Borneodessus, Balke & Hendrich & Mazzoldi & Biström, 2002

Balke, M., Hendrich, L., Mazzoldi, P. & Biström, O., 2002, Borneodessus zetteli, new genus and new species, notes on biogeography and a checklist of Dytiscidae from Borneo (Insecta: Coleoptera: Dytiscidae), Journal of Natural History 36 (8), pp. 963-978 : 964-967

Borneodessus gen. nov.

(®gures 1±7)

Type species. Borneodessus zetteli , sp. n., by present designation.

Size. Length of beetles 2.8±3.5 mm, width of body 1.5±1.9 mm.

Position. Attributed to the Bidessini because of the possession of two-segmented parameres. Two- or three-segmented parameres are an apomorphy for the Bidessini (BistroÈm, 1988a). The plesiomorphic state within the Dytiscidae is the possession of unsegmented parameres. Presence of unsegmented parameres in a few genera sometimes assigned to Bidessini is still a matter of debate. It remains unclear if a character reversal`segmented±unsegmented parameres’ occurred, or if these genera simply do not belong to the Bidessini .

Habitus. Comparably large species of Bidessini , body of robust appearance, broadly ovate with slight discontinuity between elytron and pronotum in dorsal view (®gures 1, 2). Body dorso-ventrally arched (®gure 3). Pronotum broadest at posterior corners; rather parallel-sided over basal half; slightly narrowing towards anterior angle over anterior half. Base of elytron of the same width as the base of pronotum; elytron distinctly broadening immediately posteriad of base thus producing the impression of a pronotal±elytral discontinuity.

Colour. Body and appendages chie¯y ferruginous to yellowish. Elytron with darker patches, these however not very well de®ned and hardly contrasting against the background (®gure 1).

Structures. Head without cervical line. Male head with frontal outline angulate, margined and mediofrontally impressed between the eyes (®gure 1); female head not modi®ed. Pronotum with narrow lateral bead; a short, only weakly impressed basolateral stria present; stria curved. Scutellum not visible. Elytron lacking baso-lateral and sutural stria. Epipleuron without deep basal cavity and/or basal carina; broad anteriorly and narrowing towards apex, visible to level of penultimate visible sternum. Pro- and mesotarsomere 1±3 notably dilated in both sexes; fourth pro- and mesotarsomere small but not completely covered by the preceding tarsomere; pro- and mesotarsus thus not pseudotetramerous. Protarsomere 3 of male slightly shorter than in female. Prosternal process broadly triangular, with distinct ridge.

Male genital. Median lobe of aedeagus simple, without conspicuous structures. Parameres two-segmented; apical segment long and narrow; tip twisted to form a hook (®gure 6).

DiOEerential diagnosis. The most likely candidate as a closer relative of B. zetteli are African Clypeodytes (see BistroÈm, 1988b). Both groups are habitually similar and also share similar parameres; the latter being a potential synapomorphy. However, B. zetteli is larger than the known species of Clypeodytes (1.3±2.4 mm, versus 2.8±3.5 mm in Borneodessus ), and in Borneodessus there is no elytral plica, no epipleural carina and no anteriorly beaded head in both sexes as in Clypeodytes . South-East Asian and Australian Clypeodytes we have studied surely belong to other genera and must be revised urgently.

Habitually, Borneodessus zetteli resembles South American Amarodytes ReÂgimbart, 1900 . The placement of Amarodytes within the Bidessini is a matter of debate, however. Amarodytes species possess unsegmented parameres while twosegmented parameres are thought to be an apomorphy for the Bidessini (BistroÈm, 1988a). Borneodessus zetteli is habitually also similar to species of Africodytes BistroÈm. The latter however possess a head with a cervical line, an elytral stria an unmodi®ed male head. In the key provided by BistroÈm (1988a, modi®ed in Pederzani, 1995) the genus Borneodessus runs to Bidessodes ReÂgimbart. Borneodessus diOEers from the latter as follows: body robust, stout (elongate in Bidessodes ), pronotum broadest at posterior corners (broadest anteriad of posterior corners in Bidessodes ), male genitalia simple (strongly modi®ed in Bidessodes ), male head modi®ed as described above (not modi®ed in Bidessodes ).

Habitat. In shallow water among mats of ¯oating roots and in small isolated puddles, at the edges of streams (®gure 8).

Distribution. Borneo (Sabah and East Kalimantan), see ®gure 8.

Identi®cation key

Modi®ed after Pederzani, 1995, but see also BistroÈm, 1988a (for the ®rst steps, only the positive option is quoted here).

1 Head without impressed cervical line............. 2

2 Aquatic. Legs with swimming hairs............. 5

5 Pronotum with baso-lateral striae.............. 6

6 Epipleuron without diagonal carina crossing near base........ 7

7 Elytra not depressed or slightly so, lacking two discal rows of punctures... 8

8 Elytra lacking both discal and sutural stria. Fore and middle tarsi with fourth tarsomere small, but not entirely covered by preceding tarsomere..... 14

14 Latero-basal striae of pronotum connected by a transverse furrow between them.

Parameres one-segmented. Neotropical......... Amarodytes Latero-basal striae of pronotum not connected by a transverse furrow between them. Parameres two-segmented............. 14A

14A Body elongate; median lobe of aedeagus complex, modi®ed; male head simple;

pronotum widest anteriad of posterior corners. Neotropical and Australian Bidessodes

± Body robust, stout; median lobe of aedeagus simple; male head modi®ed, with frontal outline angulate, margined and mediofrontally impressed between the eyes; pronotum widest between posterior corners. Borneo... Borneodessus gen. nov.