Revision of the Neotropical water scavenger beetle genus Quadriops Hansen, 1999 (Coleoptera, Hydrophilidae, Acidocerinae)

Abstract The genus Quadriops Hansen, 1999 is revised and redescribed. The genus is found to contain six species, including two that are here described as new: Quadriops clusia sp. n. (Brazil, Guyana, Suriname) and Q. acroreius sp. n. (Suriname, French Guiana). Two species are found to be junior subjective synonyms of Q. depressus Hansen, 1999: Q. amazonensis García, 2000, syn. n. and Q. politus Hansen, 1999, syn. n. The male of Q. similaris Hansen, 1999 is described for the first time. New records are provided for Q. dentatus Hansen, 1999, Q. reticulatus Hansen, 1999, and Q. similaris. All species are described and illustrated in detail. Most species are confirmed as having a terrestrial way of life, with several species being found in rotten fruits, sap flows, and dead wood. Furthermore, we discuss ecological trends of the species given their collecting information.


INBio
Instituto Nacional de Biodiversidad, Santo Domingo, Costa Rica. Morphological methods. Specimens were examined using Olympus SZX7 and SZX16 stereo microscopes (magnifications: 0.8-5.6× with DF PLAPO 1-4× objective lens and 20× eyepieces; 0.7-11.5×, with SDF PLAPO1×PF objective lens and 10× eyepieces, respectively). Genitalia dissections were prepared, in part, by the protocols described by Minoshima et al. (2015), by heating the structures at 60°C in a solution of 10% KOH during 60 minutes. Previous to the KOH treatment, the entire abdomen was removed from the specimen and opened along one side. Afterwards, structures were submerged in glacial acetic acid for 15 minutes, and then rinsed with distilled water. Dissections were performed by placing the cleared parts on a microscope slide with a drop of glycerin. The aedeagi of male holotypes designated by Hansen, originally mounted in Euparal on cards pinned under the specimens, were dismounted by placing the card in 70% alcohol in a water bath (~60°C, 15-20 min) and then observed on a microscope slide with a drop of glycerin.

MALUZ
Images of internal structures were produced by stacking images taken through an Olympus DP72 camera attached to an Olympus BX51 microscope to 200× magnification. Habitus photographs were taken with a Visionary Digital imaging system, using a Canon MP-E 65mm f/2.8 1-5X Macro Lens mounted on a Canon EOS 6D camera body. All final images were created by stacking multiple individual photographs from different focal planes using the software Zerene Stacker. Scanning electron micrographs were taken by using a FEI Versa 3D Dual Beam Scanning Electron Microscope. Specimens were mounted on carbon tape and coated in gold.
Descriptive sequence and morphological terminology largely follows Hansen (1991) except for the use of meso-and metaventrite instead of meso-and metasternum (see Lawrence and Ślipiński 2013). Terms for the ventral surface of head follow Komarek (2004). Terminology for the metafurca follows Velázquez de Castro (1998). Wing venation follows Lawrence and Ślipiński (2013). The generic description has been modified from Hansen (1999).
In the examined material section of the descriptions, the sex of the specimens is indicated only for those in which the genitalia was exposed. For the remainder specimens the sex was not determined.

List of species
Quadriops acroreius sp. n.

Characters of taxonomic portance
For the most part, species of Quadriops are externally homogeneous (at least within the species groups). We also observed very low intraspecific variation, even across large series (hundreds) of specimens. Variation was found mainly in the following characters: Body shape in lateral view. Though the shape of the body in lateral view might be described as subhemispherical, there is interspecific variation in the degree of convexity. The outline of some species can be described as uniformly convex: Q. dentatus, Q. acroreius, Q. reticulatus and Q. clusia (see Figs 1B, F, 3B, F respectively), whereas Q. depressus and Q. similaris are more dorsoventrally flattened (Figs 2B,F).
Coloration. Body coloration, which tends to be uniform across most regions of the beetle, does not represent a diagnostic feature for separating Quadriops species. While coloration in specimens examined ranges from yellowish to reddish to dark brown, this is mostly attributable to intraspecific variation as well as varying degrees of sclerotization. Appendages and the ventral side of the beetles tend to be slightly paler than the dorsal surface of the body.
