Quadriops Hansen, 1999

Giron, Jennifer C. & Short, Andrew Edward Z., 2021, The Acidocerinae (Coleoptera, Hydrophilidae): taxonomy, classification, and catalog of species, ZooKeys 1045, pp. 1-236 : 1

Genus Quadriops Hansen, 1999 Figs 1P , 2 , 6 , 11C , 48 , 49A-D

Quadriops Hansen, 1999a: 131.

Gender.

Masculine.

Type species.

Quadriops depressus Hansen, 1999a: 136; by original designation.

Diagnosis.

Small to very small beetles, body length 1.6-2.6 mm. Body shape oval in dorsal view; moderate to strongly convex in lateral view, dorsal outline evenly convex or nearly straight along median region (Fig. 48 ). Color orange brown to dark brown, uniform along body regions; ground punctation shallow to moderately marked (Fig. 48 ). Shape of head somewhat rectangular. Frons lateral and posteriorly expanded, forming Tobochares canthus completely dividing eyes in dorsal and ventral portions (Fig. 11C ). Eyes very small in dorsal view. Clypeus laterally expanded in front and around outer margin of eyes; anterior margin of clypeus straight (Fig. 11C ). Labrum partly exposed. Mentum rather smooth and medially depressed; median anterior depression marked by a transverse carina (Fig. 48C, F ). Antennae with nine antennomeres, cupule slightly asymmetric with rounded outline. Maxillary palps rather short and stout, nearly half as long as width of head; maxillary palpomere 4 slightly longer than palpomere 3; inner margin of maxillary palpomere 2 straight to convex, outer margin strongly curved along apical 2/3. Elytra without sutural striae, with punctures either irregularly distributed or forming well defined longitudinal rows; elytra narrowly explanate anteriorly, explanation gradually broader towards apex (Fig. 48 ). Surface of prosternum flat. Posterior elevation of mesoventrite, usually with well-defined transverse ridge, seldom with acute tooth; anapleural sutures concave, separated at anterior margin by distance nearly 0.7 × width of anterior margin of mesepisternum. Metaventrite usually uniformly densely pubescent, sometimes with reduced posteromedian glabrous patch. Protibiae with spines of anterior row hair-like, semi erect, relatively long, and thick; apical spurs of protibia moderately stout, reaching apex of protarsomere 3. All tarsomeres with thick hair-like spines on ventral face of tarsomeres 2-4; metatarsomeres 1-4 similar in length, 5 nearly as long as 3 and 4 combined. Metafemora with tibial grooves moderately developed; anterior surface of metafemora mostly glabrous, with few very scattered small setae (Fig. 48C, F ). Fifth abdominal ventrite apically rounded and without fringe of stout setae. Aedeagus trilobed (Fig. 49A-D ), with basal piece about half length of parameres; median lobe wider than base of each paramere, with narrow, triangular, longitudinal sclerite, usually extending along apical third; parameres as long as, to longer than median lobe, and nearly half as wide; gonopore situated preapically; basal piece with lateral margins straight to sinuate, apically slightly diverging.

Differential diagnosis.

Quadriops is the only known acidocerine with fully divided eyes. Species with uniformly distributed punctures along the elytra may resemble Globulosis , but the moderate punctation of Quadriops is very evident (punctation only shallowly marked in Globulosis ; Fig. 32 ). Some species of Tobochares have nearly divided eyes, and lack impressed striae along the elytra ( Tobochares emarginatus species group, Girón and Short 2021a), resembling species of Quadriops with uniformly distributed punctures along the elytra, but they differ in the shape of the posterior elevation of the mesoventrite (sharply elevated as a tooth or a blunt transverse carina in Quadriops , medially bulging in T. canthus Kohlenberg & Short).

Distribution.

Neotropical: Brazil (Amazonas), Costa Rica, Ecuador, French Guiana, Guyana, Panama, Peru, Suriname, Venezuela; Fig. 6 .

Natural history.

Specimens have been caught using flight intercept traps, many long series have been collected on decaying Clusia fruits, which can be somewhat used as bait (Fig. 10 ). Additional specimens have been collected in rotten logs, sap flows on freshly cut trees, and in the refuse piles of leafcutter ants ( Girón and Short 2017).

Larvae.

The immature stages of Quadriops remain unknown.

Taxonomic history.

