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A review of the Cercyon Leach (Coleoptera, Hydrophilidae, Sphaeridiinae) of the Greater Antilles

Abstract The representatives of the genus Cercyon Leach occurring in the Greater Antilles are reviewed. Ten species are recorded, of which five are described here as new: C. gimmeli sp. n. (Dominican Republic), C. armatipenis sp. n. (Dominican Republic), C. taino sp. n. (Dominican Republic), C. sklodowskae sp. n. (Jamaica) and C. spiniventris sp. n. (Dominican Republic). Diagnoses and detailed distributional data are also provided for C. floridanus Horn, 1890 (distributed in southeastern United States of America and Cayman Islands), C. insularis Chevrolat, 1863 (endemic to the Antilles) C. praetextatus (Say, 1825) (widely distributed in the New World incl. Greater Antilles), C. quisquilius (Linnaeus, 1761) (an adventive species of Paleartic origin) and C. nigriceps (Marshall, 1802) (an adventive species probably of Oriental origin). Cercyon armatipenis, C. gimmeli, C. taino form a group of closely related species only distinguishable by male genitalia and DNA sequences. A key to the Great Antillean Cercyon is provided and important diagnostic characters are illustrated. The larvae of C. insularis and C. taino were associated with adults using COI barcode sequences, illustrated and diagnosed. Full occurrence data, additional images and COI barcode sequences were submitted to open access on-line depositories in an effort to provide access to complete data.


Introduction
Until very recently, water scavenger beetles (Hydrophilidae) from the Greater Antilles in the Caribbean Region were largely neglected and systematic or faunistic studies were scarce. For instance, 46 of 56 hydrophilid species recorded from Cuba were described in the 18 th and 19 th centuries (Peck 2005). Nevertheless, recent taxonomic studies have brought to light many new species and new country records in this region e.g. in genera Berosus Leach (Deler-Hernández et al. 2013a), Enochrus Thomson (Deler-Hernández and Delgado 2010;Short 2005), Oosternum Sharp (Deler-Hernández et al. 2014), Phaenonotum Sharp (Deler-Hernández et al. 2013b) and Tropisternus Solier (Spangler and Short 2008). However, many other groups still await a comprehensive treatment, which includes Cercyon, the most speciose genus within the subfamily Sphaeridiinae. As with most members of the subfamily, Cercyon species have predominantly terrestrial habits, and are frequently associated with decaying plant material and feces. Approximately 260 species have been described from all zoogeographical zones (Short and Fikáček 2011), of which 24 have been recorded from Central and South America (Hansen 1999;Fikáček 2006). The number of described species seems highly underestimated in the Neotropical Region, due to the lack of recent taxonomic work. The most comprehensive identification resource for Central American fauna still remains the iconic Biologia Centrali-Americana (Sharp 1882(Sharp , 1887. The situation is also aggravated by the presence of introduced Old World synanthropic species, which are difficult to recognize and are sometimes confused with native species (Fikáček 2009).
Six species of Cercyon have been recorded from the Greater Antilles: the Cuban-endemic C. insularis Chevrolat whose identity has remained unclear (Hansen 1999;Peck 2005), two species widely distributed in the New World (Cercyon variegatus Sharp, Cercyon praetextatus (Say); Leng and Mutchler 1917;Smetana 1984;Fikáček 2009), one species native to southeastern United States of America (Cercyon floridanus Horn; Thomas et al. 2013) and two widely distributed adventive species (Cercyon nigriceps Marsham, Cercyon quisquilius (Linnaeus); Leng and Mutchler 1917;Fikáček 2009). Our recent field work and examination of museum material revealed that additional species occur in the area, which provided the impetus for this study. In order to provide a review that will constitute a reliable reference for future studies on the genus Cercyon and the tribe Megasternini, we complemented the traditional taxonomic account with COI sequences (i.e., "DNA barcodes"), complete occurrence data, and full set of highresolution photographs, all deposited in online freely available platforms.

Material and methods
Examined specimens and depositories. A total of 848 specimens of Cercyon from the Greater Antilles were examined, including the type specimens of Cercyon insularis Chevrolat and C. variegatus Sharp. Label data are only reproduced verbatim for type specimens; each individual label is separated by double slash "//"; notes on the label data or additional information are written between square brackets [ ]. All holotypes are marked with red label bearing the following text: "HOLOTYPE, Cercyon [name of the species] sp. n., Arriaga-Varela, Seidel, Deler-Hernández and Fikáček des. 2016". All paratype specimens are marked by yellow label bearing the following text: "PARATYPE, Cercyon [name of the species] sp. n., Arriaga-Varela, Seidel, Deler-Hernández and Fikáček des. 2016". A georeferenced dataset of the studied specimens is available as Excel spreadsheet in Suppl. material 1. The file only includes specimens identified to species. The distribution maps  were constructed from the GPS data extracted from the Excel spreadsheet and mapped using the R script (see Suppl. material 4).
The examined specimens are deposited in the following collections: were adapted in Adobe Photoshop CS6. All original pictures including additional views not presented in this paper are published and freely available on Flickr in order to serve for further morphological studies. DNA barcoding. Most of the examined specimens were collected during recent expeditions to Cuba, Dominican Republic and Puerto Rico. Samples were preserved in 96% ethanol and stored at -20 °C. DNA was extracted from complete specimens using a QiaGen Blood and Tissue DNA extraction kit following the manufacturer's instructions. The highly variable 5' region of the mitochondrial cytochrome c oxidase subunit I gene (COI) was amplified using LCO1490 (5'-GGTCAACAAATCATAAAGATATTGG-3') and HCO2198 (5'-TAAACTTCAGGGTGACCAAAAAATCA-3') primers (Folmer et al. 1994). Each 10 µl PCR reaction contained 6.7 µl H 2 O, 0.4 µl of MgCl 2 (25 mM), 0.2 µl of dNTPs (10 mM), 0.3 µl of each forward and reverse primer (10 µM), 0.1 µl of Taq polymerase (5 u/µl), 1.0 µl of 10x Taq buffer, and 1.0 µl of DNA template. The PCR conditions consisted of 3 min at 94 °C + 35 cycles of 30 s at 94 °C, 45 s at 48 °C and 1 min at 72 °C + 8 min at 72 °C. 5 µl of each PCR product were purified by adding 0.5µl (20 u) Exonuclease I (Exo1) and 1µl (1 u) Thermosensitive Alkaline Phosphatase (FastAP) (Thermo Fisher Scientific) and incubating the mixture for 15 min at 37°C, followed by 15 min at 80°C. The Sanger sequencing was performed by BIOCEV (Vestec, Czech Republic) on a capillary DNA sequencer. Sequences were edited with Geneious 9.1.4. We did not attempt DNA extraction and sequencing of old museum specimens, which is why we only provide sequences for six of the ten species occurring in Greater Antilles.
Analyses of molecular data. In order to identify the larvae collected along with adult specimens, a maximum likelihood analysis of obtained COI sequences was performed. We combined the newly generated sequences of freshly collected adults and larvae, and combined them with additional sequences of two introduced species (C. quisquilius and C. nigriceps from Europe and Canada) from the Barcode of Life Data Systems (BOLD; http://www.boldsystems.org). Sequences were aligned using the ClustalW algorythm in Geneious 9.1.4. The final alignment had a length of 610 bp and was tested for the best nucleotide substitution model using MEGA7 (Kumar et al. 2016). A phylogenetic analysis using the maximum likelihood algorythm and 1000 bootstrap replicates was performed in the same software.