Microsculpture. One of the main characters used by Hansen (1999) to differentiate species was the presence, density and extension of microreticulations on the head, frons, and pronotum. Even if it might be useful in recognizing particular species (e.g. Q. acroreius vs. Q. dentatus), by looking at series of specimens, it is a variable character that should not be considered exclusively diagnostic.
Elytra. Two main groups of species can be distinguished according to the distribution of the ground and serial punctures of the elytra: those in which the punctures are randomly and uniformly distributed over the surface (Q. acroreius and Q. dentatus, see Fig. 1), and those in which the punctures are serially arranged, forming well defined longitudinal striae (see Figs 2 and 3). With the exception of Q. clusia, in striate species the punctures along the striae are clearly larger than those on the interstria (in Q. clusia all elytral punctures are similarly large; see Fig. 6). In addition, the elytral punctures can be simple as in Q. clusia (Fig. 6A) or possess microincisions that radiate from the margins of the puncture (ramified punctures) as in Q. reticulatus (Fig. 6B).
Mesoventrite. In Quadriops, the mesoventrite is broadly elevated posteriorly. The wide elevation usually has a transverse ridge, which varies in shape and sharpness. In the known species with irregularly distributed elytral punctures, the transverse ridge is strongly produced. It forms a blunt, vertical, median tooth in Q. dentatus, whereas in Q. acroreius it forms a wide, transverse, straight and blunt carina. As for species with elytral punctures aligned into striae, the transverse ridge can be simply curved, slightly angulate or bisinuate. For this group of species, the shape of the transverse ridge exhibits more intraspecific variation, and is not consistent within series of specimens.
Aedeagus. The general shape of the aedeagus and the length ratio between the basal piece and the median lobe + parameres is generally consistent within species. There is both inter-and intraspecific variation in the outer margins of the basal piece and the shape of the outer margins and apex of the parameres. The gonopore is positioned at the apex of the median lobe, but its shape exhibits intraspecific variation. The shape of the apices of both the median lobe and the parameres tend to be consistent within species. It is important to highlight that some differences observed in the aedeagi presented here may be a result of incomplete clearing, owed to positioning during the photographing process, and/or product of imperfect focus from the stacking process.
Description. Body broadly oval, weakly convex, with dorsum distinctly flattened in some species. Head. Eyes completely divided into dorsal and ventral faces by lateral canthus of the frons; dorsal face of eye tear-drop shaped, smaller in size relative to the ventral face. Antennae (see Fig. 4A) with 9 antennomeres, usually paler than general coloration of head; antennomere 1 reaching midpoint of ventral face of eye (reaching cardo-stipes joint), nearly 1.5-times longer than antennomere 2; antennomere 3 nearly as long as antennomeres 4-5 combined; antennomere 6 forming a rather small, but well differentiated cupule, antennomeres 7-9 similar in size, slightly flattened, forming a loosely articulated, pubescent club; setae at apex of antennomere 9 longer than general pubescence of club. Temporae forming a rather flat surface behind the eyes, densely covered by setae (hydrofuge pubescence, see Fig. 4B). Frons and clypeus (see Fig. 4A, C) with ground punctures uniformly distributed over the surface, accompanied by scattered seta-bearing systematic punctures; setae particularly noticeable on frons anterior to the eye, including lateral canthus, and behind frontoclypeal suture; surface between punctures ranging from smooth to finely reticulated, especially on anterior region of clypeus; anterior corners of clypeus widely rounded; anterior margin of clypeus usually emarginate medially, with distinct bead along entire margin. Labrum reduced, paler, rather short and wide, sometimes appearing deflexed and concealed by clypeus from above (see Fig. 4C); dorsal surface convex and finely reticulated; anterior margin mesally widely emarginate and bent inwards; lateral margins bearing a row of long setae. Maxilla (see Fig. 4A) usually with sparse setae on ventral surface