Description of a new species of Platynus Bonelli from the Appalachian Mountains of eastern North America (Coleoptera, Carabidae)

Abstract A new species of the genus Platynus Bonelli, Platynus daviesi, is described from specimens collected in the Appalachian Mountains. The species is structurally most similar to Platynus parmarginatus Hamilton but differs in having the coloration of the body dorsally darker on average, the elytra proportionally longer and wider, the vertex and disc of pronotum with well impressed microsculpture, the elytral interval 3 with four or five discal setae in most specimens, and the median lobe of aedeagus less curved overall. DNA barcoding was performed on several species of eastern North American Platynus species and Platynus daviesi was found to be genetically distinct from Platynus parmarginatus. A key to the 12 species of Platynus found east of the Mississippi River is provided.


Introduction
The genus Platynus Bonelli is a large, inadequately understood, and probably polyphyletic group belonging to the tribe Platynini. In Mexico alone, the genus contains an estimated 300 species (Liebherr and Will 1996: 301). The North American (north of Mexico) Platynus are much less diversified and relatively well known. Lindroth (1966, as the decentis and hypolithos groups included in the genus Agonum) treated all species then known except those restricted to the southwest and P. prognathus Van Dyke, an aberrant species known only from the holotype collected on Saint Simon Island, in southeastern Georgia. Liebherr and Will (1996) described three new species and presented a key to all 22 species found in North America north of Mexico.
While curating the Nearctic carabids of the Canadian National Collection of Insects, I found that two species were mixed under the name Platynus parmarginatus Hamilton. The purpose of this paper is to describe the unnamed species.

Material and methods
All the specimens reported in this study belong to the Canadian National Collection of Insects, Ottawa, Ontario (CNC), the Carnegie Museum of Natural History, Pittsburgh, Pennsylvania (CMNH), and the University of New Hampshire Collection, Durham, New Hampshire (NHDE). No attempt was made to locate further specimens in other collections.
The following measurements were taken on several specimens of the new species and P. parmarginatus: length of the head (LH) from the anterior edge of the clypeus at middle to an imaginary line between the posterior edges of the eyes; width of head (WH) across the eyes; length of pronotum (LP) along the midline; maximum width of pronotum (WP); length of elytra (LE) measured from the tip of the scutellum to the apex of the right elytron; and maximum width of elytra (WE). The standard body length [SBL = LH + LP + LE] was used to express the body length.

Platynus daviesi
Geographical distribution. As far as known, this species lives mainly along the Appalachian Mountains, ranging from Connecticut and southern Pennsylvania to northwestern Alabama (Fig. 4).

Habitat. Based on information attached to specimen labels, this species is probably an inhabitant of deciduous forests.
Dispersal Power. The wings are fully developed and no doubt functional. Several specimens were collected at ultraviolet light.
Comments. The new species is most similar to Platynus parmarginatus Hamilton and P. tenuicollis (LeConte). Adults of P. parmarginatus differ from those of P. daviesi by the following character states: size smaller (SBL: 7.2-8.9 mm; mean= 8.2 mm; n=20) on average; coloration paler on average, more reddish; elytra proportionally shorter and, on average, proportionally narrower (see Table 1); vertex without evident microsculpture meshes; disc of pronotum without or with shallowly impressed, more or less distinct microsculpture microlines; elytral interval 3 with four or five discal setae on both sides in most specimens (77/88 = 88%), rarely with three on one (9/88 = 10%) or both sides (2/88 = 2%); median lobe of aedeagus more curved overall (Fig. 3). Platynus parmarginatus is found mainly west of the Appalachian Mountains (Fig. 4); I have seen specimens of that species from Pennsylvania (Allegheny County), Indiana (Perry County), Illinois (Union County), Missouri (Franklin County), Arkansas (Franklin, Newton, Pope, Stone, and Washington Counties), and Oklahoma (Cherokee County). Both species are sympatric in southwestern Pennsylvania.  While most specimens of P. daviesi are easy to distinguish from those of P. parmarginatus, those seen from southwestern Pennsylvania are structurally less distinct. The microsculpture on the vertex and disc of pronotum is less evident on average and the body proportions not so clearly segregated. Nevertheless, all specimens seen could be identified with confidence.
Regarding Platynus parmarginatus, Krinsky (1989) pointed out that the median lobes of the aedeagi of his Connecticut specimens did not resemble the median lobe illustrated by Lindroth (1966). In fact, the median lobe illustrated by Krinsky (1989: fig. 1) is that of P. daviesi while that, extracted from a syntype, illustrated by Lindroth (1966: fig. 323b) belongs to P. parmarginatus.
Adults of Platynus tenuicollis differ from those of P. daviesi in having the meso-and metatarsomeres 1-3 each with a well-defined dorsal keel and the laterobasal impressions of the pronotum impunctate. Platynus tenuicollis is morphologically variable, for example in the elytral microsculpture, and may consist of more than one species. CO1 sequences were analyzed for 46 specimens of Platynus representing 11 species (Fig. 5). All barcoded specimens clustered congruently with their respective, morphologically defined species. Mean interspecific divergences ranged from 2.59-15.12% (Table 2). The intraspecific variation ranged from 0.00-1.32% (Table 2), except in P. angustatus which tabulated at 2.91% suggesting that possibly more than one species are assigned under this name. Indeed, Lindroth (1966: 646) pointed out that the apex of the median lobe in this species varies considerably in length, which is unusual in North American Platynus species. Specimens of P. daviesi were 2.69% divergent from P. parmarginatus, which is close to the divergence observed between P. trifoveolatus and P. parmarginatus (2.98%), two species that have long been separated on the basis of morphological differences. It is interesting to note that P. trifoveolatus, a morphologically quite isolated species within the eastern North American Platynus (see Lindroth 1966: 641), is the species genetically closest to P. daviesi (2.59%) among the 11 species analyzed (Table 2).
In order to help with identifying specimens of the new species, a key to all known eastern Platynus species is given.