Porrorhynchus, LAPORTE, 1835

GENUS PORRORHYNCHUS LAPORTE, 1835

( FIGS 1 View Figure 1 , 4E View Figure 4 , 5C View Figure 5 , 6C View Figure 6 , 7E View Figure 7 , 8B View Figure 8 , 9D View Figure 9 , 11A View Figure 11 , 13F View Figure 13 )

Type species: Porrorhynchus marginatus Laporte, 1835

Synonyms: Ceylorhynchus Brinck, 1955

Diagnosis: Within the tribe Dineutini Porrorhynchus can be diagnosed by the following combination of characters: (1) Labrum elongate and triangular in form ( Fig. 4E View Figure 4 ), (2) gular suture incomplete, (3) frons without lateral bead ( Fig. 4E View Figure 4 ), (4) antennal flagellum with 6–8 flagellomeres ( Fig. 5C View Figure 5 ), (5) pronotal transverse impressed line absent, (6) scutellar shield invisible with elytra closed, (7) male protrochanter with setose patch ( Fig. 7E View Figure 7 ), (8) male protarsi narrow ( Fig. 9D View Figure 9 ), (9) protibia expanded distolaterally ( Fig. 8B View Figure 8 ), (10) ventral face of profemur with two rows of setae arranged into large clusters, progressively becoming denser apically, (11) mesotarsal claws weakly sexually dimorphic, (12) metaventrite medially triangular in shape ( Fig. 6C View Figure 6 ) and narrow and (13) female RT with vaginal shield ( Fig. 11A View Figure 11 ). Diagnostic characters (7) and (10) appear apomorphic among all Gyrinidae .

Taxonomy: There are now three species within the genus, following removal of the former subgenus Rhomborhynchus .

Distribution: Widely distributed in Southeast Asia west of Wallace’s line, as far northwest as south-eastern Tibet ( Jäch et al., 2012) and east through southern China ( Fig. 14B View Figure 14 ). One species, P. indicans , known from Sri Lanka ( Brinck, 1980).

Discussion: This genus contains the largest known species of whirligig beetle ( P. landaisi ) and species apparently very sensitive to water quality ( Ochs, 1927; Brinck, 1980). Among the Porrorhynchus species, P. indicans is of the most concern in terms of conservation, found to already be uncommonly encountered and limited in distribution in the 1980s due to deforestation of preferred habitat montane forests within Sri Lanka ( Brinck, 1980). This is especially concerning given the unique information P. indicans can potentially provide for future analyses (see Discussion).

KEY TO THE EXTANT GENERA OF THE DINEUTINI

1. Scutellar shield not visible with elytra closed; mesotarsal claws sexually dimorphic (even if weakly so). Female RT with vaginal shield ( Fig. 11C View Figure 11 , vs)....................................... 2 Scutellar shield visible with elytra closed; mesotarsal claws not sexually dimorphic. Female RT without vaginal shield ( Fig. 12 View Figure 12 )................... 3

2. Pronotum without transverse impressed line; ventral face of profemur with two rows of setae arranged in large clusters, becoming denser apically; protrochanter of male with setose patch ( Fig. 7E View Figure 7 ); mesotarsal claws weakly sexually dimorphic.............................. Porrorhynchus Pronotum with transverse impressed line; setae of ventral face of profemur not arranged into large clusters becoming denser apically; protrochanter of male without setose patch, variously modified or not; mesotarsal claws sexually dimorphic, often strongly so......................... Dineutus

3. Elytra with striae in the form of well impressed lines; protarsus (male and female) compressed often with fused segments; male protarsus ventrally without discus ( Fig. 9F View Figure 9 )........ Enhydrus Elytra with striae in the form of punctures or weakly impressed lines, never as well impressed lines; protarsus without compressed or fused segments; male protarsus ventrally with discus ( Fig. 9A–C View Figure 9 )...................................... Macrogyrus