of cardo and stipes, with a row of stiff decumbent spiniform setae along outer dorsal margin of palpifer; maxillary palps yellowish, shorter than antennae, and somewhat stout; palpomeres similar in size; palpomere 1 shorter than stipes, with inner margin straight, and outer margin distally strongly convex; palpomere 2 conical (narrower at base), with inner margin convex at base and outer margin widely convex; palpomere 3 digitiform, rather elongate (compared to 1 and 2), apically somewhat truncate; apex of palpomere 3 bearing sensilla. Mandibles with apex bifid (examined in Q. clusia and Q. reticulatus). Labial palps yellowish, nearly as long as mentum, dorsoventrally flattened; palpomere 2 with inner margin straight, and outer margin distally strongly convex, with a long seta on outer apical corner; palpomere 3 digitiform, usually shorter and markedly narrower than palpomere 2, with a subapical seta on outer corner. Mentum nearly 1.5-times wider than long, parallel sided, moderately to strongly depressed anteromedially; anterior margin with relatively deep median excision, limited from the ventral surface by a U to V shaped transverse carina. Submentum rather flat; ocular ridge (see Komarek 2004, Fig. 1) well developed (see Fig. 4A). Thorax. Pronotum widest at base, narrowed anteriorly, surface rather evenly convex; ground punctation uniform, moderately fine, sometimes ground punctures connected by fine lines; seta bearing systematic punctures scattered through the surface, particularly noticeable as transverse anterolateral bands. Scutellum of moderate size, triangular, nearly as long as wide. Prosternum ( Fig. 5A) well developed, flat, at most only weakly convex, not carinate; anterior margin of prosternum only slightly convex mesally; intercoxal process somewhat triangular (with base facing posteriorly), with surface posteriorly bifurcated. Mesoventrite not fused to mesepisterna, narrowly reaching anterior mesothoracic margin, posteriorly widely elevated; elevation usually with a transverse ridge, variable in shape and sharpness (in Q. dentatus the ridge is produced into a blunt, vertical, median tooth); mesepisternum obliquely widely concave. Mesofurca (examined in Q. clusia and Q. reticulatus; see Fig.  5B) with short arms, hardly as long as the length of mesocoxae; apex of arms triangular to irregularly explanate. Metaventrite weakly convex, medial posterior portion rather flat, entire metasternum very finely and densely pubescent, without median glabrous patch (reduced in Q. acroreius and Q. dentatus). Metepisterna approximately three times longer than wide, parallel-sided. Metafurca (examined in Q. clusia and Q. reticulatus; see Fig. 5C) short and stout, with furcal arms slightly longer than stalk; stalk somewhat triangular (wider near the crux, gradually narrowing distally); outer margins of stalk diverging from base towards midpoint of furcal arms; furcal arms somewhat rectangular, with apex (hemiductus) explanate, obliquely positioned; anterior tendons inserted near midpoint of dorsal edge of furcal arms; dorsal sheaths well developed, as wide as to slightly wider than widest point of lateral sheaths. Elytra. Surface even (without elevations or depressions), with 10 well defined longitudinal rows of serial punctures (see Fig. 6) (except in Q. acroreius and Q. dentatus which have irregularly punctate elytra; see Fig. 1), sutural series rather sharply impressed posteriorly, the remaining series slightly impressed; seta bearing systematic punctures scattered along interstriae; elytral margins slightly explanate anteriorly, increasing to more broadly explanate in posterior third. Epipleura well developed, densely covered by pubescence, rather weakly oblique, relatively wide anteriorly, gradually narrowing towards level of metacoxae, continued as a somewhat narrow stripe to apex; pseudepipleura glabrous, relatively wide throughout, only slightly narrowed posteriorly; surface of pseudepipleura smooth, undulated, anteriorly reticulate or posteriorly canaliculate. Wings (see Hansen 1999, fig. 17;Lawrence and Ślipiński 2013, Fig. 23; examined in Q. clusia and Q. reticulatus) nearly three times longer than wide; radial cell as a pigmented, somewhat triangular area at anterior margin, positioned near mid length of wing; r4, RA 3+4 and RA 3 reduced; RA 3+4 not connected to radial cell; RP 2 reduced to a pigmented wide stipe; MP 3+4 , CuA 2 and AA 3 