A review of the Nearctic genus Zealeuctra Ricker (Plecoptera, Leuctridae), with the description of a new species from the Cumberland Plateau region of eastern North America

Abstract The stonefly genus Zealeuctra (Plecoptera: Leuctridae) is endemic to the central and eastern Nearctic regions and is presently comprised of 10 species. Scanning electron microscopy (SEM) was used to examine and redescribe two important diagnostic features typically used to identify and define the adult male stage: the large, anteriorly-recurved epiproct and the medial cleft of the ninth abdominal tergite. SEM was also employed to depict the posteromedial portion of female 7th sternum. A new species, Z. ukayodi sp. n., is described from the Cumberland Plateau region of northeastern Alabama and Tennessee. The new species appears superficially similar to Z. talladega Grubbs, but is easily differentiated by characteristics of the male medial cleft. An updated taxonomic key to the males of Zealeuctra is provided.

Zealeuctra is endemic to the central and eastern Nearctic regions, and is typically associated with intermittent or temporary upland streams (Snellen and Stewart 1979;Stewart and Stark 2002). Zealeuctra claasseni and Z. fraxina are the only species distributed broadly. In contrast, three species are found mainly in the Texas Hill Country region (Z. arnoldi, Z. hitei, and Z. stewarti), three species are regional endemics within the Interior Plateau region (Z. cherokee, Z. wachita, and Z. warreni), Z. narfi is distributed from Arkansas and Missouri north to Wisconsin, and Z. talladega is known only from the Talladega Mountains region in eastern Alabama.
Zealeuctra exhibits several unique characteristics in the adult stage, namely the swollen male cerci with accessory humps and/or spines, the male ninth tergite bearing a conspicuous medial depression (i.e. "cleft"), and the female seventh sternite having a posteromedial lobe (although secondarily lost in two species; Ricker and Ross 1969). The two diagnostic features typically used to identify and distinguish between males are the (1) large, anteriorly-recurved epiproct and the (2) shape and sclerotization patterns of the cleft. The shape and arrangement of cercal lobes/spines can also aid with identifications (e.g. Poulton and Stewart 1991). In addition, the fused subanal platesanal probe structure appears to offer diagnostic information yet this has not been fully studied. Identifying females to species is markedly easier if associated males are present. Females are identified by the hind margin of the seventh abdominal sternite, notably the (a) presence or absence of a central notch and lobe and (b) shape of the "shoulders" if a notch is present. Zealeuctra nymphs are uncommon in collections and only one species has been described in detail (Z. claasseni; Stewart and Stark 2002).
In this study scanning electron microscopy (SEM) was employed to examine two diagnostic features of Zealeuctra males, focusing on the epiproct and the abdominal cleft. The posteromedial portion of the female seventh abdominal segment is also depicted with SEM micrographs. A new species is described herein and an updated taxonomic key to the males of Zealeuctra is provided. Ricker and Ross (1969, their figure 29) placed Zealeuctra in a polytomy with Paraleuctra Hanson, 1941, Rhopalopsole Klapálek, 1912, and Leuctra divisa Hitchcock, 1958 (the latter is now included in Paraleuctra (Stark & Kyzar, 2001)). They postulated that these taxa were grouped by two synapomorphies: females with an incomplete 10 th abdominal sternite and the presence of membranous pleural folds on larval abdominal segments 1-6 (shared also by Moselia Ricker, 1943, (Stewart andStark 2002)). Ricker and Ross (1969, their figure 28) proposed that the seven species of Zealeuctra recognized at that time were derived from a series of three basal ancestors, and that Z. narfi was the most ancestral species.

Results and discussion
Testing Ricker and Ross's (1969) hypotheses, however, and assessing how those species described since 1970 fit within an evolutionary framework is mostly beyond the scope of this paper. This would require a comparative morphological assessment of the fused subanal plates-anal probe structure, and arguably more importantly, a modern and robust phylogenetic analysis using molecular techniques (e.g. mitochondrial cytochrome c oxidase I gene sequencing).
An updated taxonomic key to the males of Zealeuctra is provided, and a new Zealeuctra species is described herein from the Cumberland Plateau region of southern Tennessee and northeastern Alabama. Ricker and Ross (1969) and Poulton and Stewart (1991)  Epiproct base narrowly triangular and with a minor shelf-like anterior projection ( Figure 5B); inner margins of cleft lacking crenulations and with only a single tooth-like medial projection in posterior half (Fig. 5A); known mainly from central Texas (Fig. 11)  Epiproct spine very long and slender (Kondratieff and Zuellig 2004, their fig. 2); endemic to south-central Texas (Fig. 13)  Epiproct comprised of two prominent spines, a large posterior spine plus an accessory anterior spine (Fig. 10B)  Description. Male -abdominal tergal cleft. Simple in outline. Anterior portion wide and broadly U-shaped, with a nearly straight terminal margin (Fig. 1A). Posterior portion narrowing slightly with no medial projections and only scarcely visible crenulations along inner margins. Male -epiproct. Base short and robust, narrowing slightly to a short, recurved, subtriangular spine (Figs 1B-C). A short, slightly concave projection extends anteriorly from the base to approximately the same plane as the spine. Base with bulbous posterior swelling, spine with small accessory posterior cusp that is low and nub-like.