Open access to complete data
This taxonomic paper includes only a part of the data accumulated in the course of our study. Part of the primary data (e.g., unedited photographs, the complete set of unedited SEM micrographs, DNA sequences, spreadsheet-fomatted species distribution data) are not included here. To make all primary data accessible, we deposited them to open access on-line depositories as specified below. For more details about biodiversity data publishing, see e.g. the policies and guidelines implemented for Pensoft Publishers (Penev et al. 2011).
Species distribution data. The distribution data on all specimens examined are presented in unstructured text format directly in the paper. The conversion of these data into a structured, computable format (as XML, so called parsing) is difficult, and no algorithm exists for parsing occurrence records (see Sautter and Böhm 2014 for the analogous problem of parsing literature references).
The text-formatted distribution data published here are, however, based on a structured Excel spreadsheet following the Darwin Core (henceforth DwC) format for biodiversity data described by Wieczorek et al (2012). DwC defines how the data should be structured (i.e. which columns may be included in the table, how they should be called and which part of the data they should include). In some cases DwC also specifies the format of the entries (e.g., how date should be formatted). Details are available through the website of the Biodiversity Information Standards (TWDG; http://rs.tdwg.org/dwc/terms/). Being a formal biodiversity standard, DwC is nowadays used by a wide spectrum of on-line biodiversity portals, e.g. by the Global Biodiversity Information Facility (GBIF), Encyclopedia of Life, and the Atlas of Living Australia. This is the reason why we selected it. The Excel file is attached here as Suppl. material 1, it is included in the .zip file submitted to Zenodo, and was used for the GBIF submission.
The Publication of distribution data to GBIF is possible through the institution or organization, which is a member or partner of GBIF (direct submissions from individual users are not possible) using the Integrated Publishing Toolkit (IPT). IPT allows to upload the distribution data from the DwC-formatted Excel spreadsheet, specify the metadata about the dataset, and publish the data to the GBIF portal. We submitted our data through Pensoft as an organization associated with GBIF using the Pensoft IPT Data Hosting Centre (http://ipt.pensoft.net/). DNA data and voucher information. The cytochrome oxidase I barcode sequences and the data about the voucher specimens were submitted to the Barcode of Life Data Systems (BOLD; http://www.boldsystems.org/) using the user web interface available after registration. The submission requires first the submission of the specimen data using the Excel-based spreadsheet following the Specimen Data Submission Protocol (http://www.boldsystems.org/index.php/resources/handbook?chapter=3_submissions.html&section=data_submissions). To prevent the re-typing of the specimen data again, we wrote an R script converting the data from DwC to the format required for BOLD submissions (see Suppl. material 3). Once specimen data are submitted, all other information (voucher photos, DNA sequences, DNA trace files) can be submitted, using the identification code (SampleID) to connect the data to the respective voucher specimen. We submitted the sequences under Process ID GANTC001-16 and GANTC002-17 to GANTC015-17 in BOLD.
Original photo-documentation. The original photo-documentation includes the unedited high-resolution versions of photos and SEM micrographs that we used in this publication, plus many photos and SEM micrographs that were taken for comparative purposes but are not published here. We submitted all these files to Zenodo as a part of the .zip file containing all our primary data. Since the images are not easy to see in this way, we also submitted all photos to Flickr photo hosting service where they can be easily displayed; they are available at https://www.flickr.com/photos/142655814@ N07/collections/72157678126129411/.

Diagnosis.
Cercyon can be distinguished from other hydrophilid genera occurring in the Greater Antilles by the following combination of characters: antenna with compact club; prothorax with conspicuous antennal groove not reaching pronotal margin; medial part of prosternum not demarcated from lateral parts; metaventrite without arcuate lines in anterolateral corners; mesoventral plate fusiform, narrowing anteriorly and posteriorly, touching anterior margin of metaventrite in one point. Cercyon species are very similar to the members of Pelosoma, a Neotropical genus that is recorded from the Lesser Antilles; Pelosoma differs from Cercyon by the mesoventral plate widely contacting the metaventrite (it only narrowly contacts it in Cercyon). Small species of Cercyon may resemble the members of Oosternum, which can be easily distinguished from Cercyon by possessing a metaventrite with an arcuate ridge delimiting its anterolateral corner, and in some species also by elevated median part of the prosternum. Metaventrite with raised pentagonal area markedly wide at midlength, 0.6× as long as wide (Fig. 13f )  Pronotum uniformly light brown, elytra more or less uniformly greyishbrown (Fig. 3a). First abdominal ventrite of females ( Fig. 11h) with longitudinal carina prolonged into an acute spiniform setose process; longitudinal carina of male first abdominal ventrite not projected. Raised area of metaventrite comparatively wide, 0.8× as long as wide (Fig. 11g)  Prosternum with median ridge forming a small rounded to weakly pointed process (Fig. 10c). Raised median area of metaventrite reaching anterior margin of metaventrite (Fig. 10g). Anterior margin of mentum emarginate medially (Fig. 10a). Apex of fifth abdominal ventrite with a triangular bulged projection in females (Fig. 10i) Median lobe blunt at apex (Fig. 5c, k); parameres as long as or longer than phallobase (Fig. 5a, i)  Median lobe wide basally, narrowing apically, with large gonopore and many spines in apical fifth ( Fig. 5j-k); parameres ca. as long as phallobase (Fig. 5i)

Cercyon gimmeli species group
This species group is composed of three very closely related species endemic to the island of Hispaniola. Specimens are indistinguishable on the basis of external morphology and can be only told apart by examination of male genitalia. At least in one locality, two species of this group were collected syntopically. For this reason, we refrain from using female specimens as paratypes unless the specimen was associated with males by DNA barcode, and female specimens are not listed in the text below neither in the DarwinCore spreadsheet submitted to GBIF for that reason. Below, we provide a diagnosis allowing to separate all species of the species group from other Cercyon species. Further on, we describe Cercyon gimmeli sp. n. in full, and provide only comparative diagnoses for the other two species, C. armatipenis sp. n. and C. taino sp. n. Diagnosis of the Cercyon gimmeli species group. Members of the species group can be differentiated from other Greater-Antillean Cercyon by the following combination of characters: size 2.8-3.5 mm; dorsal surface of head black, with yellowish anterolateral margins of clypeus; pronotum black with sharply defined creamywhite areas at lateral margins; elytra black, with large, pale, rather sharply defined spot in posterior third of both elytra (Fig. 1); anterior margin of mentum not emarginated (Figs 8a, 9a, f ); medial ridge of prosternum anteriorly forming a rounded knob (Figs 8c, 9g); mesoventral plate narrow, ca. 5.7× as long as wide (Figs 8f, 9c, h); metaventrite (Figs 8g, 9c, h) without femoral lines, with narrow raised pentagonal area, 1.1× as long as wide; first abdominal ventrite without spine-like process in both sexes (Fig. 8h); metatibia slightly bent outwards; apex of fifth abdominal ventrite without an apical triangularly bulged projection in both sexes (Fig. 8i).
