.

The terminology to denote the orientation of the genitalia (“ventral” for median lobe and gonocoxae and “dorsal” and “external” for paramere) follows Miller & Nilsson (2003). Administrative divisions of Indonesia follow information from Wikipedia (2013).

The new species is morphologically similar to the Australian Exocelina ferruginea (Sharp, 1882) and the New Caledonian Exocelina inexspectata Wewalka, Balke & Hendrich, 2010. It shares with them some characters not found in all other known New Guinea Exocelina and listed below.

1) Striolate elytra (Fig. 1); in Exocelina ferruginea and Exocelina inexspectata elytra without strioles on anterior (basal) 2/3 but with distinct punctures, and in posterior (apical) third with transverse strioles. The striolate dorsal surface of the body is also characteristic for other Australian and New Caledonian species. All other New Guinea species have punctation rather than strioles on elytra.

2) Modification of paramere: prolongation of subdistal part on dorsal side (Figs 4A, 4B). This apomorphic character is observed only in these three species.

3) Presence of a strip of sclerotization on right side of ventral sclerite of median lobe (Figs 5A, 5B). This character is also present in Exocelina ferruginea. The holotype of Exocelina inexspectata is teneral so this character is not evident, but is characteristic for several other New Caledonian species, e.g. Exocelina novaecaledoniae (J. Balfour-Browne, 1939), Exocelina ouin Wewalka, Balke & Hendrich, 2010, and Exocelina jeannae Wewalka, Balke & Hendrich, 2010.

4) Striolate surface of proximal part of median lobe (Fig. 6). It is characteristic of Australian species.

5) Similar modification of pro- and mesotarsus (Figs 2, 3):

- Pro- and mesotarsomeres 1–3 distinctly dilated.

- Protarsomere 4 asymmetrical, with expanded anterior angle where there is a large, strongly curved anterolateral hook-like seta.

Exocelina ullrichi (Balke, 1998) is the only other species from New Guinea, which shares these two characters, see Fig. 29 in Balke (1998).

- Protarsomere 5 simple, ventrally with anterior row of numerous and posterior row of very few long setae. This character is also found in Exocelina ferruginea and in Exocelina inexspectata.

- Pro- and mesotarsal claws long.

- Anterior claw longer than posterior, straighter, and slightly broadened.

The above mentioned modifications of pro- and mesotarsus are characteristic of all known Australian species, with some small variations.

- Anterior claw with fine serration ventrally. This character is also observed in Exocelina ferruginea and Exocelina inexspectata.

- Posterior protarsal claw evenly curved, with two fine denticles on ventral margin. This character is also present in Exocelina ferruginea.

6) Female metatarsi without ventral row of natatorial setae. It is characteristic of known Australian species (in Exocelina australiae (Clark, 1863) also for males).

7) Shape and setation of gonocoxae: apices not rounded, slightly pointed, setation much sparser (Fig. 7A). The gonocoxae of Exocelina baliem are evidently different from those of other New Guinea Exocelina species (Fig. 7C and Fig. 17b in Shaverdo et al. 2005) and much more similar to the gonocoxae of Exocelina ferruginea (Fig. 7B).

Exocelina baliem sp. n. is unique among known New Guinea Exocelina species in its habitat requirements. It inhabits ponds, unlike all other known species of Exocelina in New Guinea, which occur in directly stream related stagnant water, such as rockpools, stagnant backflows, marginal puddles and waterholes along stream banks, and at the immediate stream margin. The habitat of Exocelina baliem sp. n. is similar to that of the closely related Exocelina ferruginea.

Balke et al. (2007) showed that New Guinea Exocelina species form a monophyle-tic group, the result of a single colonization from Australia, and that Australian species, including Exocelina ferruginea, form a "basal" paraphyletic series, followed by the other Exocelina species. Thus, being closely related to Exocelina ferruginea, Exocelina baliem sp. n. represents an older colonization from Australia into New Guinea, but without subsequent radiation. This radiation likely occurred more recently, producing the highly diverse clade of morphologically distinct stream species. Also we assume that New Caledonia was colonized three times out of Australia, not twice as suggested by Balke et al. (2007), since the New Caledonian Exocelina inexspectata is closely related to Exocelina baliem sp. n. and Exocelina ferruginea. The species is known only from the holotype collected at light, and it might also be a pond species, whereas all other known New Caledonian species are stream associated.