reaching margin of wing; basal cell long, reaching a little more than halfway towards posterior wing margin; wedge cell absent; anal (jugal) lobe well developed, narrow, demarcated from remainder of wing by a sharp excision at posterior wing margin. Legs. Pro-and mesofemora with dense pubescence, at most in about basal half, remainder of surface glabrous and shiny, with subtle reticulations; posterior femora mostly glabrous on ventral face, with only scarce scattered long setae over the surface, sometimes with reduced anterobasal, pubescent patch; all femora with rather sharp tibial grooves on inner face except basally. Tibiae moderately slender, rather weakly flattened, with moderately fine and sparse spines. All tarsi with five tarsomeres, bearing 2 (tarsomeres 2-4) to a few (tarsomere 5) long apical hair-like setae on dorsal face; tarsomere 5 without setae or spines on ventral face, tarsomeres 1-4 similar in size and shape; pro-and mesotarsi similar in size and proportions, tarsomeres 1-4 with moderately long and rather dense spiniform setae on ventral face, tarsomere 5 approximately as long as tarsomeres 1-4 combined; meta tarsi 1.3 times longer than pro-and mesotarsi, with tarsomeres 1-4 with 1-2 pairs of spines on ventral face, tarsomere 5 approximately as long as tarsomeres 2-4 combined; claws rather large, moderately curved. Abdomen. Abdomen with 5 ventrites, flat or very weakly convex, all ventrites with uniform, very fine and dense pubescence; first ventrite without median carina, posterior margin of fifth ventrite simply rounded. Aedeagus (Figs 7,8) with basal piece about half the length of parameres; median lobe wider than base of each paramere, with a narrow, triangular, longitudinal sclerite, usually extending along apical third; parameres as long as, to longer than median lobe, and nearly half as wide; gonopore preapically situated; basal piece with lateral margins straight to sinuate, apically slightly diverging Larvae: The immature stages are unknown. Biology. Extensive collecting data as well as field observations confirm that the genus is terrestrial. While many specimens have been caught using flight intercept traps, many long series have been collected on decaying Clusia fruits. Additional specimens have been collected in rotten logs, sap flows on freshly cut trees, and in the refuse pile of leafcutter ants. The genus has never been collected from aquatic or semiaquatic habitats. It has been found at elevations from 30 to 1600 m. Q. acroreius, Q. dentatus and Q. similaris are not found higher than 350 m, whereas Q. reticulatus is usually found higher than 1000 m.  Differential diagnosis. Quadriops acroreius is very similar to Q. dentatus, both species being moderately convex (as opposed to dorsally flattened) and the serial punctures of the elytra are randomly and uniformly distributed, not aligned to form welldefined longitudinal rows. It can be easily distinguished by the shape of the elevation of the mesoventrite, which is a wide, transverse, straight carina (as opposed to a toothlike projection as in Q. dentatus); in addition, the surface of head and clypeus between punctures is smooth (as opposed to reticulated).
Description. Body length 1.9-2.0 mm, width 1.2-1.3 mm. Body elongate oval, moderately convex. General coloration uniform dark brown. Surface of pronotum and elytra, smooth (as opposed to reticulated between punctures), only slightly reticulated on head and clypeus. Elevation of mesoventrite forming a wide, transverse, straight, blunt, strongly raised carina. Metaventrite with a postero median semi triangular glabrous area. Elytra with randomly and uniformly distributed punctures, not aligned into striae; surface of pseudepipleura anteriorly reticulated, posteriorly smooth. Metafemora with basal 1/8 covered by pubescence.
Etymology. Named from the Greek "akroreia", meaning mountain ridge (Brown 1956) Differential diagnosis. Quadriops clusia has well defined longitudinal rows of serial punctures (as opposed to uniform and randomly distributed as in Q. acroreius and Q. dentatus, see Fig. 1). The serial punctures on the striae are simple and similar in size as those on the interstria (Fig. 6A) (as opposed to ramified and conspicuously larger than the punctures on the interstrial surface, as on the remainder species, see Fig. 6B). Transverse ridge on the elevation of the mesoventrite rather blunt, and slightly bisinuate.