Hansen (1999a) described the genus with five species, differentiated mostly by the presence and degree of impression of reticulation on the head and clypeus. When he originally described it, Hansen (1999a) was unsure of the taxonomic affinity of the genus, as the morphology of the lineage was somewhat unusual. He placed it in the Acidocerina (now Acidocerinae ) almost by default as it shared no characters in common with other lineages, but ultimately, he was correct as this placement as verified by Short et al. (2021). García (2000b) described an additional species from Venezuela. The genus was revised by Girón and Short (2017): two species were synonymized with Quadriops depressus Hansen; two new species were described.

Remarks.

Quadriops is the only fully terrestrial genus of Acidocerinae . There are six described species within the genus.

Species examined.

Quadriops acroreius Girón & Short (holotype and paratype), Q. clusia Girón & Short (holotype, paratypes and additional specimens), Q. dentatus Hansen (holotype and additional specimens), Q. depressus Hansen (holotype and additional specimens), Q. reticulatus Hansen (holotype and additional specimens), Q. similaris Hansen (holotype and additional specimens).

Selected references.

Hansen 1999a: original description; García 2000b: description of one additional species from Venezuela; Girón and Short 2017: generic revision including two synonymies and two new species; Short et al. 2021: phylogenetic placement.

Figures

Figure 1. Variation across Acidocerinae, dorsal and lateral views A Colossochares ellipticus B Peltochares sp. C Peltochares conspicuus D Aulonochares tubulus E Helochares sp. F Helochares tristis G Novochares sp. H Helopeltarium ferrugineum I Batochares sp. J Helobata larvalis K Radicitus sp. L Nanosaphes tricolor M Agraphydrus cf. attenuatus N Tobochares luteomargo O Tobochares sulcatus P Quadriops similaris Q Crucisternum ouboteri R Primocerus neutrum S Agraphydrus coomani T Agraphydrus sp. U Globulosis flavus V Crephelochares nitescens.

Figure 2. Phylogeny of the Acidocerinae simplified from Short et al. (2021), indicating the distribution, preferred habitat, and currently described number of species for each genus. For habitat, filled black circles indicate that at least some species of the genus are commonly found in this habitat; light grey circles indicate the genus has been found in this habitat, but is rare or not typical for the group; white circles indicate no species have been recorded for the genus in this habitat.

Figure 6. Known distribution of genera of Acidocerinae: Novochares, Peltochares, Primocerus, Quadriops, Radicitus, Sindolus, Tobochares, and Troglochares.

Figure 10. Examples of terrestrial habitat for Acidocerinae A, B Rotting Clusia fruit, showing Quadriops clusia crawling on the surface (Suriname: SR 17 - 0322 - 03 A) C collecting specimens by submerging rotting fruits in pans of water and waiting for the beetles to float to the surface.

Figure 11. Head of miscellaneous Acidocerinae A-D anterolateral view: A Tobochares luteomargo with white arrow pointing to straight anterior margin of eye B Tobochares emarginatus with white arrow pointing to Tobochares canthus emarginating anterior margin of eye C Quadriops politus with white arrow pointing to Tobochares canthus fully dividing the eye in dorsal and ventral faces D Batochares sp. black arrow pointing to transverse carina on labrum E-L dorsal view of head: E Batochares sp. F Helochares tristis G Crephelochares nitescens, H Chasmogenus australis with black arrow pointing to preclypeal membrane I Colossochares ellipticus J Aulonochares tubulus K Peltochares conspicuus L Helobata larvalis.

Figure 32. Habitus of Globulosis flavus A dorsal habitus B lateral habitus C ventral habitus. Scale bar: 1 mm.

Figure 48. Habitus of Quadriops spp. A-C Q. acroreius: A dorsal habitus B lateral habitus C ventral habitus D-F Q. clusia: D dorsal habitus E lateral habitus F ventral habitus. Scale bars: 1 mm.

Figure 49. Aedeagi of Quadriops, Radicitus and Sindolus spp. A Q. clusia B Q. depressus C Q. reticulatus D Q. similaris E S. sp. (Venezuela) F. S. sp. (Venezuela) G, H R. ayacucho: G dorsal view H lateral view I, J R. cf. granitum (Suriname): I dorsal view J lateral view K, L R. surinamensis: K dorsal view L lateral view. Scale bars: 0.1 mm (A-D); 0.5 mm (E-L).