Leuctra usdi, Grubbs, Scott A., 2010

Grubbs, Scott A., 2010, Leuctra usdi, a new stonefly (Plecoptera: Leuctridae) of the L. tenuis (Pictet) species group from the southeastern U. S. A. plus three new Alabama state records, Zootaxa 2498, pp. 59-64 : 59-63

Leuctra usdi sp. n.

( Figs. 1A –F, 2A)

Male. Forewing length 5.5 – 6.5 mm. General body color and wings brown. Cerci tubular and unmodified. Abdominal terga 1 – 6 unmodified. Lateral portion of abdominal segment 7 darkly sclerotized, conjoining medially into a near-parallel sided dorsal process that is ca. ½ segment width and truncate distally except for a pair of small lateral notches that give the process a slightly trilobed appearance, ends of the medial and lateral lobes terminate along the same distal plane ( Figs. 1A , 3A); lateral margins of abdominal segment 8 darkly sclerotized and conjoin medially only into a thin band anteriorly ( Figs. 1A–1B ). Epiproct sclerite narrow throughout length, expanded slightly and rounded distally. In lateral view the inner paraproct lobes are broad basally, simple, and rounded; with low tubercules present on both inner and outer margins distally ( Fig. 2 A– 2B); both the anterolateral and posteromedial portions are slightly concave. Outer paraproct lobes are broadest basally, simple and narrow, tapered distally and recurved slightly ( Fig. 2 A). Vesicle small and subtriangular ( Fig. 1C ).

Female. Forewing length 7.0 – 7.5 mm. Body color and cerci similar to male. Lobes of subgenital plate distally subtruncate, posterolateral corners rounded marginally and mediolateral corners slightly angular; lobes separated by a V-shaped notch ( Fig. 1D ).

Nymph. Unknown.

Material examined. Holotype male, U.S.A., Tennessee, Williamson Co., spring into Pinewood Branch, Leipers Fork, West Fork Harpeth River, 4 km W Leipers Fork, 35.8944°, -87.03878°, 15 III 2003, S.A. Grubbs ( SAG) and D. E. King ( INHS). Paratypes: same as Holotype but 1 male, 1 female (WKU); same as Holotype but 5 III 2007, 3 males, 2 females, SAG (WKU); Mayfield Spring, 9 km NW Leipers Fork, 35.9558°, -87.0754°, 5 III 2007, 1 male, 1 female, SAG (WKU). Alabama, Limestone Co., spring into unnamed tributary to Scarce Grease Branch, Sugar Creek, 2 km SE Lester, 34.9806°, -87.1309°, 18 II 2008, 2 males, SAG (WKU).

Etymology. The specific epithet is a Cherokee word for “small” or “little”, a reference to the diminutively-sized spring seep type locality. The Cherokee Native Americans formerly inhabited central Tennessee and northern Alabama.

FIGURES 3A–F. Scanning electron micrographs, male sclerotized process of 7th abdominal segment, dorsal view, 350X. A, Leuctra usdi , sp. nov.; B, L. carolinensis ( U.S.A., Maryland, Garrett Co., spring into Little Laurel Run, Savage River State Forest, 21 VI 1996); C, L. tenella ( U.S.A., Pennsylvania, Westmoreland Co., spring into Powdermill Run, Powdermill Nature Reserve, 3 VI 1993); D, L. tenuis ( U.S.A., Maryland, Allegany Co., Deep Run, Green Ridge State Forest, 7 VIII 1998); E, L. triloba ( U.S.A., Alabama, Clay Co., tributary to West Fork Hatchet Creek, Talladega National Forest, 25 I 2006); F, L. variabilis ( U.S.A., Tennessee, Carter Co., Twin Springs, Cherokee National Forest, 29 XI 2002).

Diagnosis. The combination of the well-defined process on the 7th abdominal tergum, smooth outer margins of the inner paraproct lobes and a small triangular vesicle places L. usdi in the L. tenuis species group ( Harper & Harper 1997) with L. tenuis , L. carolinensis Claassen, 1923 , L. tenella Provancher, 1878 , L. triloba Claassen, 1923 and L. variabilis Hanson, 1941 . Harper & Harper (1997) describe the dorsal process as “…notably beady in appearance…” which under higher magnification is manifested as raised scale-like structures distally (Figs. 3A–3F).

The inner and outer paraproct lobes of L. usdi are generally similar to L. triloba and L. variabilis ( Figs. 2 A–2F). All three species possess a small concavity in the anterolateral and posteromedial regions of the inner lobes. The inner lobes of L. usdi and L. triloba similarly have raised tubercles distally ( Figs. 2 A–2D) and the outer lobes are simple and recurved slightly ( Figs 2 A and 2C). The outer lobe of L. variabilis is not recurved as in L. usdi and L. triloba and the inner lobe tip bears fewer tubercules compared to the two other species. Nelson et al. (2002; Fig. 2 ) also showed that the outer lobes of L. variabilis from eastern Maryland were sickle-like and not recurved.

Leuctra usdi can be distinguished from the other members of the L. tenuis group mainly by characteristics of the 7th abdominal dorsal process ( Harper & Harper 1997). The subtruncate posterior margin of L. usdi is distinguished easily from the broadly rounded margins exhibited by both L. carolinensis (Fig. 3B) and L. tenella (Fig. 3C). The wide process of L. usdi is distinct from the distally subtruncate yet very narrow dorsal process of L. tenuis (Fig. 3D). Leuctra triloba exhibits variable forms of the 7th abdominal dorsal process ( Hitchcock 1974), yet the three lobes are rounded distally and do not terminate along the same distal plane (Fig. 3E).

Leuctra usdi appears morphologically most similar to L. variabilis . The latter species possesses a dorsal abdominal process that is similarly ca. ½ the width of the 7th tergum. The small lateral lobes of L. usdi terminate at the same plane as the larger medial lobe and all three lobes are subtruncate posteriorly (Fig. 3A). Leuctra variabilis typically lacks the small lateral notches along the posterior margin, giving the abdominal process a truncate appearance without distinction between lateral and medial lobes (Fig. 3F). Although rounded and marginally trilobed, variations of the dorsal process of L. variabilis occur ( Hanson 1941); the process is longer compared to L. usdi and this species emerges from late summer through autumn.

Remarks. The type locality is a small spring seep emanating from a hillslope in central Tennessee. This habitat is also the type locality for Soyedina alexandria Grubbs, 2006 . Leuctra usdi and S. alexandria were collected together in both 2003 and 2007. Allocapnia rickeri Frison, 1935 and S. alexandria were obtained with L. usdi from the Alabama locality.

Figures

FIGURES 2 A-F. Scanning electron micrographs, male paraproct, lateral view. A, Leuctra usdi, sp. nov., 350 X; B, L. usdi, sp. nov., 1500 X; C, L. triloba (U. S. A., Alabama, Clay Co., tributary to West Fork Hatchet Creek, Talladega National Forest, 25 I 2006), 350 X; D, L. triloba, 1500 X; E, L. variabilis (U. S. A., Tennessee, Carter Co., Twin Springs, Cherokee National Forest, 29 XI 2002), 350 X; F, L. variabilis, 1500 X.

FIGURES 1 A – D. Leuctra usdi, sp. nov. A, Male terminalia, dorsal view; B, Male terminalia, lateral view; C, Male terminalia, ventral view; D, Female terminalia, ventral view.