Description. Body length 2.1-2.5 mm, width 1.2-1.4 mm. Body elongate oval, moderately and evenly convex. General coloration reddish brown, with pronotum and clypeus only slightly paler. Surface of head, frons and pronotum reticulated. Clypeus with anterior margin nearly straight. Elevation of mesoventrite with transverse ridge rather broad, and slightly bisinuate. Elytra with ten well defined longitudinal rows of serial punctures; punctures on the interstrial surface similar in size to serial punctures (Fig. 6A); surface of pseudepipleura anteriorly undulated, particularly at limit with epipleura, posteriorly smooth. Metafemora with pubescence only along articulation with trochanter, and sometimes along proximal 1/6 of anterior margin. Aedeagus (Figs 7I-K) with parameres as long as median lobe, and nearly as wide at apical 1/4; parameres with outer margins nearly straight, only slightly curved inwards at apical 1/3; apical 1/3 of inner margin of parameres concave; apical 1/3 of parameres rather digitiform and straight, parallel to longitudinal axis of aedeagus. Median lobe with lateral margins straight, converging towards the apex; apex of aedeagus widely rounded; gonopore rather semicircular. Basal piece as long as 0.5-times the length of the median lobe, with lateral margins straight; manubrium 0.5 times the length and nearly as wide as the base of basal piece.
Etymology. Named after Clusia, the genus of plants on whose decomposing fruits the beetles have been collected.
Variation. There is slight variation in the proportions of the aedeagus. Some specimens might have a comparatively wider median lobe (Fig. 7K), or seem more slender overall (Fig. 7J).
Distribution. Brazil (Amazonas), Guyana, Suriname. See Fig. 9B. Biology. Most known specimens have been collected on rotten fruits of Clusia trees, sometimes in series of many hundreds of individuals. In Guyana, this species was found on and beneath rotten fruits of Clusia grandiflora (Fig. 10A-B). In Suriname, this species was collected on and beneath the rotten fruits of several Clusia species, including C. grandiflora and C. cf. nemorosa (Fig. 10C-D). The beetles appear most common on fruits in a stage of decay where they are soft and sticky (as opposed to more advanced stages of decay in which the fruits become dry or crumbly). The beetles were also present in leaves beneath the decaying fruits into which rotting fluids had seeped. Most specimens were collected by collecting these fruits and submerging them in pans of water, at which time the beetles float to the surface. We collected hundreds of specimens on several occasions using this method. However, not all rotten Clusia patches we examined (some even within 1 km of other patches with Quadriops abundance) contained many or any Quadriops specimens. We sifted general forest litter and did extensive aquatic collecting at sites in Guyana and Suriname where we found abundant Quadriops clusia populations, but no specimens were ever found in these habitats. We also laid baits of other fruits including bush cashews and bananas but these were not successful in attracting Quadriops. We believe the habitat of this species is likely restricted to rotten fruits, and possibly only those from Clusia. Quadriops clusia has been collected at elevations between 500 and 700 m.

Quadriops dentatus Hansen, 1999 Figs 1A-D, 9B
Quadriops dentatus Hansen, 1999: 134. Differential diagnosis. Quadriops dentatus is very similar to Q. acroreius, both species being moderately convex (as opposed to dorsally flattened) and the serial punctures of the elytra are randomly and uniformly distributed, not aligned to form well defined longitudinal rows. It can be easily distinguished by the toothlike projection of the mesoventrite (as opposed to a wide, transverse, straight, blunt carina as in Q. acroreius); in addition, the surface of head and clypeus is smooth between punctures (as opposed to reticulated).
