Taxonomic review of New World Tachyina (Coleoptera, Carabidae): descriptions of new genera, subgenera, and species, with an updated key to the subtribe in the Americas

Abstract The classification of the carabid subtribe Tachyina (Trechitae: Bembidiini) is reviewed in light of newly discovered diversity from Central and South America. Described herein are three new genera (Tachyxysta gen. n., Stigmatachys gen. n., Nothoderis gen. n.), two new subgenera of Meotachys (Scolistichus subgen. n., Hylotachys subgen. n.), and two new subgenera of Elaphropus (Ammotachys subgen. n., Idiotachys subgen. n.). Two names previously synonymized under Polyderis (Polyderidius Jeannel, 1962) and Elaphropus (Nototachys Alluaud, 1930) are elevated to generic and subgeneric status, respectively. Eight new species are recognized: Tachyxysta howdenorum (type locality: México: Chiapas: El Aguacero, 680m); Elaphropus marchantarius (type locality: Brazil, Amazonas, Rio Solimões, Ilha de Marchantaria), Elaphropus acutifrons (type locality: Brazil: Pará, Santarém) and Elaphropus occidentalis (type locality: Perú: Loreto, Pithecia, 74°45'W 05°28'S); Stigmatachys uvea (type locality: Perú: Loreto: Campamento San Jacinto, 2°18.75'S, 75°51.77'W, 175–215m); and Meotachys riparius (type locality: Colombia: Amazonas: Leticia, 700 ft), Meotachys ballorum (type locality: Brazil: Amazonas, Rio Negro Cucui), and Meotachys rubrum (type locality: Perú: Madre de Dios: Rio Manu, Pakitza, 11°56°47'S 071°17°00'W, 356m). An updated key to the genera and subgenera of Tachyina occurring in the New World is provided, with accompanying illustrations.


Introduction
The cosmopolitan carabid subtribe Tachyina includes about 800 described species. In the Americas, tachyine diversity is greatest in the tropics, with species documented from a wide variety of habitats (riparian, hypogean, arboreal, corticolous, myrmecophilous, etc.). Detailed accounts of New World tachyine natural history are provided in previous publications by Erwin (1974bErwin ( , 1991 and Adis et al. (1986).
Among Bembidiini, tachyines are well-defined morphologically. All but a few tachyines have at least a trace of an elytral apical recurrent groove, which can vary in form ( Fig. 1C-F). The apicolaterally notched protibiae (visible in Fig. 2D-G, I) of all Tachyina s. str. easily distinguish them from their closest relatives, the Xystosomina, which possess simpler, truncate protibiae (Erwin 1994). The mentum of a tachyine beetle may either bear paired foveae (Fig. 1G) or lack these structures (Fig. 1H), and though major taxonomic groups of tachyines can be classified broadly according to this character (see Figure 5 in Ortuño and Arillo 2015), it is unlikely to be phylogenetically informative. The scope of this review is limited to the Tachyina of the New World, including brief diagnoses of all New World genera, as well as descriptions of new genera and new taxa that serve to clarify the boundaries and definitions of existing genera. Many additional species await description. The genus Meotachys Erwin, 1974 includes a small number of undescribed species (including the largest tachyine known from the New World) in addition to those representing the two new subgenera described below. This genus is of special interest due to its diversity, its potential key phylogenetic position, and the discovery of several unique external characters. Known species of Meotachys vary remarkably in size and form, though all share a distinctively shaped apical portion of the 8 th elytral interneur. Meotachys is unusually heterogeneous for a group of its size; alternatively, the species richness and diversity of this group may be much larger than that which is currently represented in collections. Distributed from México to central Brazil, Meotachys species are associated with silty river margins, understory bamboo thickets (Erwin 1991), and the seasonal white water (várzea) and black water (igapó) inundation forests that occur throughout the Amazon basin.
Among the "non-bifoveate' Tachyina (Ortuño and Arillo 2015), the speciose and morphologically diverse genus Elaphropus is defined by a lack of features diagnostic for other genera (e.g., Micratopus, Lymnastis, Anomotachys, Tachyta, etc.) rather than by a convincing set of synapomorphies. Despite the suspect monophyly of Elaphropus, previous authors have indicated with varying degrees of certainty that its relatively well-defined subgeneric level groups belong to a "phyletic line" (Sciaky and Vigna-Taglianti 2003). Assignment of several new species described below to Elaphropus is done so according to historical precedent and is somewhat tentative, as these taxa may represent separate genera pending further study. The development of a molecular phylogeny of the subtribe is in progress; with a focus on deep taxon sampling in Elaphropus (Tachyura) and allies, molecular data should help illuminate natural groups among this group's numerous and disparate species.