Key to Zealeuctra males, modified in part from
Female -7 th sternum. Seventh sternum with a large, subquadrate lobe nested in a distinct, central notch. The notch is bordered laterally by large, convex "shoulders" (Fig. 1D Remarks. This species is somewhat superficially similar to Z. fraxina. Males are easily identified by the combination of the simple, U-shaped cleft and the presence of the anterior, concave cusp present at the base of the short, compact epiproct spine. The depiction of the posterior cusp as pointed and acute in Ricker and Ross (1969, their Fig. 2) is not accurate and typically not visible. The cusp tends to be low and nub-like. This species is known mainly from the Edwards Plateau of west-central Texas (Fig. 12). Zealeuctra cherokee Stark & Stewart, 1973: 192
Male -epiproct. Triangular base narrowing to anteriorly-recurved and tapering terminal spine, no accessory spine or swelling present (Figs 3E-H). Conspicuous tubercles located on the anterior margins of the triangular base. No accessory spine or cusp present.
Female -7 th sternum. Seventh sternum with a small, variably-shaped lobe nested in a small central notch (Figs 3I-3L). The lobe ranges in shape from somewhat quadrate to broadly convex. The notch is likewise variably shaped, from essentially straight and scarcely perceptible (    Remarks. Despite the broad distribution (Fig. 12), there appears to the little variation in the general features of the cleft. Only a minor degree of variation is evident in the epiproct, particular in the size and shape of the triangular base. Ricker and Ross (1969, their fig. 20) and Poulton and Stewart (1991, their fig. 112) depicted an epiproct base that is markedly broader than what is shown here with SEM micrographs. Description. Male -abdominal tergal cleft. Anterior portion wide and very broadly U-shaped, posterior portion also broadly rounded and bearing a slightly-concave serrated medial projection (Fig. 4A). Crenulations absent from inner margins of cleft. Male -epiproct. Triangular base narrowing somewhat to an anteriorly-recurved and tapering terminal spine; a small accessory posterior spine is present but manifested only as a cusp-like projection on some specimens (Fig. 4B).

Zealeuctra fraxina
Female -7 th sternum. Seventh sternum with a large, convex lobe nested in a distinct, central notch. The notch is bordered laterally by large, convex "shoulders" (Fig. 4C)  Remarks. Only Z. claasseni is distributed more broadly across the central and eastern US than Z. fraxina (Fig. 11;DeWalt et al. 2012). Additionally, this is one of only two species, Z. talladega being the other, that occur in the Appalachian Mountains. The Virginia record noted above was collected along the margins of Peaks of Otter Lake, but surprisingly several hundred meters from the nearest inlet or the only outlet (Little Stony Creek). Zealeuctra fraxina and Z. arnoldi are the only two species that bear a small subterminal cusp posterior to the tapering epiproct spine. Ricker and Ross (1969, their fig. 28) speculated that these two species, plus Z. wachita, share a common ancestor.

Male -epiproct.
Base slender and triangular, narrowing to anteriorly-recurved and tapering terminal spine, no accessory spine present (Fig. 5B). A small "step" (sensu Ricker and Ross 1969) demarks the base from the tapering spine. No accessory spine or cusp present.
Female -7 th sternum. Seventh sternum with a small, subtriangular lobe nested in a scarcely-concave central notch (Fig. 5C) Remarks. The form of the cleft of this species is nearly identical to Z. claasseni, and the epiproct is essentially a narrower form of that exhibited by Z. claasseni. Ricker and Ross (1969, their fig. 28) speculated that these two species share a common ancestor.
Female -7 th sternum. Seventh sternum with a broadly-subquadrate lobe nested in a scarcely-convex central notch (Fig. 6D). Posterior margins essentially straight. Remarks. Although the type locality for Z. narfi is in southern Wisconsin, this species is common and widespread only in the southern portion of its range, and par-ticularly in southern Missouri (Fig. 14). There are only three known locations for Z. narfi in Wisconsin (DeWalt unpublished data) and is likewise uncommon in Illinois, with only three collected localities between 1976 and 2000 (Webb 2002). There have also been several failed attempts by the senior author to locate this species in western and southern Indiana.