Redescription. Body length 1.6-2.2 mm, width 1.1-1.2 mm. Body elongate oval, moderately convex. General coloration uniform yellowish to dark brown. Surface smooth (as opposed to reticulated between punctures) on head, pronotum and elytra. Elevation of mesoventrite forming a basally transverse acute tooth. Metaventrite with a posterior, short, glabrous and narrow stripe. Elytra with randomly and uniformly distributed punctures, not aligned into striae; surface of pseudepipleura smooth throughout, at most only slightly reticulated at base. Metafemora with pubescence only along dorsal area of articulation to trochanter.
Variation. There is variation in size with the type specimen being the largest. Fig. 9B.

Distribution. Venezuela (Bolívar), Suriname (Sipaliwini), French Guiana (Matoury, Roura). See
Biology. The male of this species remains unknown. All known specimens were collected using flight intercept traps, at elevations between 50 and 350 m. Differential diagnosis. Quadriops depressus is externally very similar to Q. similaris, and Q. reticulatus, as all have well defined longitudinal rows of serial punctures (as opposed to uniform and randomly distributed as in Q. acroreius and Q. dentatus, see Fig. 1), and the serial punctures are conspicuously larger than the punctures on the interstrial surface (as opposed to similarly large as in Q. clusia, see Fig. 6). It can be separated from Q. reticulatus by the dorsal outline of the body being nearly flat (as opposed to moderately convex), and the surface of the pseudepipleura posteriorly markedly canaliculated (see Fig. 2C; as opposed to smooth). Quadriops depressus can be distinguished from Q. similaris by the rounded shape of the apex of the parameres (see Fig. 7 A-D; as opposed to angulate, as in Fig. 8).

Quadriops depressus Hansen, 1999
Redescription. Body length 2.1-2.5 mm, width 1.3-1.4 mm. Body elongate oval, moderately convex, with dorsal outline nearly flat. General coloration reddish to dark brown, with pronotum and clypeus only slightly paler. Surface of clypeus smooth to reticulated, usually smooth on frons and pronotum. Elevation of mesoventrite with transverse ridge rather fine and curved (posteriorly concave). Elytra with ten well defined longitudinal rows of serial punctures; punctures on the interstrial surface noticeably smaller than serial punctures; surface of pseudepipleura anteriorly undulated, particularly at limit with epipleura, posteriorly reticulated. Metafemora with pubescence only at base of anterior margin at most. Aedeagus (Figs 7A-D) with parameres slightly longer than median lobe; parameres with outer margins nearly straight, only slightly curved inwards at apical 1/3; apical 1/3 of inner margin of parameres concave; apical 1/6 of parameres digitiform, with rounded apex slightly directed towards longitudinal axis of aedeagus. Median lobe with lateral margins straight, slightly converging from base; apex of aedeagus widely rounded; gonopore rather semicircular. Basal piece as long as 0.4-times the length of the median lobe, with lateral margins straight; manubrium 0.5-times the length and clearly narrower than the base of basal piece.
Variation. There is variation on the density and presence of reticulation on the surface of the frons and clypeus.

Quadriops reticulatus Hansen, 1999
Redescription. Body length 2.0-2.4 mm, width 1.2-1.45 mm. Body elongate oval, moderately convex, with dorsal outline only slightly flat. General coloration reddish to dark brown, with margins of pronotum and clypeus only slightly paler. Surface of clypeus, frons and pronotum reticulated. Elevation of mesoventrite with transverse ridge rather fine and curved (posteriorly concave). Elytra with ten well defined longitudinal rows of serial punctures; punctures on the interstrial surface noticeably smaller than serial punctures; surface of pseudepipleura anteriorly undulated, particularly at limit with epipleura, posteriorly smooth. Metafemora with pubescence only on anterior basal corner. Aedeagus (Fig. 7E-H) with parameres as long as or longer than median lobe; parameres with outer margins slightly concave near midlength; apical 1/3 of inner margin of parameres concave; apical 1/3 of parameres digitiform, rather narrow, with rounded apex, slightly pointing towards longitudinal axis of aedeagus. Median lobe with lateral margins usually straight and clearly converging from base; apex of aedeagus widely rounded; gonopore variable in shape. Basal piece as long as 0.5 to 0.7-times the length of the median lobe, with lateral margins straight to sinuate; manubrium 0.3 to 0.6-times the length and clearly narrower than the basal piece at its base.