Material examined
Codes for the institutions where type material will be deposited appear in the text as follows:

AMNH
American Morphological methods: specimen preparation and imaging DNA voucher specimens representing some of the taxa described were available from a separate project. Males were dissected following DNA extraction. Genitalia were cleared in KOH and mounted in Euparal following the procedure described by Maddison (2014). Photo references for illustrations of genitalia were obtained using a JVC KY-F75U camera-equipped Leica DM5500 B compound microscope in bright field illumination. External structures were examined using a Leica M165 C dissecting microscope. Measurements were taken digitally using a camera-equipped Leica Z6 and the software Cartograph (Microvision). Measurements represent a range from the smallest to largest specimen examined. Abbreviations and definitions of measurements provided are listed below. Photomicrographs obtained with this system were compiled into stacked images using the photomontage software Zerene Stacker (Zerene Systems). Digital illustrations were prepared from reference photos using Adobe Creative Cloud software tools (Adobe Systems 2015).

Descriptive terms
Morphological terms generally follow the conventions established by Erwin (1974a). Elytral ombilicate (Eo) setae are named by position according to Erwin's (1974a) chaetotaxy system. Elytral discal (Ed) setae are simply counted and referred to in ascending order from base to apex, beginning with the scutellary seta (Ed1). Arrangement of humeral setal insertions is discussed in the key as either symmetric (with notation d(1,2) = d(3,4) indicating a distance between the first and second setae which is more or less equal to the distance between setae three and four), or asymmetric (with notation d(3,4) > d(1,2) and d(3,4) > d(2,3) indicating unequal spacing among humeral setae). Several commonly used terms are abbreviated in the key and text as follows:

i1
elytral interneur 1 (closest to suture) i8 elytral interneur 8 (closest to lateral margin) Ed elytral discal seta Eo elytral ombilicate seta ABL apparent body length (labrum to elytral apex of specimen in horizontal view) SBL standardized body length (labrum to posterior supraorbital seta + pronotum from base to apex at center line + base of scutellum to elytral apex) TW total width across widest point of both elytra ARG elytral apical recurrent groove Label data are listed verbatim, with label breaks denoted as follows: "label data" / "begin new line on label" // "begin second label".  5D); i8 curvy and deeply impressed in apical half, abruptly bent at Eo5-6 and around Eo7 (Fig. 4D)
Distribution. Known from várzea white water inundation forests of the upper to middle Amazon River drainage (Erwin 1984).
Distribution. Often abundant at lights, this speciose and underdescribed genus is known from southern North America to northern South America and the Caribbean (Erwin 1991, Erwin et al. 2002.
Diagnosis. Mentum without foveae; labrum bilobed, covering mandibles; head with two pairs of supraorbital setae; elytra slightly truncate; terminal abdominal ventrite of male with two long, straight setae, female with four long, straight setae; body densely to sparsely setose.
Distribution. This Old World genus is adventive in Hawaii and the Caribbean (Erwin et al. 2002).
Distribution. Known from sandy riparian habitats throughout the Amazon basin, from the eastern Andes of Ecuador and Perú to the Atlantic coast of South America (Erwin 1974;Kavanaugh 1999, 2007).
Distribution. Widely distributed from the boreal Nearctic to Central America and the Caribbean, associated with fallen logs (Erwin 1975 2I); antennae and legs lighter, rufotestaceous except for darker basal half of coxae; dorsally glabrous and without microsculpture except for labrum.
Distribution. The Mexican specimens were collected near or in El Ocote Preserve; the Honduran specimen was collected in an area near Comayagua National Park. Based on collection data from a limited number of specimens, T. howdenorum may be restricted to higher altitudes.
Derivation of name. Feminine. Derived from Tachys, the nominate genus of the subtribe Tachyina, and the Greek xustos (="smooth/polished"), in reference to this species' unmicrosculptured, glabrous dorsal surface and alluding to its general resemblance to some members of the subtribe Xystosomina, particularly those of the genus Erwiniana. Description. Size, form, color, head, prothorax, pterothorax, abdomen, genitalia, and distribution as in description of the genus.
Derivation of specific epithet. The patronym howdenorum honors Henry and Anne Howden, collectors of the holotype. The Howdens collected several examples included in the type series of T. howdenorum two decades apart in different locations.
Remarks. Despite its superficial resemblance to the genus Xystosomus, T. howdenorum possesses a combination of characters that support its placement among the Tachyina but discourage its membership in any previously described tachyine genus; T. howdenorum has an apicolaterally notched protibia and an apical recurrent groove reminiscent of Tachyta, but lacks the denticulate tarsal claws diagnostic for that genus (Erwin, 1975).