Male -epiproct.
Base very broad and subquadrate in shape, narrowing to anteriorly-recurved and broadly tapering terminal spine, no accessory spine present although a small subterminal posterior nub may be present (Figs 7D-F). Subquadrate base varies from rounded broadly to right angular in shape. No accessory spine or cusp present, but a minute, very low, medially-positioned hump is present along the anterior, recurved portion of epiproct (Figs 7D-F).
Anterior portion of male abdominal tergal cleft is narrowly U-shaped, and rounded along the anterior terminus. The posterior portion is widest anteriorly with crenulations present along inner margins. Overall shape of cleft ranges from either V-shaped to somewhat sinuous (Figs 8A-B, I). Epiproct base very broad and subquadrate in shape, narrowing to anteriorly-recurved and broadly tapering terminal spine, no accessory spine present (Figs 8C-E). Subquadrate base varies in from rounded broadly to right angular in shape. No accessory spine or cusp present. Cerci sclerotized mainly along outer margin and bearing a small dorsomedial hump and a subapical, triangular sclerotized tooth (Figs 8G-I). Length of vesicle ca. 1.5× width.
Female. Forewing length 7.5-8.0 mm; body length 6.0-8.0 mm. General body color brown. Seventh sternum with a quadrate sclerotized region, convex posteriorly, and scarcely projecting over the anterior portion of the eighth sternum (Fig. 8I); posteromedial portion unpigmented and very slightly notched, bearing a lightly-pigmented lobe that is convex posteriorly (Figs  Etymology. The specific epithet is a Cherokee word for "dry", a figurative reference to the temporary stream habitat characteristic of this species. Cherokee Native Americans formerly inhabited the southern Cumberland Plateau region. Diagnosis. The species is similar only to the cognate Z. talladega, and these two species can be separated mainly by characteristics of the male cleft. In Z. talladega, the cleft is highly sinuous or hourglass in shape and lacks the large crenulations along the inner margins. In Z. ukayodi, the cleft ranges from broadly V-shaped to somewhat sinuous, with large, conspicuous crenulations present along the inner margins of the posterior portion. Variation in the shape of the epiproct, namely the anterior quadrate or subquadrate shelf, overlaps between the two species. There is also a minute, medially-positioned hump present along the anterior, recurved portion of epiproct in Z. talladega (Figs 7D-F) that is lacking entirely in Z. ukayodi (Figs 8C-E). The fused subanal plates-anal probe of Z. talladega and Z. ukayodi appears to be highly similar in structure.
Remarks. Zealeuctra ukayodi appears to be restricted to the southern portion of the Cumberland Plateau, known at present from central Tennessee south to the type locality in northeastern Alabama (Fig. 13). The range of only one other Zealeuctra species, Z. fraxina, extends south and eastward into the Cumberland Plateau region in northeastern Alabama (Grubbs 2006 Description. Male -abdominal tergal cleft. Anterior portion broadly rounded, with a secondary U-shaped extension, inner margins set apart from remainder of cleft (Fig. 9A). Posterior portion markedly wider than anterior portion, interior margins rounded and lacking crenulations, terminating posteriorly as paired, large subtruncate medially-projected extensions. Male -epiproct. Base narrow and extending laterally (Fig. 9A), spine directed at ca. 90° angle from base, tapering gradually, and recurved somewhat anteriorly (Figs 9B-C). No accessory spine or cusp present. Female -7 th sternum. Seventh sternum with a small, subtriangular lobe nested in a slightly-concave central notch (Fig. 9D).
Material examined. USA, Arkansas: Scott Co., Johnson Creek, Hwy 49, 34.7131, -94.2101, 6.I.1999. Oklahoma: LeFlore Co., tributary to Big Creek, NW Page, Hwy 59/270, 34.7144, -94.5547, 6.II.2003 Remarks. This is the only Zealeuctra species that has a cleft bearing a secondary anterior extension. Zealeuctra wachita appears to be easily the least common of the three Zealeuctra species endemic to the Interior Plateau region. Poulton and Stewart (1991), in their study of the stoneflies of the Ozark and Ouachita Mountains, included only two Arkansas localities for this species. In contrast, the other two regional species, Z. cherokee and Z. warreni, plus Z. claasseni and Z. narfi, are markedly more common. The Oklahoma records noted above (Fig. 11)  Description. Male -abdominal tergal cleft. Anterior portion broadly-rounded and U-shaped. Posterior portion V-shaped, with small crenulations evident along inner margins, terminating posteriorly with paired, subtriangular, medially-projected extensions (Fig. 10A). Male -epiproct. Base broad and flanged laterally (Fig. 10A), with paired spines both originating from base, posterior spine ca. 2× length of anterior spine, moderately recurved anteriorly (Fig. 10B), anterior spine straight and bifurcated slightly at tip, with the paired terminal ends bearing four thick spines at tip (Fig. 10C).