CYCLOUS DEJEAN, 1833 SENSU

SUBGENUS CYCLOUS DEJEAN, 1833 SENSU NOV.

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

Type species: Dineutus australis ( Fabricius, 1775) .

Synonyms: Callistodineutus Ochs, 1926 syn. nov., Cyclinus Kirby, 1837 syn. nov., Gyrinodineutus Ochs, 1926 , Paracyclous Ochs, 1926 syn. nov., Protodineutus Ochs, 1926 syn. nov., Spinosodineutes Hatch, 1926 syn. nov.

Diagnosis: Within Dineutus , the Cyclous subgenus can be diagnosed by the following characters: (1) Head capsule with a frons to clypeus ratio less than or equal to 1.5, (2) a transverse, rounded labrum, (3) distolateral angle of protibia without spine, (4) ventral face of protrochanter apically with series of stout setae ( Fig. 8C View Figure 8 ), (5) mesotarsal claws strongly sexually dimorphic and (6) spermatheca not tubiform, less elongate and more rounded. Many species are strongly sexually dimorphic in elytral shape. This group exhibits the most strongly sexually dimorphic mesotarsal claws.

Taxonomy: This is the largest subgenus, now with 67 species. The species were treated taxonomically most recently by Mouchamps (1949a) (the Spinosodineutes species), Brinck (1955b) (African species), Brinck (1976) (the Callistodineutus species) and Gustafson & Miller (2015) (the North American species).

Distribution: Widely distributed, found in North America, Africa, Asia and Australia.

Discussion: The numerous subgenera of Dineutus have long been a source of conflict among gyrinid workers ( Hatch, 1926; Ochs, 1926, 1955; Guignot, 1950; Brinck, 1955b). The first division of Dineutus into subgenera was proposed by Hatch (1926), but the majority of subgenera were erected by Ochs (1926) during his precladistic systematic treatment of the species of Dineutus (and Porrorhynchus , see below). The subgenera have nearly all been diagnosed in the past by body form, modification to the elytral apex and/or elytra reticulation. These characters are highly variable among the numerous Dineutus species and typically not unique to any one subgenus, causing much of the disagreement between constituent species.

The only authority to attempt to propose discrete morphological characters for the subgenera was species. The distinct character of the ventral face of the protrochanter with a series of short stout setae apically, in combination with the other diagnostic features, successfully recognizes a large monophyletic group within Dineutus . While D. ritsemae was not included in the phylogenetic study, the taxon was studied for morphology. Dineutus ritsemae has well-developed sexually dimorphic mesotarsal claws and resembles closely members of the former subgenus Callistodineutus having a single profemoral subapicoventral tooth on the anterior face only. Given the former species are nested within the North American members, including this species and synonymizing Paracylous with Cyclous is justified. For this reason, we here synonymous the former subgenera. The oldest available name for this grouping is Cyclous initially proposed by Dejean, 1833 for Dineutus australis , one of the most widespread species of Dineutus ( Ochs, 1949) .

This subgenus is notable for having numerous sexually dimorphic traits. Many species have sexually dimorphic elytral apices, often with one sex having thorn-like productions. This is exhibited in several North American species ( Gustafson & Miller, 2015). This group also exhibits sexually dimorphic modification to the protrochanter, such as the strange waxy region of male Dineutus proximus ( Fig. 7B View Figure 7 ), and most notably the setose brush of D. australis males ( Fig. 7A View Figure 7 ). The male mesotarsal claws are also strongly sexually dimorphic in this group. The North American species exhibit species-specific sexually dimorphic claws, with the claws of D. nigrior being the most extremely dimorphic known ( Gustafson & Miller, 2015). The median lobe of the aedeagus of members of the subgenus Cyclous also present a wide diversity of forms, not seen elsewhere within Dineutini . No other dineutine group exhibits such a suite of sexually selected traits.

Brinck (1955b), but was unsuccessful, resorting to the distinction of African species and American species for the subgenera Protodineutus and Cyclinus respectively. However, our analysis shows Callistodineutus to be nested within the North American species, despite a proposed distinct morphological character, suggesting those utilized by Brinck (1955b) were unsuccessful in identifying large natural groups of