Batrachomatus nannup (Watts, 1978) Watts, 1978

Hendrich, Lars & Balke, Michael, 2013, Revision of Australian Matini diving beetles based on morphological and molecular data (Coleoptera, Dytiscidae, Matinae), with description of a new species, ZooKeys 293, pp. 41-64 : 48-49

Batrachomatus nannup (Watts, 1978) comb. n.

Allomatus nannup Watts, 1978: 117 (orig. descr.); Watts 1985: 23 (cat.); Lawrence et al. 1987: 351 (cat.); Nilsson 2001: 261 (cat.); Watts 2002: 30, 46 (cat.).

Type locality.

Bridgetown [Blackwood River, 33°58'02"S, 116°07'58"E], Western Australia, Australia.

Type material.

Holotype ♂: "Bridgetown Nov 8 31 W.A." [handwritten label], "Australia Harvard Exp. Darlington" [printed label], "Holotype Allomatus nannup Det. C. Watts 1976" [handwritten and printed label] (ANIC). Paratype ♂: "Bridgetown Nov 8 31 W.A." [handwritten label], "Australia Harvard Exp. Darlington" [printed label], "Paratype Allomatus nannup Det. C. Watts 1976" [handwritten and printed label], "SAMA Database No. 25-006714" [printed label] (SAMA).

Additional material

(178 specimens): Western Australia: 2 exs., "Nannup-Balingup Road, Blackwood River, 28.IX.1965, E.B. Britton leg." (ANIC); 57 exs., "Blackwood River near Nannup, 20.X.1996, C.H.S. Watts" (SAMA); 8 exs., "Blackwood River near Nannup, 20.IX.2000, C.H.S. Watts" (SAMA); 1 ex., "Blackwood River near Bridgetown, 21.IX.2000, C.H.S. Watts" (SAMA); 20 exs., "Nannup, Balingup-Nannup Road, Blackwood River at Revelly Bridge, 79m, 33.55.226S, 115.48.549E, 25.XI.1996, L. Hendrich leg. (Lok. 33)" (CLH, ZSM); 65 exs., "Blackwood River, 8.3 Km NE Nannup, Revelly Bridge, 79m, 6.I.2007, 33.55.226S, 115.48.549E, L. & E. Hendrich leg. (WA 166)", four specimens provided with green printed labels "DNA M.Balke 1712", "DNA M.Balke 1713", "DNA M.Balke 2771", "DNA M.Balke 2772" (BMNH, NMW, ZSM); 25 exs., "Nannup, Balingup-Nannup Road, Revelly Bridge, 79m, 31.XII.1999, 33.55.226S, 115.48.549E, Hendrich leg. (Loc. WA 6/153)" (CLH, ZSM).

Description.

Measurements. TL = 9.1-9.6 mm, TL-H = 8.2-8.6 mm; MW = 4.0-4.3 mm.

Colour. Dorsal surface shiny, black; appendages reddish. Head black with epistome and labrum lighter (Fig. 5).

Structure and sculpture. Body outline narrowly oval, flattened and only slightly convex, pointed apically. Head with strongly impressed reticulation, meshes moderately large and irregular, some scattered small punctures; reticulation and punctures in pronotum rather weak. Elytron with fine reticulation, with transversely elongate small meshes, virtually impunctate apart from serial punctures, being comparatively large and well marked.

Ventral side with metacoxal plate covered by very fine microreticulation, meshes very elongate, inside minutely and sparsely provided with small punctures. Prosternal process flat, broad, broadly carinate in midline, parallel-sided, weakly pointed apically, weakly margined. Metacoxal lines well separated, subparallel in anterior 2/3, moderately diverging posteriad, area between lines with many small punctures.

Male. Pro- and mesotarsi a little dilated, basal 3 tarsomeres with dense short setae beneath suction cups. Aedeagus: median lobe (Fig. 10 a, b); paramere (Fig. 10 c).

Affinities.

Batrachomatus nannup differs from most specimens of Batrachomatus wilsoni and Batrachomatus larsoni sp. n. in the lack of any reddish humeral angles to elytra, the more flattened and narrowly formed body, and in having the reticulation on the elytra weak without punctuation, instead of moderately strong and punctuate. All three species can be easily separated by the shape of their median lobes and their distribution.

Distribution.

An endemic species of the Blackwood River in south-western Australia. All records between Bridgetown and Nannup but probably more widespread in the Blackwood River and its larger tributaries (Fig. 13).

Habitat.

The Blackwood River is the largest river in south-western Australia. The river begins near Quelarup and runs in a south-western direction through the town of Bridgetown then through Nannup until it discharges into the Southern Ocean at Hardy Inlet near the town of Augusta. The river has 41 tributaries and the upper or larger catchment area of the river is in agricultural areas, while the middle catchment area passes through forested areas, and the lower portion of the river passes into mixed forest, agricultural and residential lands (Wikipedia).

At the sampling localities the Blackwood is partly shaded by old River gum trees. In late spring the adults of Batrachomatus nannup can be either found in larger (6-10 m²) and deeper (40-80 cm depth) sandy pools in the floodzone of the river or among floating roots, rotten twigs and logs in shallow water of protected embayments of the slow flowing river (Fig. 16). In summer and in dryer periods the adults were collected only in the deepest parts of the almost standing river, under larger logs, stones and rotten debris (Fig. 17). When disturbed the beetles can be observed swimming around and coming to the surface.