By the dorsal coloration, the species of C. gimmeli group could be confused with C. praetextatus (Say), C. floridanus Horn and C. sklodowskae sp. n. However, they can be easily distinguished from from C. praetextatus and C. floridanus Horn by the distinctly narrower mesoventral plate (compare Fig. 8f with Figs 7d and 13a) and yellow coloration of lateral part of elytra expanding to humeral area at elytral base, and from C. sklodowskae sp. n. by the bare median portion of mesoventrite not reaching anteriorly, bulged projection of the prosternum, metatibia slightly bent outwards, anterior margin of mentum not emarginated, and females without a triangularly bulging projection at apex of the fifth ventrite.
Distribution. The species group is endemic to Hispaniola and seems widespread on the island. No records are known from Haiti, likely due to collecting bias.  Diagnosis. Externally identical with other members of the Cercyon gimmeli species group, it may be only distinguished from them by the morphology of the aedeagus ( Fig. 5a-d): parameres longer than the phallobase; median lobe without spines, narrowly parallel-sided, with rounded apex.
Description. Body. (Fig. 1a-c) 2.8-3.5 mm long (length of holotype: 3.25 mm); long oval, 1.8-1.9× as long as wide, widest at basal fourth of elytra; moderately convex, 3.2× as long as high, (height of holotype: 1.05 mm). Coloration. Dorsal surface of head black, clypeus with widely yellowish anterolateral margins. Antennae and ventral surface of head, including mouthparts, brown, antennal club dark-brown. Pronotum black, with a wide, rather sharply defined creamy-white area along lateral margins, broader at anterior half. Prosternum and hypomeron brown, gradually turning black in posterior half. Elytra dark brown to black, with large, pale, rather sharply defined apical spot covering posterior quarter of elytral interval 1, and gradually larger portion on subsequent intervals up to posterior three-quarters of interval 9; two lateralmost intervals completely pale; apical area slightly darker (yellowish brown) posteriorly, with bright yellowish stripe or spots at least along its anterior border; basal portion of elytra with a pair of pale elongated dots at sides of scutellar shield. Ventral surface of mesothorax blackish to pitchy black. Metepisternum brown. Metaventrite brown with dusk anteromedial part. Abdomen brown, ventrites sometimes with dusky marks on anterior margin. Legs yellow to brown ventrally, dorsally with black markings on femora.
Head. Clypeus with rather sparse and shallow punctation consisting of crescentshaped setiferous punctures intermixed with denser, smaller and rather transverse nonsetiferous punctures; interstices without microsculpture. Anterior margin of clypeus with a narrow bead. Frontoclypeal suture conspicuous as a zone without punctuation, vanished in middle. Frons with punctation similar to that on clypeus, punctures of same shape all over, slightly sparser on sides; interstices without microsculpture. Eyes rather small; interocular distance about 6× the width of one eye in dorsal view. Labrum membranous, nearly completely concealed under clypeus, only with narrowly exposed sinuate anterior margin. Mentum (Fig. 8a) subtrapezoid, widest at posterior fourth, about 2.1× wider than long, 1.3× wider at widest part than at anterior margin, concave in anterior half, with a shallow transverse impression anteromesally; surface glabrous, punctures rather small and shallow, almost vanishing anteromessally, interstices without microsculpture. Antenna with 9 antennomeres, scapus ca. 1.7× as long antennomeres 2-6 combined; antennal club moderately elongate, about twice as long as wide, about as 1.1× as long as scapus; antennomere 9 acuminate at apex.
Prothorax. Pronotum transverse, widest at base 2.1-2.2× wider than long; 1.8× wider at base than between anterior angles, 1.8× wider than head including eyes, as convex as elytra in lateral view. Punctation moderately dense and shallow, consisting of crescent-shaped setiferous punctures intermixed with denser, smaller and rather transverse non-setiferous punctures; punctures slightly feebler on sides. Prosternum (Fig. 8b) strongly tectiform medially, medial ridge thickened in anterior half, forming a large rounded knob in lateral view (Fig. 8c). Antennal grooves distinct, with lateral margin curved, slightly feebler anteriorly.
Pterothorax. Scutellar shield 1.1× as long as wide, sparsely punctured. Elytra widest at anterior fifth, 2.55-2.85× as long as pronotum, 1.25-1.35× as wide as pronotum; surface glabrous ( Fig. 8d), with 10 series of punctures; series 6, 8 and 9 not reaching elytral base, serial punctures getting slightly larger laterally; intervals moderately convex; punctation of interval 1 and odd intervals composed of crescent-shaped setiferous punctures intermixed with denser, smaller and rather transverse non-setiferous punctures; even intervals with non-setiferous punctures only; all interstices without microsculpture. Humeral bulge indistinct. Mesoventral plate ( Fig. 8f ) narrowly elongate, ca. 5.7× as long as wide, widest at midlength, gradually and symmetrically narrowing posteriad and anteriad to pointed apices, posterior tip slightly overlapping over anterior portion of metaventrite; surface with few sparsely arranged coarse punctures. Metaventrite with narrow median raised pentagonal area (Fig. 8g), 1.1× as long as wide at widest portion, glabrous, weakly and sparsely punctuate, punctures with fine setae at least along margins of elevation, with bare area not reaching anterior margin; femoral lines absent; lateral parts of metaventrite densely covered by short pubescence.
Legs. Femora with sparse rather shallow punctures ventrally, interstices with weak microsculpture at bases, consisting of longitudinal lines; tibial grooves distinct. Tibiae with rather large lateral spines. Metatibiae moderately narrow and elongate, slightly bent outwards, 0.3-0.4× as long as elytra, 5.3× as long as wide. Metatarsus long, 0.9× as long as metatiba, with few short but rather stout setae ventrally.
Abdomen with five ventrites, first abdominal ventrite about as long as second and third ventrites combined, with distinct median longitudinal carina ( Fig. 8h) narrowing posteriad, not projecting posteriorly in both sexes; fifth ventrite ( Fig. 8i) with acuminate and very weakly bulged apex in both sexes.

Variability.
In some specimens the pale spots at sides of the scutellar shield are longer, almost reaching the second fourth of elytral length.
Etymology. We are pleased to dedicate this species to Matthew L. Gimmel (Santa Barbara Museum of Natural History), who participated in the expedition to the Dominican Republic and collected part of the type series of this species.
Biology. All specimens were collected in in broad-leaf tropical forests and coffee plantations and pastures, mainly on cow and horse dung, but also on human dung, rat carrion, at black-light or at day by beating. Diagnosis. Externally identical with other members of the Cercyon gimmeli species group, it may be only distinguished from them by the morphology of the aedeagus ( Fig. 5i-l): parameres as long as phallobase; median lobe moderately wide basally, narrowing apicad, with spines in apical fifth, apex finely truncate.
Conforming to the description of C. gimmeli, with the following differences: Pterothorax. Punctation of even intervals consisting of small non-setiferous punctures, but here and there with infrequent crescent-shaped larger setiferous punctures; only lateralmost elytral interval completely pale.
Etymology. The species name is derived from Latin words armatus (armed) and penis (penis), in reference to the diagnostic character of this species, i.e. the apex of the median lobe armed by small spines.
Biology. Specimens were collected in cow dung in a cloud forest.
