Isoperla species A

(Figs. 1 a-h)

Material examined. OR: Linn County, Marion Creek, near confluence with Willis Creek, 44.60186°N, 121.93892°W, 17/V/2001, K.W. Stewart, B.P. Stark, J.B. Sandberg, 1♀ Larva; Marion Creek, Hwy 22 bridge, Marion Forks, 44.61457°N, 121.94859°W, 09/VI/2011, J.B. Sandberg, 1♀ Exuvia .

Body length of mature female larva 12.5 mm. Dorsum of head with contrasting pigment pattern and a mixture of fine light and dark clothing setae, anterior frontoclypeus margin unpigmented; light M shaped pattern anterior to median ocellus with median longitudinal light band extending almost to light frontoclypeus area, separated by thin light brown pigment band, lateral thin arms with nearly parallel margins connected to median light band, directed posteriorly and extending to antennal bases; posterior ocelli with completely enclosed small light areas along outer lateral margins; interocellar area partially light, somewhat triangular and completely enclosed by dark pigment, light area extending past posterior ocelli, not reaching dark pigment below the arms of the epicranial suture; occiput with irregular spinule band extending from behind eye to near median epicranial suture, completely enclosed by light brown pigment (Fig. 1a). Lacinia bidentate, total length 1619-1640 µm (Figs. 1e- h, Tables 1-2); apical ventral setae not arranged in rows like other western species, size ranging from long stout and striated to short and fine, concentrated apically forming a patch ranging from a thin continuous row to a wide concentrated band (Figs. 1 e-f); 18–20 setae begin as a single stout row along the outer ventral apical lacinia margin between AT inner margin and SAT outer margin, continuing as a submarginal band (2-3 setae wide) in front of SAT, plus 1 thin marginal seta (TMS) adjacent to AT inner margin (Figs. 1 g-h), dorsal seta (DS) absent; ventral apical setal band widening past the SAT inner margin (Figs. 1 g-h); ventral apical setal band thickest and individual setae longest near the junction of apical and inner palm margins (Figs. 1 e-f); ventral apical setal band continues toward base along inner lacinia margin, setae abruptly decrease in size and concentration before reaching the middle of inner margin, and the smallest sparsely concentrated setae end at approximately ¾ the inner lacinia margin length (Figs. 1 e-f); dorsal surface setae (DSS) form a thin sparse band projecting at a slight angle from the apical margin, the first DSS located below SAT inner margin, sparse band continuing along apical and inner palm margins, ending before posterior-most ventral surface setae, best observed un-mounted under dissecting microscope. Galea with 42 setae in thick ventral row, apex with 2 setae. Maxillary palp segments 2–3 with curved, apically rounded setae. Pronotum with median longitudinal light area bisected by central irregular brown bands and bordered by wide dark bands typical of the I. marmorata complex; discs each with a few variable dark rugosites concentrated along inner margins of dark brown bands and fine dark clothing setae distributed mostly upon dark pigment, lateral margins with broad light bands (Fig. 1b). Meso and metanotum with contrasting pigment pattern and fine dark clothing setae (Fig. 1c). Legs with numerous fine golden clothing setae and scattered erect spines on outer surface of femora, erect spines longest and concentrated along dorsal and two longitudinal ventral surfaces; fine silky setae sparse on dorsal surface of femora, numerous and continuous on tibia; distal femora with light transverse band, proximal tibia with dark transverse band. Abdominal terga with three longitudinal dark stripes (Fig. 1d); a pair of sub-median light areas enclosed by dark pigment form a wide light median longitudinal band bisected by median dark pigment; lateral pair of dark longitudinal stripes extending to lateral abdominal margins; scattered fine light clothing setae and erect spines dorsally; posterior margin with scattered long and numerous short spines in a concentrated row.

Distribution. Oregon, near eastern Mt. Jefferson Wilderness.

Diagnosis. There is no other known western Isoperla species with setae arranged in a large and continuous patch on the ventral lacinia surface. The known western Nearctic species have marginal and submarginal ventral setae arranged in a continuous or interrupted row along the apical or inner margins of the larval lacinia (Table 1).

Remarks. Isoperla species A larvae co-occurred with I. marmorata Needham & Claassen, I. sobria (Hagen), and an unidentified Isoperla species female without an extended subgenital plate.