Bidessus, Sharp, 1882

Bergsten, Johannes, Ranarilalatiana, Tolotra & Biström, Olof, 2020, A new species of Bidessus from Anjozorobe-Angavo and a review of Malagasy Bidessus (Coleoptera, Dytiscidae), European Journal of Taxonomy 720, pp. 1-18 : 3

Key to species of Bidessus on Madagascar

1. Elytral stria long, approximately half the length of elytron ( Figs 1A , 2C ) ...................................... 2

– Elytral stria short, distinctly shorter than half the length of elytron ( Figs 1 B–D, 2A–B) ................ 3

2. Elytral stria straight ( Fig. 1A ); female ventrite with a deep, longitudinal furrow; female elytron posteriorly with a distinct, lateral extension ( Fig. 1A ) ...... B. apicidens Biström & Sanfilippo, 1986

– Elytral stria sinuate ( Fig. 2C ); female ventrite simple, no longitudinal furrow; female elytron posteriorly smooth, lacks extension .................................................. B. longistriga Régimbart, 1895

3. Small species (max. length 1.5 mm); elytra with distinct, longitudinal, pale markings ( Fig. 2B ) ..... .................................................................................................................. B. perexiguus Kolbe, 1883

– Larger species (length 1.5–2.0 mm); elytra predominantly dark, sometimes with minor, vague, pale markings ( Figs 1 B–D, 2A) ............................................................................................................... 4

4. Frontal transverse depression of head transformed to four minor, slightly vague, tubercles ( Fig. 1B ) ................................................................................................. B. cf. ceratus Guignot, 1941

– Frontal transverse depression of head not transformed to small tubercles (depression laterally distinct, medially vague) ................................................................................................................... 5

5. Head and pronotum mainly pale, testaceous ( Fig. 1D ) ................... B. cf. nero Gschwendtner, 1933

– Head distinctly darker than pronotum ( Figs 1C , 2A ) ....................................................................... 6

6. Elytral stria longer (approximately ⅓ of elytron length); body shape broad ( Fig. 1C ); pronotum extensively pale (dark markings reduced to narrow areas close to frontal and posterior edges) ( Fig. 1C ); antenna pale ( Fig. 1C ) .................................................................... B. anjozorobe sp. nov.

– Elytral stria short (less than ⅓ of elytron length); body shape slender ( Fig. 2A ); pronotum extensively dark (pale markings reduced to quite narrow medial area, often divided into two separate spots) ( Fig. 2A ); antenna segments 4–11 dark ( Fig. 2A ) ................................. B. nesioticus Guignot, 1956

Figures

Fig. 1. Habitus photographs of Malagasy species of Bidessus Sharp, 1882. A. B. apicidens Bistr̂m & Sanfilippo, 1986, ♀, paratype, http://id.luomus.fi/GL.8408 (FMNH). B. B. cf. ceratus Guignot, 1941, http://id.luomus.fi/GC.2001 (FMNH). C. B. anjozorobe sp. nov., paratype (NHRS-JLKB000025034). D. B. cf. nero Gschwendtner, 1933 (NHRS-JLKB000025032).

Fig. 2. Habitus photographs of Malagasy species of Bidessus Sharp, 1882. A. B. nesioticus Guignot, 1956 (NHRS-JLKB000025031). B. B. perexiguus Kolbe, 1883 (NHRS-JLKB000025029). C. B. longistriga Régimbart, 1895 (NHRS-JLKB000025028).