Cercyon taino sp. n. Diagnosis. Externally identical with other members of the Cercyon gimmeli species group, it may be only distinguished from them by the morphology of the aedeagus ( Fig. 5e-g): parameres shorter than phallobase; median lobe without spines, narrowly parallel-sided, pointed at apex.
Conforming with description of C. gimmeli, with the following differences: Pterothorax. Punctation of even intervals consisting of small non-setiferous punctures, but here and there with infrequent crescent-shaped larger setiferous punctures; only lateralmost elytral interval completely pale.
Etymology. The new species is named after the indigenous Taíno people inhabiting the Greater Antilles including Hispaniola before and at the time of the arrival of Europeans.
Distribution. Dominican Republic (Samaná, La Vega, Independencia) (Fig. 15b). Biology. Examined specimens and the associated larvae (see below) were collected from leaf litter of montane forests and from cow dung. Diagnosis. Cercyon sklodowskae sp. n. can be easily differentiated from other Greater-Antilles Cercyon species by the following combination of characters: body size 3.1-3.5 mm; dorsal surface of head black with yellowish anterolateral margins of clypeus; pronotum black with sharply defined yellowish areas at lateral margins ( first abdominal ventrite without spiniform process in both sexes (Fig. 10h); apex of fifth abdominal ventrite with a triangular projection in females (Fig. 10i); aedeagus with very short parameres (Fig. 5m), median lobe ( Fig. 5o) covered with spines in apical third.
C. sklodowskae may be confused with C. praetextatus (Say) and Cercyon floridanus Horn and the members of C. gimmeli species group. It can be distinguished from C. praetextatus and C. floridanus by the head with widely yellowish clypeal margin and yellow coloration of elytra expanded basally (clypeus black and basal part of elytra only narrowly yellow in C. praetextatus and C. floridanus) and by much narrower mesoventral plate (5.8× as long as wide in C. sklodowskae, 1.9× as long as wide in C. floridanus and 3.3× in C. praetextatus). It differs from members of C. gimmeli group by the mesoventral plate reaching anterior part of metaventrite (not reaching anterior margin in C. gimmeli group), only a small rounded process of median prosternal ridge (large rounded knob in C. gimmeli group), straight metatibia (slightly curved outside in C. gimmeli group), and last abdominal ventrite in females forming a triangular projection (without projection in C. gimmeli group). It differs from all these species by the morphology of male genitalia; by the apically spinose median lobe it resembles C. armatipenis, but differs from it by parameres much shorter than phallobase.
Description. Body. (Fig. 2a-c) 3.10-3.45 mm long (length of holotype: 3.29 mm); long oval, 1.8-1.9× as long as wide, widest at basal fourth of elytra; moderately convex, 2.8-3.0× as long as high, (height of holotype: 1.1 mm). Coloration. Dorsal surface of head blackish to pitchy black, clypeus with wide rather sharply defined yellowish area along anterolateral margins, slightly broader at sides. Ventral surface of head dark brown, almost black on sides. Antennae, mentum and mouthparts dark brown. Pronotum blackish to pitchy black, with narrowly brownish lateral margins, broader at anterolateral corners (Fig. 2c). Prosternum and hypomeron black, with darker anterolateral margins. Elytron (Fig. 2a) black, with large, pale, rather sharply defined apical spot covering posterior quarter of elytral interval 1 and gradually larger portion on subsequent intervals up to posterior three-quarters on interval 9, lateralmost interval completely yellowish to dark brown; apical spot slightly darker (yellowish-brown) posteriorly, with lighter brown spots at least along its anterior border. Ventral surface of mesothorax (Fig. 2b) blackish to pitchy black. Metepisternum dark brown. Metaventrite black with darker anteromedial part and anterior margins. Abdomen black, posteromedial margins and anterolateral corners of ventrites darker. Legs dark brown.
Head. Clypeus with moderately dense and shallow punctation consisting of crescent-shaped punctures intermixed with denser, slightly smaller and rather transverse punctures; interstices without microsculpture. Anterior margin of clypeus with a narrow bead. Frontoclypeal suture conspicuous as a zone without punctation, vanishing mesally. Frons with punctation similar to that on clypeus, punctures sparser on sides; interstices without microsculpture. Eyes rather small; interocular distance about 6× the width of one eye in dorsal view. Labrum membranous, nearly completely concealed under clypeus, only with narrowly exposed sinuate anterior margin. Mentum (Fig. 10a) subtrapezoid, widest at posterior fourth, about 2.1× wider than long, 1.4× wider at widest part than at anterior margin, concave in anterior half, strongly emarginated anteromesally; surface glabrous, punctures rather small, shallow and sparse, almost vanishing anteromesally, interstices without microsculpture. Antenna with 9 antennomeres, scapus ca. 1.9× as long antennomeres 2-6 combined; antennal club moderately elongate, about twice as long as wide, about as 1.2× as long as scapus; antennomere 9 acuminate at apex.
Pterothorax. Scutellar shield 1.25× as long as wide, sparsely punctured. Elytra widest at anterior fifth, 2.7-3.0× as long as pronotum, 1.2× as wide as pronotum, surface ( Fig. 10d) glabrous, with 10 series of punctures; series 6, 8 and 9 not reaching elytral base, serial punctures of same size in all series; intervals moderately convex; interval punctation composed by crescent-shaped punctures intermixed with denser, slightly smaller and rather transverse punctures in all intervals. Humeral bulge indistinct. Mesoventral plate (Fig. 10f ) narrowly elongate, ca. 5.8× as long as wide, widest in anterior two-fifths, more strongly narrowing towards anterior apex which is pointed, posterior tip rounded, slightly overlapping over anterior portion of metaventrite; surface with a few sparse coarse punctures. Metaventrite ( Fig. 10g) with narrow raised pentagonal area, 1.2× longer than wide, glabrous, weakly and sparsely punctuate, punctures with fine setae at least along margins of the elevation; bare elevated area reaching anterior margin of metaventrite; punctures absent at two slightly elongate areas in the center; femoral lines absent; lateral parts of metaventrite densely covered by short pubescence.
Legs. Femora with sparse rather shallow punctures ventrally, interstices with weak microsculpture consisting of longitudinal lines; tibial grooves distinct. Tibiae with rather small lateral spines. Metatibiae moderately narrow and elongate, straight, 0.3-0.4× as long as elytra, 5.3× as long as wide. Metatarsus long, 0.9× as long as metatibia, with short rather stout setae ventrally.
Abdomen. With five ventrites, first abdominal ventrite (Fig. 10h) about as long as the second and third ventrites combined, with distinct median longitudinal carina narrowing posteriad, not projecting posteriorly in both sexes; fifth ventrite with acuminate apex, weakly bulged in males and with a triangularly bulged apical projection in females (Fig. 10i).
Etymology. We dedicate this species to the eminent physicist and chemist Marie Skłodowska-Curie, on whose honor the Marie Skłodowska-Curie actions program of the European Union, funding this research, is named.
Biology. The specimens were collected on dung and using dung and carrion-baited traps in cloud forests.