Subgenus
Head. Mentum without foveae. Prothorax. Basal section of pronotum ( Fig. 3F) triangular, rugose, with basal transverse impressions not well-defined; pronotum with dark, medial furrow that does not reach anterior margin; pronotal furrow with shallow basal excavation; convergent transverse impressions barely visible along anterior margin of pronotum; basal protarsomere of male with prominent medial dentiform expansion.
Genitalia. Not examined. Distribution. Widely distributed in the Amazon basin. Known from several localities along the Rio Negro (S. Venezuela), Rio Solimões (S. Colombia and Pará, Brazil), and their confluence, and the Rio Xingu (NE Mato Grosso, Brazil).
Derivation of name: Masculine. Greek noun, ammos (= "sand"), in reference to the habitat and coloration of the known species of this genus, and Tachys, the nominate genus of the subtribe Tachyina.
Remarks. Though these beetles are tentatively placed within Elaphropus due to the afoveate mentum, their remarkable (though perhaps homoplasious) resemblance to the foveae-bearing species Meotachys (Scolistichus) riparius, calls into question the long-assumed taxonomic value and phylogenetic distribution of this character. These two species have similarly broad, pan-Amazonian, apparently overlapping distributions. Molecular data should help to clarify whether their shared morphologies are due to convergence of separate lineages or the loss or gain of foveae within a lineage. Type locality. Brazil: Amazonas: Rio Solimões, Ilha de Marchantaria, 59°58'W 3°15'S. Description. Size, form, color, microsculpture, head, prothorax, mesothorax, and distribution as in description of the subgenus.
Derivation of specific epithet. The specific epithet marchantarius is a toponym referring to Ilha de Marchantaria, the collection locality of the majority of type material, located near Manaus, Brazil.
Diagnosis. Mentum without foveae; head with prominent keel-like frontoclypeal carina; elytral interneurs punctate, incomplete in length, and reduced in number; i8 visible only in apical half, interrupted and reduced.
Genitalia. Not examined. Distribution. Known only from the type locality of Santarém, Pará, Brazil. Derivation of name: Masculine. From the Greek adjective ídios (="self/peculiar"), in reference to its unique combination of characters, and Tachys, the nominate genus of the subtribe Tachyina.
Remarks. Based on its afoveate mentum and apicolaterally notched protibiae, the only known species of Idiotachys is considered to be part of the greater Elaphropus complex. The overall proportions, reduced and punctate elytral strial interneurs, reduced 8th interneur, and arrangement of humeral elytral ombilicate setae diagnostic for the species described below preclude its placement in any existing Elaphropus subgenus. These, along with unique external characters, support Idiotachys as a lineage distinct from either Tachyura or Barytachys, the two subgenera it most closely resembles.
Color. Glabrous, rufotestaceous to piceous; elytron with two pale maculae. Head. Mentum without foveae; frons without longitudinal depressions; frontoclypeal suture with very short lateral subfoveate grooves extending posteriad; apical half of antennae abruptly lighter that basal half, nearly white in many specimens.
Prothorax. Pronotum (Fig. 3H) narrowed at base, margins sinuate; posterior angle approximately square; lateral margin of pronotum narrowly explanate, with flange about 2× wider at midpoint than at base or apex and bordered by lateral groove; lateral groove extending to posterior angle; shallow, transverse basal impressions reduced to a series of several small, shallow punctules; basal two protarsomeres of male dilated, medially dentiform.
Derivation of specific epithet. Derived from the Latin occidens (="west"), in reference to the New World precinctiveness of this species. This subgenus was previously only described from the Old World.
Distribution. Old World and Australia, with a single species (P. laeva) in the Americas.
Distribution. Known from shoreline habitats along the Pacific coast of Costa Rica (Erwin 2004) and undescribed species from México to Colombia (Erwin in prep).
Microsculpture. Varied, from coarse/scaly/isodiametric to fine/linear/transverse. Head. Head with three pairs of supraorbital setae (Fig. 3B); mentum with paired circular or oval-shaped foveae, or with pair of shallow impressions; eyes reduced in most members; antennae submoniliform and densely setose; subapical labial palpomere conspicuously large and bulbous.
Abdomen. Terminal ventrite with two (male) or four (female) elongated setae. Genitalia. See Jeannel 1962. Distribution. Known from across South and Central America, México, the southeast United States (Alabama, Mississippi), Hawaii, and islands of the Caribbean (Puerto Rico, Cuba) with the greatest species diversity in the Amazon basin (Adis et al. 1986).
Head. (Fig. 3A) Antennae submoniliform; mentum with shallow foveae; head with two pairs of supraorbital setae; eyes reduced, each with about 12 large facets; frontoclypeal suture with small lateral subfoveate depressions; frons without longitudinal depressions; margin above antennal insertion prominent, with longitudinal bead; small dark puncture between gular sutures; labial palps very small, with subulate palpomere reduced or absent.
Abdomen. Ventrites densely punctate and moderately setose. Genitalia. Not examined. Distribution. Known only from the type locality in Loreto, Perú. Derivation of name: Masculine. Derived from the Greek noun stigma (="mark" or "puncture"), in reference to the coarsely punctate elytra of the lone representative of this genus, and Tachys, the nominate genus of the subtribe Tachyina. Description. Size, form, color, microsculpture, head, prothorax, pterothorax, abdomen, and distribution as in description of the genus.