Variation. The degree of sharpness of the transverse ridge of mesoventrite varies from being blunt and moderately marked to sharp. There is variation on the shape of the aedeagus, even though the overall shape is conserved across the species. Specimens from Panama tend to be smaller.
Biology. Most known specimens have been collected by using flight intercept traps. A few specimens were collected from "fungusy logs". Additionally, a disassociated note at INBio about one collecting event of Quadriops in Costa Rica indicated a series had been collected on the sap of freshly cut trees. Most Q. reticulatus specimens have been collected at elevations between 1000 and 1600 m.
Remarks. The female specimen from the Darién of Panama has a differently shaped transversal ridge of the mesoventrite, but no other characters were found to differentiate it from Q. reticulatus. However, when males are found it may be shown to represent a distinct species. Several specimens were also observed to have mites on the dorsal surface of the elytra.  longitudinal rows of serial punctures; punctures on the interstrial surface noticeably smaller than serial punctures; surface of pseudepipleura anteriorly undulated, posteriorly markedly canaliculated. Metafemora with pubescence only along proximal 1/5 of anterior margin. Aedeagus (Fig. 8) with parameres usually longer than median lobe; parameres with outer margins straight to slightly convex along basal 3/4, then distinctly curved inwards at apical 1/4, or gradually curved from midlength; preapical area of inner margin of parameres concave; apex narrowly rounded, forming an acute angle pointing towards apex of aedeagus. Median lobe with lateral margins straight to somewhat sinuated, either parallel along basal 2/3 or converging from base; apex of aedeagus variable, wide to narrow, angulated to rounded; gonopore usually semicircu- Figure 10. Habitat of Quadriops clusia sp. n.: A Clusia cf. grandiflora on the forest floor, collecting event GY14-0312-04A B A specimen of Quadriops clusia sp. n. crawling on the surface of a rotting Clusia fruit, collecting event GY14-0312-04A C Clusia cf. nemorosa in Brownsberg Nature Park, Suriname on which Quadriops clusia sp. n. was collected D Collecting Quadriops and other terrestrial hydrophilid specimens by submerging collected rotting Clusia fruits in pans of water and waiting for the beetles to float to the surface, collecting event SR17-0322-03A. lar. Basal piece as long as 0.6-times the length of the median lobe, with lateral margins straight to sinuate; manubrium 0.3 times the length and clearly narrower than the basal piece at its base.

Quadriops similaris
Variation. There is variation in the shape and sharpness of the transverse ridge; the general shape of the aedeagus is consistent within the species, but varies in specific characters: shape of outer margins of parameres, width and shape of apex of parameres, shape of apex of aedeagus. There is one male specimen from Suriname (Collecting event SUR1F99 070; see Fig. 8H) in which the median lobe is longer than the parameres and the gonopore is rather oval.
Biology. Most specimens were collected in flight intercept traps. The species was also collected on the refuse pile of the ant Acromyrmex hystrix, under fermenting bark and by fogging a splintered tree trunk. Q. similaris has been collected at elevations between 25 and 350 m.
Remarks. The male of Q. similaris was unknown until now. Specimens collected in Guiana were recognized as belonging to this species by the posteriorly markedly canaliculated pseudepipleura, a character shared with Q. depressus. There are no consistent external characters that distinguish both species, but the shape of the apex of the parameres is remarkably different.

Key to the species of Quadriops Hansen, 1999
1 Elytra with punctures randomly and uniformly distributed (see Fig. 1 Vanessa Kadosoe (NZCS), and Paul Ouboter (NZCS), as well as the curators of the collections listed above for the loan of valuable specimens. Angel Solis and Jack Longino assisted AEZS on visits to review material at INBIO and ALAS (La Selva) respectively. This study was supported by US National Science Foundation grant DEB-1453452 to AEZS. Some fieldwork in Suriname and Guyana was partly funded by Conservation International and WWF-Guianas respectively.