Cercyon floridanus is part of the C. tristis group according to Smetana (1978) It resembles members of the C. gimmeli species group, C. sklodowskae sp. n. and C. praetextatus. Besides of the features of the aedeagus (Fig. 7a-c), it can be easily distinguished from them by the distinctly by the smallersize (2.35-2.70 mm), wider mesoventral plate (1.9× as long as wide in C. floridanus, 3.3-5.8× as long as wide in the other species). Besides that, females of C. floridanus lack the triangular projection on the apex of the fifth abdominal ventrite (present in C. sklodowskae), has a very small process of mid-prosternal ridge (large in C. gimmeli species group), and almost straight metatibia (curved in C. gimmeli species group).
Distribution. Cercyon floridanus is distributed in the southeastern USA, mainly in Florida, but rare records are also known from Georgia, Louisiana and Mississippi (Smetana 1978). In the Greater Antilles it is only known from Cayman Islands, from where it was first reported by Thomas et al. (2013) under the name "C. floridanuus Smetana" (Fig. 16a).
Diagnosis. Body size 2.7-4.1 mm; dorsal surface of head (Fig. 2g) black, with a pair of small reddish-brown spots on vertex, sometimes fused to one spot; pronotum black with sharply defined yellowish to reddish areas at anterolateral corners, some-times extending to complete lateral margins; elytra black, with large sharply-defined yellowish to reddish-yellow lateroapical area reaching about apical fourth, laterally reaching elytral base in lateralmost interval, yellow spot not extended to humeral area basally; medial ridge of prosternum anteriorly forming a small rounded to slightly pointed process; mesoventral plate ( Fig. 13a) wide, ca. 3.3× as long as wide; metaventrite (Fig. 13b) without femoral lines, with narrow raised pentagonal area (ca. as long as wide); first abdominal ventrite without spiniform process in both sexes; apex of fifth ventrite without triangularly bulged projection at apex in both sexes; aedeagus (Fig. 6a-c) with parameres almost twice as long as phallobase, sinuately widened and bearing long setae at apex; median lobe widest at midlegth, narrowing to pointed apex, without spines. For complete description see Smetana (1978).
This species was assigned to the C. marinus group according to Smetana (1978). By the coloration of pronotum and elytra (Fig. 2g, i), C. praetextatus may be confused with members of the C. gimmeli species group and with C. sklodowskae sp. n. Besides of the features of the aedeagus (Fig. 6a-c), it can be easily distinguished from them by the distinctly wider mesoventral plate (3.3× as long as wide in C. praetextatus, 5.7-5.8× as long as wide in the other species) and the yellow stripe along lateral margin of elytra not expanding basally. Besides of that, females of C. praetextatus lack the triangular projection on the apex of the fifth abdominal ventrite (present in C. sklodowskae), has a very small process of mid-prosternal ridge (large in C. gimmeli species group), and almost straight metatibia (curved in C. gimmeli species group).
Distribution. Cercyon praetextatus is widely distributed in North America (southern Canada, USA, Mexico; Smetana 1978;Ryndevich 2004) and reaches to Central America (Guatemala, Costa Rica; Smetana 1978) and to the Caribbean (Cayman Islands, Cuba, Dominican Republic, Jamaica, Smetana 1978, Spangler 1981; it has also been introduced to Argentina (Fikáček 2009). We report it here from Dominican Republic (La Vega Province) and the Cayman Islands for the first time (Fig. 15c).
Biology. This species seems to prefer wet environments, living primarily on many kind of organic debris, like decomposing plant remnants, carrion and dung (Smetana 1978). In Cuba and the Dominican Republic this species has been attracted to light.   Diagnosis. Body size 3.4-4.1 mm; dorsal surface of head black with yellowish anterolateral margins of clypeus (Fig. 3a); pronotum homogeneously light brown, elytra greyish-brown; medial ridge of prosternum anteriorly with a small rounded process (Fig. 11c); mesoventral plate narrow, ca. 5.9× as long as wide; metaventrite (Fig. 11f ) without femoral lines; raised pentagonal area of metaventrite moderately wide, 0.9× as long as wide; first abdominal ventrite with an spiniform process in females (Fig. 11h), without process in males; apex of fifth abdominal ventrite without apical triangular projection in both sexes (Fig. 11i); aedeagus with parameres about as long as phallobase (Fig. 6e), median lobe narrowly parallel-sided, acute at apex, without spines.
Cercyon spiniventris somewhat resembles C. nigriceps by the dorsal coloration pattern (predominantly black head and rather homogeneously brown pronotum and elytra); it can be easily distinguished from C. nigriceps by much larger body size (3.4-4.1 mm in C. spiniventris, 1.0-2.1 mm in C. nigriceps) and by the lack of femoral lines on the metaventrite (present in C. nigriceps). Cercyon spiniventris is unique among Caribbean Cercyon species by a presence of a long spiniform process in the first abdominal ventrite of females.
Description. Body (Fig. 3a-c). 3.4-4.0 mm long (length of holotype: 3.5 mm); moderately short-oval, 1.8-1.9× as long as wide, widest at basal fourth of elytra; moderately convex, 2.9-3.0× as long as high (height of holotype: 1.15 mm). Coloration. Dorsal surface of head blackish to pitchy black, clypeus with wide rather sharply defined yellowish area along anterolateral margins, broader at sides. Antennae and ventral surface of head black, mentum with posterior half yellowish brown, mouthparts and antenna yellowish brown, antennal club dark-brown. Pronotum light brown. Prosternum yellowish-brown with posterior half black, hypomeron brown with large black marks on posterior third, and close to the yellowish-brown lateral margins. Elytra dark greyish-brown, with lateral and anterior margins, apex and epipleura slightly paler. Ventral surface of mesothorax blackish to pitch-black, with procoxal rests and mesoventral plate brown. Metepisternum black. Metaventrite black with paler raised anteromedial part. Abdomen black, posteromedial margins and anterolateral corners of ventrites brownish. Legs brown, femora dorsally black.
Head. Clypeus with dense and moderately deep punctation consisting of crescentshaped setiferous punctures intermixed with denser, smaller and rather transverse nonsetiferous punctures; interstices without microsculpture. Anterior margin of clypeus with a narrow bead. Frontoclypeal suture conspicuous as a zone without punctuation, vanished mesally. Frons with punctation similar to that on clypeus, punctures of same shape all over; interstices without microsculpture. Eyes rather small; interocular distance about 5.4× the width of one eye in dorsal view. Labrum membranous, nearly completely concealed under clypeus, only with narrowly exposed sinuate anterior margin. Mentum (Fig. 11a) subtrapezoid, widest at posterior fourth, about 2× wider than long, 1.5× wider at widest part than at anterior margin, weakly concave in anterior half; surface glabrous, punctures large and deep, becoming coarser anteromesally, interstices on anterior half with transverse depressions near each puncture. Antenna with 9 antennomeres, scapus ca. 1.8× as long as antennomeres 2-6 combined; antennal club moderately elongate, about twice as long as wide, about as 1.2× as long as scapus; antennomere 9 acuminate at apex.