Stigmatachys uvea
Derivation of specific epithet. Derived from the Latin noun uvea (="grape"), referring to the ovate shape of the elytra of the holotype in dorsal view.
Head. Mentum bifoveate; head with two pairs of supraorbital setae. Prothorax. (Fig. 3C) Pronotum with prominent, square to slightly acute posterior angles; basal section of pronotum triangular, with straight or curved transverse impressions meeting at base of median furrow; basal protarsomere of male dilated, medially dentiform.
Genitalia. (Based on male genitalia dissected and examined from single individuals of four different species) Male (Fig. 6B, C, F): overall form varied, median lobe with comb-like internal sclerites; both right and left parameres wedge-shaped, stout at base; left paramere large and broad with dark, sclerotized basal hook and 5 apical setae; right paramere smaller, with 4 or 5 apical setae. Female genitalia not examined.
Distribution. Known from North, Central, and Amazonian South America. Derivation of name: Feminine. Greek adjective nothos (="false/spurious"), in reference to this diverse and New World-restricted group's misleading taxonomic history, and deris (="fight" (Bousquet 2012)), from the name Polyderis. Members of this genus were previously classified within Polyderis based on a lack of useful and distinctive characters owing to their diminutive size; species of Nothoderis are restricted to the New World and are morphologically distinct from Polyderis (an old world genus with one species, P. laeva, widely distributed in North America).
Remarks. Species of Nothoderis are united by the shape of the pronotum, course of the eighth elytral interneur, features of male genitalia, form of the elytral apical recurrent groove, and preliminary molecular evidence. Male genitalia of Polyderis laeva were also examined and illustrated, and differ notably from all examples of Nothoderis in the form of the internal sclerite(s) and parameres (Fig. 6D). Polyderis laeva remains the sole new world representative of Polyderis s.str. based on external morphology; in addition, preliminary molecular evidence suggests that P. laeva belongs to a lineage phylogenetically distinct from that of N. rufotestacea and other representatives of Nothoderis. Rather, members of this gen. n. are affiliated with the Meotachys/Pericompsus complex (Maddison et al. in prep.).
Genitalia. Not examined. Distribution. Known from localities across the Amazon basin, from the upper Rio Negro system to the Rio Napo in Ecuador and northeastern Perú, and the lower Solimões River near Manaus.
Derivation of name: Masculine. From the Greek skolios (="crooked"), and stíchos (="line"/"row"), in reference to the diagnostic curved 8 th interneur. Derivation of specific epithet. Derived from Latin ripa (="river bank/edge"), in reference to the riparian habitats throughout the Amazon basin from which this species is known.
Prothorax. Pronotum (Fig. 3E) transversely quadrate or narrowed near base, with base and apex about equal in width, but greatest width about 1.5× as wide as narrowest width; lateral margin of pronotum markedly sinuate; anterior convergent impressions boldly impressed, not reaching medial furrow; basal transverse impressions deeply punctate, interrupted by small but deep medial excavation; basal section of pronotum opposite scutellum smooth, inflated; thin, medial furrow emerging from basal excavation not meeting anterior margin of pronotum; prosternum smooth, not sulcate.
Distribution. Known from the type locality in Ecuador, as well as 4 localities along the Rio Negro, northern Amazonas, Brazil, and southern Perú.
Derivation of name: Masculine. From the Greek hyle (="wood/forest", "matter/ substance"), in reference to the association of species of this genus with Amazonian inundation forest habitats and the unique suite of characters uniting the two species, and Tachys, the nominate genus of the subtribe Tachyina. Derivation of specific epithet. Latin rubrum (="red/crimson"), in reference to the deep red-brown color of this species.

