Oosternum

Hebauer, Martin Fiká Č Ek Franz & Hansen, Michael, 2009, Taxonomic revision of New World species of the genus Oosternum Sharp (Coleoptera: Hydrophilidae: Sphaeridiinae) I. Definition of species groups and revision of the Oosternum aequinoctiale group, Zootaxa 2054, pp. 1-37 : 10

Key to Oosternum species groups

1. Pronotum bearing weak (see Fig. 13 in Smetana 1978) to very high longitudinal costae ( Figs. 11–12 ). Frons between eyes elevated above remaining surface ( Fig. 27 ). Prosternal plate with large lateral cavities ( Fig. 23 ). Elevated por- tion of metaventrite nearly reaching lateral margins of metaventrite, not pentagonal ( Fig. 29 )...... O. sculptum group

- Pronotum evenly convex, without any trace of longitudinal costae. Interocular portion of frons not elevated ( Fig. 28 ). Prosternal plate without deep lateral cavities ( Figs. 24–26 ). Elevated portion of metaventrite pentagonal, con- fined to median portion of the metaventrite ( Figs. 30–31 ) .......................................................................................... 2

2. Elytral series 10 short but present, situated anteriorly between series 9 and elytral margin ( Fig. 17 ) ........................... ....................................................................................................................................................... O. soricoides group

- Elytral series 10 absent ( Fig. 18 ) .................................................................................................................................. 3

3. Pronotum more convex than elytra ( Figs. 15–16 ) ....................................................................................................... 4

- Pronotum not more convex than elytra ( Figs. 13–14 ). ................................................................................................. 6

4. Median portion of prosternum at most slightly elevated, weakly demarcated from lateral portions ( Fig. 24 ). Elytral interval 2 as wide as interval 3 ( Fig. 22 )..................................................................................................... O. group A

- Median portion of prosternum demarcated from lateral portions by sharp ridges ( Figs. 25–26 ). Elytral interval 2 much narrower than interval 3 ...................................................................................................................................... 5

5. Prosternal plate narrow, 1.0–1.5× wider than long ( Figs. 26 , 66–71). Median lobe of aedeagus with lateral projec- tions (Figs. 36–41) .................................................................................................................... O. aequinoctiale group

- Prosternal plate very wide, ca. 2.0× wider than long (as in Fig. 25 ). Median lobe of aedeagus without lateral projec- tions ............................................................................................................................................................ O. group B

6. Median portion of prosternum demarcated from lateral parts by sharp ridges ( Figs. 25–26 ) ...................................... 7

- Median part of prosternum at most slightly elevated, not demarcated from lateral portions by sharp ridges (as in Fig. 24 ) ................................................................................................................................................................................. 9

7. Elytral interval 2 slightly narrower than interval 3, quickly narrowing posteriad and not reaching elytral apex ( Fig. 21 ) .................................................................................................................................................... O. sahlbergi group

- Elytral interval much narrower than interval 3, continually narrowing posteriad, reaching elytral apex ( Figs. 19–20 ). ...................................................................................................................................................................................... 8

8. Prosternal plate ca. as long as wide (as in Fig. 26 )............................................................................... O. sharpi group

- Prosternal plate very wide, ca. 2.0× wider than long ( Fig. 25 )....................................................... O. attacomis group

9. Elytral interval 2 much narrower than interval 3 (as in Fig. 20 ) ................................................... O. pubescens group

- Elytral interval 2 ca. as wide as interval 3 (as in Fig. 22 )............................................................................. O. group C

Figures

FIGURES 11 – 26. Characters for distinguishing species groups of the genus Oosternum (see Table 1 for details). 11 – 12, 23: O. sculptum group; 13 – 14: O. group C; 15 – 16, 19, 26: O. aequinoctiale group; 17: O. soricoides group; 18, 21: O. sahlbergi group; 20, 25: O. attacomis group; 22, 24: O. group A.

FIGURES 27 – 31. Characters for distinguishing species groups of the genus Oosternum (see Table 1 for details). 27, 29: O. sculptum group; 28: O. attacomis group; 30: O. aequinoctiale group; 31: O. sharpi group.