Pterothorax. Scutellar shield about as long as wide, moderately densely punctured. Elytra widest at anterior fifth, 2.7-2.9× as long as pronotum, 1.1-1.2× as wide as pronotum, surface (Fig. 10d) glabrous, with 10 series of punctures; series 6, 8 and 9 not reaching elytral base, serial punctures of same size in all series; intervals moderately convex; interval punctation composed of crescent-shaped setiferous punctures intermixed with denser, smaller and rather tranverse non-setiferous punctures; setiferous punctures present on all intervals; interstices without microsculpture. Humeral bulge indistinct. Mesoventral plate (Fig. 11f ) narrowly elongate, ca. 5.9× as long as wide, widest at midlength, gradually and symmetrically narrowing to pointed apices, posterior tip slightly overlapping over anterior part of metaventrite; surface with coarse punctures. Metaventrite (Fig.  11g) without femoral lines, raised pentagonal area wide, 0.8× as long as wide at widest portion, glabrous, rather weakly and sparsely punctate, punctures with fine setae at least along margins of elevation, punctures absent at two slightly elongate areas in the center, bare area not reaching anterior margin of metaventrite mesally; lateral parts of metaventrite densely covered by short pubescence.
Abdomen with five ventrites, first abdominal ventrite longer than second and third ventrites combined, with long setae in medial third, median longitudinal carina present, slightly narrowing posteriad, not projecting posteriorly in males, projecting posteriad as a short spine in females (Fig. 11h); ventrite 5 with acuminate apex in both sexes.
Etymology. The name of this species is derived from Latin words spina (spine) and venter (underside), in reference to the spine-like process on the first abdominal ventrite of females.
This species was assigned to C. nigriceps group (= C. atricapillus group) by Smetana (1978). Cercyon nigriceps can be distinguished from other species in the region by its small size and the presence of complete femoral lines on the metaventrite. It may be confused with representatives of the genus Oosternum by the small body size and coloration, but differs from them by presence of femoral lines (absent in Oosternum), absence of anterolateral ridge on mesoventrite (present in all Oosternum) and by very narrow mesoventral plate (1.7-2.8× as long as wide in Oosternum, see Deler- Hernández et al. 2014).
Distribution. This is an adventive species currently distributed in all zoogeographical regions. In Greater Antilles widespread in all islands: Cayman Islands, Cuba (Artemisa, Cienfuegos, Guantánamo, Holguín, Matanzas, Santiago de Cuba; Gundlach 1891), Dominican Republic (La Altagracias, La Vega, Monte Cristi, Samaná, San Pedro de Macoris; this paper), Haiti (Artibonite, this paper), Jamaica (Trelawny; Fikáček 2009) and Puerto Rico (Naguabo, Arecibo, Cabo Rojo). It is also widespread in the Lesser Antilles (Antigua, Grenada, Saint Lucia, Saint Vincent and the Grenadines; this paper) (Fig. 16b). Based on the record by de la Sagra (1857), the species was introduced to the Greater Antilles no later than the first half of the 19 th century.
Biology. A terrestrial species collected in cow and horse dung and in decaying plant matter (e.g., compost piles). It is also frequently collected at light.
Cercyon quisquilius was assigned to C. unipunctatus group according to Smetana (1978). This species can be only confused with C. nigriceps in Greater Antilles. It may be distingushed from it by the coloration of the pronotum (blackish with diffuse yellowish areas on lateral margins in C. quisquilius, almost homogeneously piceous to reddish brown and similar to elytral coloration in C. nigriceps), larger body size (2.4-3.2 mm in C. quisquilius, 1.0-2.1 mm in C. nigriceps), and by metaventrite without femoral lines and with wide raised median part (with femoral lines and narrower median part in C. nigriceps).
Distribution. Cercyon quisquilius is a species native to the Palearctic Region, but currently introduced to the Nearctic, Neotropical and Australian Regions (Smetana 1978;Hansen 1999;Fikáček 2009). We are providing the first precise records of this species from the Caribbean based of specimens from Cuba (Holguín province) (Fig. 15c).         Published records (as C. variegatus). JAMAICA: without precise locality (Smetana 1978). PUERTO RICO: without precise locality (Smetana 1978). DOMINICA: without precise locality (Leng and Mutchler 1917;Peck 2006).

Cercyon insularis Chevrolat, 1863
Diagnosis. Body size 2.4-3.4 mm; dorsal surface of head (Fig. 4a) black with a pair of small pale spots on vertex (sometimes fused in one central spot), pronotum yellowish to dark reddish-brown with a large blackish central spot and two small round blackish spots at sides (sometimes obscured); elytra yellowish with black humeral spot, in dark specimens whole elytral base and suture darkened; medial ridge of prosternum not projected ventrally (Fig. 12c); mesoventral plate narrow, 5.8× as long as wide (Fig. 12f ); metaventrite (Fig. 12g) without femoral lines, with raised pentagonal area as long as wide; first abdominal ventrite without spine-like process in both sexes (Fig. 12h); apex of fifth abdominal ventrite (Fig. 12i) without apical projection in both sexes; aedeagus narrow, parameres 0.7× as long as phallobase (Fig. 4f ), rounded at apex; median lobe ( Fig. 4g) subparallel throughout except for acuminate apex, without subapical spines.
Redescription. Body. (Fig. 4a-d) 2.4-3.4 mm long (length of holotype: 2.8 mm); moderately elongate oval, 1.7-1.8× as long as wide, widest at basal fifth of elytra; moderately convex, 2.6-2.8× as long as high (height of holotype: 1.0 mm). Coloration. Dorsal surface of head black with a pair of small rufotestaceous spots on vertex. Antennal scape and flagellum and ventral surface of head including mouthparts light-brown, antennal club and mentum dark brown. Pronotum yellowish to dark reddish-brown, with a large blackish central spot and two small round blackish spots at its sides, sometimes connected with central spot. Prosternum yellowish to light brown, hypomeron slightly darkened. Elytra with elongate blackish spot posterior to humeri, elytral base and suture darkened, elytral epipleura uniformly pale. Ventral surface of mesothorax blackish. Metepisternum brown. Metaventrite blackish, darker at medial elevation. Abdomen yellowish to reddish-brown. Legs yellowish to light brown.
Head. Clypeus with moderately dense and shallow punctation consisting of small transverse punctures; interstices without microsculpture. Anterior margin of clypeus with narrow bead. Frontoclypeal suture conspicuous as a zone without punctuation, vanished mesally. Frons with punctation similar to that on clypeus, punctures sparser on sides; interstices without microsculpture. Eyes rather small, interocular distance about 6× the width of one eye in dorsal view. Labrum membranous, nearly completely concealed under clypeus, only with narrowly exposed sinuate anterior margin. Mentum (Fig. 12a) subtrapezoid, widest at posterior fourth, about 2× wider than long, 1.5× wider at widest part than at anterior margin, strongly concave in anterior half, anterior margin not emarginate; surface almost glabrous, punctures small, shallow and sparse, almost vanishing anteromesally, interstices without microsculpture. Antenna with 9 antennomeres, scapus ca. 1.8× as long antennomeres 2-6 combined; antennal club moderately elongate, about twice as long as wide, as long as scapus; antennomere 9 acuminate at apex.
Prothorax. Pronotum transverse, widest at base 2.1-2.2× wider than long; 1.7-1.8× wider at base than between front angles, 1.8× wider than head including eyes, as convex as pronotum in lateral view. Punctation rather dense and moderately deep, consisting of crescent-shaped punctures intermixed with denser, slightly smaller and rather transverse punctures; punctures slightly feebler on sides. Prosternum (Fig. 12b) strongly tectiform medially, median ridge ( Fig. 12c) with the same width throughout, anterior apex not projecting ventrally. Antennal grooves distinct, with lateral margin curved.