Meotachys
Note: The holotype will be deposited in UNMSM and is currently held in trust until the completion of studies at NMNH.
Distribution. Australia and the Americas.
Distribution. Species of this subgenus are numerous and described from across the New World between the temperate mid-latitudes of North and South America and some of the Caribbean islands.
Distribution. Species of this subgenus are restricted to the New World, described from México south to Argentina and some of the Caribbean islands.

Discussion
Both species of the Meotachys subgenus Hylotachys described above are the first "bifoveate' (Ortuño and Arillo 2015) tachyines discovered to possess mesepisternal pits. These structures are highly varied in form and are found in "non-bifoveate" species throughout Elaphropus (Tachyura) and allied subgenera (incl. Tachylopha, Barytachys, Nototachys, and Sphaerotachys) (Erwin 1970), as well as a small subgenus of South American Bembidion (Maddison 2014) and certain Oodini (Spence 1982). Nearly all species known to possess these structures are hygrophilous. The waxy substance noted by Maddison (2014) in ethanol-preserved specimens was not observed in any of the specimens of Hylotachys examined, which were likely not ethanol-killed.
Previously synonymized under Polyderis (Erwin 1974b) and later considered a subgenus, Polyderidius Jeannel 1962 should be considered a separate genus, united by consistent morphological characters and distinct from Polyderis s.str. Species of Polyderidius are instead probably allied with Paratachys and Tachys s.str., based on the form of the elytral apical recurrent groove.
Relationships among groups within the subtribe Tachyina, in particular Elaphropus, remain a subject of contention and have been reviewed by several authors in recent decades. The conflicting taxonomic concepts proposed in previous reviews, classifications, and checklists (Lindroth 1966, Erwin 1974b, Shilenkov 2002, Kopecký 2003, Sciaky and Vigna-Taglianti 2003, Lorenz 2005, Bousquet 2012) represent alternative hypotheses waiting to be tested in a molecular context.
Due to their small size and a lack of resources for their identification, tachyines are easy to overlook or misidentify. A good deal of undescribed tachyine diversity is likely hidden in uncurated material, stored bycatch, and existing collections (Baehr 2016). In the Amazon Basin, ecosystem level processes are thought to have generated the rapid diversification apparent in this and other groups (Erwin and Adis 1978). Detailed collection data and large sample sizes exist for a number of New World species discovered through long term, bulk collecting efforts employing passive traps, leaf litter sampling, and canopy fogging (Erwin 1983(Erwin , 1984(Erwin , 1991. Much less is understood of the way of life, intraspecific diversity, and distribution of species described from small series and with limited representation in collections. Conservation status is difficult to estimate for such rarely collected taxa as Costitachys and Tachyxysta, especially for those known only from unique collecting events (e.g., Stigmatachys and Elaphropus (Idiotachys)). Moreover, anthropogenic impact to rapid-ly developing regions such as the Atlantic coast of South America has likely already affected the distribution and abundance of both described and undiscovered tachyine species.