Legs. Femora with sparse shallow punctures ventrally, interstices with weak microsculpture consisting of longitudinal lines; tibial grooves distinct. Tibiae with rather small lateral spines. Metatibiae moderately broad and long, straight, 0.33× as long as elytra, 5× as long as wide. Metatarsus long, 0.86-0.89× as long as metatibia, with just a few short rather stout setae ventrally.
Abdomen with five ventrites, first abdominal ventrite (Fig. 12h) about as long as the second and third ventrites together, with distinct median longitudinal carina narrowing posteriad, not projecting posteriorly in both sexes; fifth ventrite with acuminate apex and weakly bulged in both sexes (Fig. 12i).
Variability. The general dorsal coloration of the pronotum and elytra varies from yellow to dark reddish-brown. In dark specimens, lateral pronotal spots join the large central spot, and the whole anterior part of elytra and the elytral suture are distinctly darkened, with pale areas maintained in humeral area and at sides of scutellar shield. In pale specimens, the lateral pronotal spots are rather small and sometimes very vague and indistinct, and the elytra are completely yellow except base, sutural interval and the posthumeral dark spots.
Distribution. Cercyon insularis seems to be widely distributed across Greater and Lesser Antilles, here we are recording it from Cuba, Dominican Republic, Puerto Rico, Grenada, Saint Lucia and Dominica. It seems that all records of C. variegatus from the Caribbean (Jamaica, Puerto Rico : Smetana 1978;Dominica: Peck 2006) actually concern C. insularis, as we failed to find the true C. variegatus in the material examined. For that reason we consider C. insularis to occur in Jamaica, although we did not examine any specimens from Jamaica ourselves.
Bionomics. Most of the specimens were collected in cow and horse dung on pastures, in coffee plantations and in tropical forests; few were collected using flight intercept traps.
Discussion. Chevrolat (1863) described C. insularis based on a single specimen from Cuba collected by D. F. Poëy and deposited in Chevrolat's collection. On our request to loan this specimen, we received a single specimen standing under the name C. insularis in the Chevrolat collection, corresponding well with the original description and marked as a type. In contrast to the data mentioned by Chevrolat (1863), the specimen also bears a label indicating Habana as the place of its origin. Since there is no reason to doubt the type identity of this specimen, we correct the type locality of C. insularis to Habana, in agreement with the label data of the holotype.
Cercyon insularis was only briefly mentioned once by Gundlach (1891) and its type was not reexamined, therefore its identity remained unclear. Our inspection of the type revealed it corresponds by coloration with what was recorded from the Caribbean as Cercyon variegatus Sharp, 1882, by Smetana (1978), Hansen (1999) and Peck (2006). In order to determine the identity of the species present in the Caribbean we studied the lectotype of C. variegatus (Fig. 4j-o, deposited in BMNH) and compared it to the type of C. insularis and additional recently collected material from Cuba. Based on this comparison, it became clear that Cuban specimens are not conspecific with C. variegatus, but belong to a different species indistinguishable from it by external morphology: all dissected Cuban specimens were conspecific, differed from C. variegatus by genital morphology, and no other species of the same external coloration was found. We hence consider the Cuban specimens conspecific with the type specimen of C. insularis, even though it cannot be dissected because of its poor condition. Both median lobe (Fig. 4g) as well as phallobase and parameres (Fig. 4f) are narrower in C. insularis than in C. variegatus. The apices of parameres are rounded in C. insularis, while they are more acuminate in C. variegatus (Fig.  4l). Moreover, the apex of the median lobe of C. variegatus has a small flank on each side (Fig. 4n) (Full set of pictures of the lectotype of C. variegatus in www.flickr.com/photos/142655814@N07/albums/72157676248390724).
Cercyon insularis and C. variegatus belong to a species complex corresponding to the C. variegatus group of Smetana (1978), distributed from the southern USA to Argentina; the species within this complex can be only distinguished by the morphology of the male genitalia (Arriaga-Varela and Fikáček, pers. observation). Only two species of this species complex have been formally described (C. variegatus and C. insularis) and the group requires a detailed revision. The species recorded from Suriname as "Cercyon rishwani" by Makhan (2004) also belongs to this species complex based on color pattern of the pronotum and the general shape of the aedeagus, but a more detailed comparison with C. insularis and C. variegatus is impossible based on the description and illustrations provided. "Cercyon rishwani Makhan, 2004" is moreover considered a nomen nudum (see Short and Hebauer, 2006 for details).

Larval morphology
Cercyon taino sp. n. Larval diagnosis. Head capsule (Fig. 14e) longer than wide; cuticle with polygonal microsculpture; head capsule with two "lenses" (anteriorly and posterior of the eye spot) on each side, lateral part of head capsule without apparent group of setae ca. at midlength; clypeolabrum uniformly arcuate at the right side from the setiferous emargination. Metanotum (Fig. 14a) with wide and strongly sclerotized transverse tergite. Legs (Fig. 14d) reduced into two-segmented vestiges. Membranous parts of thorax and abdomen (Fig. 14a-c) covered by long blackish cuticular projections. Abdominal segments acutely lobate laterally, abdominal segments 1-7 each with three transverse rows of low tubercles. Tergite on 8th abdominal segment (Fig. 14f ) ca. as long as wide, deeply sinuate on anterior margin, with three slightly acute lobes on posterior margin.  Larval diagnosis. Head capsule (Fig. 14k) ca. as long as wide; cuticle smooth, without distinct miscrosculpture; head capsule with two "lenses" (anteriorly and posterior of the eye spot) on each side, lateral part of head capsule with apparent group of setae (PA12-14 sensu Fikáček et al. 2008) ca. at midlength; clypeolabrum angulate at the right side from the setiferous emargination. Metanotum (Fig. 14g) with very narrow and weakly sclerotized transverse tergite. Legs (Fig. 14g) reduced into one-segmented setiferous tubercle. Membranous parts of thorax and abdomen covered by extremely short and dense whitish microtrichia. Abdominal segments (Fig. 14g-i) without lateral lobes, smooth (i.e. without transverse rows of tubercles) dorsally. Tergite on 8th abdominal segment (Fig. 14l) wider than long, shallowly sinuate on anterior margin, weakly sinuate on posterior margin.

Analysis of molecular data
Partial COI sequences of the 19 Cercyon specimens sampled resulted in a 610 bp alignment. JModelTest (Darriba et al. 2012) determined the GTR+I+G model as best nucleotide substitution model. The resulting maximum likelihood tree revealed 7 clades corresponding to the species as defined by morphological characters (Fig. 17). The statistical support for all species clades containing multiple specimens was high (bootstrap 100%), whereas the backbone of the phylogeny was poorly supported (bootstrap 53-85%), corresponding to the fact that we used a single marker with high substitution rate with limited information content for interspecific phylogeny, especially when introduced (and hence likely not closely related) species were included in the analysis. However, we recovered the C. gimmeli species complex as a well-supported monophyletic group, containing three well separated lineages (corresponding to the species as delimited by genital morphology) with mean interspecific distances 9-10 %. Sequenced females of the C. gimmeli species complex, morphologically not identifiable to species, were all unambiguously associated with male specimens and included as paratypes.
Cercyon insularis, C. spiniventris and the introduced species were also revealed as well separated lineages in our analysis. The intraspecific genetic distances were low in all species for which multiple specimens were included, ranging between 0.0 to 1.4 %. Larval specimens were unambiguously assigned to co-occuring adults in both cases (larva MF1261.L to C. taino, larva MF1731.L to C. insularis). The only sequenced specimen of C. nigriceps from Puerto Rico is genetically very similar to that of Finland (genetic distance 0.6 %) (See supplementary material 2).

Discussion
Faunal composition of Cercyon in the Greater Antilles. Our revision raises the number of Cercyon species from six to 10, and shows that the composition of the fauna largely differs from the original ideas: (1) five species, i.e. half of the fauna, are probably single-island endemics (four species in Hispaniola, one in Jamaica) and one additional species (C. insularis) seems to be a widespread Caribbean endemic not occurring in the mainland Americas; (2) only two species occurring in the Greater Antilles (C. praetextatus and C. floridanus) are native to the American continent, of which C. floridanus is moreover limited only to Cayman islands and does not occur in the four main islands of Greater Antilles; (3) two introduced Old World species (C. nigriceps and C. quisquilius) occur in the Greater Antilles, both of which are nowadays also widespread in the American continent (Smetana 1978;Fikáček 2009). The widespread continental Cercyon variegatus which was originally recorded from Jamaica and Puerto Rico by Smetana (1978) does not occur in the Caribbean Region at all, and is replaced there by morphologically very similar and likely closely related C. insularis.
The comparison of the original ideas about the Cercyon fauna and its real composition corresponds to the situation found in many other groups of minute arthropods, which were recently studied in the Greater Antilles. These studies frequently discover higher numbers of single-island endemics than expected, and reveal that some widespread continental species recorded from the Caribbean are in fact endemic species closely related but not identical to the continental ones (e.g., Dziki et al. 2015;Agnarsson et al. 2016).
The probable single-island endemics discovered during this study are distributed in Hispaniola (four species) and Jamaica (one species) only. No new species were discovered in Cuba and Puerto Rico, despite our collecting effort in both islands. Our field work in Puerto Rico was rather short and did not cover all mountain regions. Therefore, we cannot exclude additional discoveries in the island. On the other hand, our sampling effort was highest in Cuba, with intensive field work performed in 2010-2016. Hence we consider the discovery of a new endemic species in Cuba less likely. This puts in contrast Cuba, i.e. the largest Greater Antillean island, with no endemic species, with the smaller Hispaniola, hosting at least four single-island endemics. Moreover, the discovery of C. armatipenis sp. n. in a single locality in Sierra de Neiba at the Dominican-Haitian border indicates that additional species may be expected in this species complex in the western part of the island (i.e. Haiti) which was not sampled so far. In the same manner, there is a chance that the only species so far known exclusively from the Lesser Antilles, Cercyon cribratus Castelnau (1840), described from Guade-loupe island, could be present in the Greater Antilles. However, we were not able to find any specimen fitting its description in the examined material.
Both the extremely similar morphology and results of the analysis of the COI sequences imply that the C. gimmeli species complex forms a monophyletic clade endemic to Hispaniola. The fact that all species of the complex occur sympatrically and no clear geographic pattern can be observed in their ranges suggests that the radiation of this group in Hispaniola may be a result of subdivision of Hispaniola in smaller paleoislands during the Oligocene to Middle Miocene followed by range expansion when the paleoislands got interconnected more recently (Iturralde-Vinent and MacPhee 1999;Iturralde-Vinent 2006;Matos-Maravi et al. 2014). The group would be hence a good model for a further more detailed biogeographic study.
Novel morphological characters. Morphological studies of the Greater-Antillean Cercyon revealed some characters of adults relevant to species discrimination and identification, but not used before: the presence/absence and shape of the projection of the anterior part of the prosternal medial ridge, and the sexually dimorphic characters of abdominal ventrites found in C. spiniventris and C. sklodowskae. Females of C. spiniventris are characterized by a spine-like process on the first abdominal ventrite (absent in males), which has not been recorded in any other Cercyon species so far, but is present in females of the Australian megasternine genus Cercyodes Broun (Hansen 1990). Females of C. sklodowskae are characterized by modified shape of the fifth abdominal ventrite (compared to simple one in males). We have observed the variation of the shape of the fifth ventrite also in some other Cercyon species (without checking their sex). Hence the sexual dimophism in this character may be more widespread than expected.
Interesting discoveries were also made by a brief examination of the larvae of C. insularis and C. taino. Both larvae are surprisingly quite different from each other, differing especially in the head proportions, extent of leg reduction, shape of the tergite of 8 th abdominal segment, and surface vestiture membranous parts of thorax and abdomen. In all these characters, C. insularis is more similar to other Cercyon larvae described in the literature (C. quisquilius and C. praetextatus : Archangelsky 2016;C. melanocephalus and C. haemorrhoidalis: De Marzo 2000;C. unipunctatus, C. pygmaeus and C. lateralis: Schulte 1985). When examining the larval head of both C. insularis and C. taino, we found two circular areas of thickened transparent cuticle, one situated just in front of the ocular spot and another one just behind it (the areas are also visible as paler spots in lateral view of the head). We suppose that these areas of thickened cuticle may function as lenses. This character was never studied in sphaeridiine larvae and the only information about the ocular region available in the literature concerns the presence and shape of the pigmented "ocular spots": in larval Megasternini one spot is present, interpreted as an aggregation of all six stemmata or three anterior stemmata only (Hansen and Richardson 1998;Archangelsky 1999). Additional studies are needed to understand the function of this structure and its distribution in the Megasternini and Sphaeridiinae. One lens is present on each side of the head capsule of the larvae of C. praetextatus and the unidentified Japanese larvae of Cercyon (M. Archangelsky and Y. Minoshima, pers. comm. 2016), and two lenses (one before and one behind the pigmented spot) are present on each side of the head of larval Sphaeridium, i.e. the sister-group to the tribe Megasternini (M. Archangelsky, pers. comm.).
The novel characters mentioned above of both adults and larvae are useful for diagnostic purposes, but can also have phylogenetic signal which will help to corroborate the results of the ongoing phylogenetic study of the tribe Megasternini. The differences found between the larvae of C. insularis and C. taino and the differences in the number of lenses between different megasternine taxa show that larval morphology of the Megasternini is not that uniform as previously believed, and is in need of more studies.
Subgeneric assignment of the Greater Antilles Cercyon species. All species treated in this paper fall into the concept of Cercyon sensu stricto. However, we refrain from assigning them to any subgenus since the systematics of the genus Cercyon and allies is currently under study, and previous studies have shown that Cercyon in the current concept may be a polyphyletic assemblage of species (e.g. Short and Fikáček 2013). Newly discovered characters of adults and larvae discussed above also indicate that Cercyon is much more morphologically heterogeneous than expected, which corresponds to its supposed polyphyly.

Author contribution
ADH, MF and MS performed the field work; EAV and MF accumulated additional museum material; EAV performed the majority of morphological studies, prepared the first draft and photodocumentation; EAV and MS did the molecular work, analysis of the data and prepared the data for submissions to BOLD; VS, MF and EAV prepared the datasets, wrote and tested the scripts, and submitted the data to BOLD, GBIF and Flickr; all authors commented drafts of the paper at different stages and helped with completing the manuscript for submission.