Isogenoides Klapálek

Isogenoides are large perlodids that are very similar with Hydroperla Frison, from which it differs from the later by characters of the male and nymphs. John Sandberg's revision of this genus has recently been published with Ken Stewart (2005), and the key and species descriptions below are from this important work. They have noted that diagnostic characters for females - unless associated with males or long-term emergence data exist from a particular site - should be viewed with caution due to intraspecific variation of the subgential plate, upon which morphological identification relies. (I wish to thank Drs. John Sandberg and Ken Stewart for granting permission to use the material from their publication for this page).

Eight species are known from North America, of which four are found in Michigan. Isogenoides krumholzi Ricker, also recorded from Michigan, has been synonomyzed with Isogenoides doratus (Frison) (Sandberg and Stewart 2005).

Adults

1a	Males	2
1b	Females	5
2a(1a)	a. Apical process divided into two anteriorly directed, partially sclerotized hooks (Fig. 1)	Isogenoides olivaceus (Walker)
	b. In lateral view, posterior margin of epiproct with long, curved, lashlike tabular spine arising from just above mid-length
Fig. 1 Fig. 2
2b	a. Apical process not divided anteriorly, completely sclerotized as a single hook or with groove	3
	b. In lateral view, posterior margin of the epiproct without a long lash-like spine
3a(2b)	Posterior margin of epiproct with paired, ventrally directed hooks or spines (can be difficult to see if epiproct not everted or extended, some dissection of the membranous cowl covering the lateral stylets may be required)	Isogenoides frontalis (Newman)
	also: Epiproct apical hook short, its extension from epiproct less than epiproct width in lateral view; In dorsal view, hemitergal lobes connected anteriorly by large membranous area to mesoanterior winglike internal basal anchor sclerites, the inner-posterior angles of lobes forming obtuse or are evenly curved angles; inner-rounded margins of distal-most anteriorly directed lobes in contact at most, anteriorly; head without yellow area extending from posterior margin into ocellar triangle; apical 1/3 of lateral stylets in lateral view above widely expanded region, with margins sub-triangulate, gradually tapering to apex, forming bluntly pointed tips; in most non-everted specimens in dorsal view
3b	Posterior margin of epiproct without paired, ventrally directed hooks or spines	4
4a(3b)	a. Apical process of epiproct modified, with deep internally sclerotized groove	Isogenoides varians (Walsh)
	b. Paired, ventrally directed hooks on posterior margin heavily sclerotized, stout, their position from apex about 1/5 to 1/6 total epiproct length in lateral view
4b	a. Apical process of epiproct with single, stout, posteriorly, or posteriorly and ventrally directed hook	Isogenoides doratus (Frison)
	b. Paired, ventrally directed spines on posterior margin lightly sclerotized, slender, their position from apex 1/3 to 1/6 total epiproct length in lateral view
	also: Paired, ventrally directed posterior epiproct hooks slightly sclerotized and short (easily obscured by folding of epiproct tissue in cleared or older specimens), their position from apex about 1/3 to 1/2 total epiproct length in lateral view
5a(1b)	a. Posterior margin of subgenital plate posterior margin broadly rounded, with a deep, U or V-shaped notch, reaching approximately to point of overlap with Ab9 sternum	Isogenoides frontalis (Newman)
	b. Subgenital plate broad at base, its width approximately 3/4 width of Ab8 sternum, and produced from 1/4 to 3/4 length of 9th ternum
5b	a. Subgenital plate otherwise	6
	b. Subgenital plate, when present, with posterior emargination smaller than above, not reaching anteriorly to the point of overlap with sternum nine
6a(5b)	Subgenital plate produced from 3/4 to entire length of Ab9 sternum	Isogenoides varians (Walsh)
	also: Posterior emargination variable, usually with slightly produced protrusion, sometimes emarginated, vestigial or absent; cerci, antennae, femur-tibia joints and wing veins all dark brown, almost black in recently preserved specimens
6b	Subgenital plate produced from 1/3 to 2/3 length of Ab9 sternum	7
7a(6b)	a. Subgenital plate broad at base, its width approximately 3/4 width of Ab8 sternum	Isogenoides doratus (Frison)
	b. Posterior margin of plate variable, with small, slightly protruding nipple-like knob
	c. Small, slightly rounded emargination, or with margin entire
7b	a. Subgenital plate moderately broad at base, its width usually less than 3/4 width of 8th sternum	Isogenoides olivaceus (Walker)
	b. Posterior margin of plate variable, with either a broad-shallow, or narrow-moderately deep emargination

Mature Nymphs

Species Descriptions (from Sandberg and Stewart (2005))

Isogenoides doratus (Frison)

Male.— Macropterous. Length of forewings 13–14.5 mm; length of body 13–17 mm. General body color brown to dark brown. Head. Dorsum of head with rounded, light area offset from mesoanterior margin by thin brown band along anterior margin (Fig. 38); large yellow, broadly rounded area with base along posterior margin of head, extending mesoanteriorly to intersection of epicranial sutures. M-pattern raised, without setae, dark brown throughout most of pattern, beginning to fade to light brown and yellow just past anterior-most portions, these blending in pigmentation with light anterolateral areas of frons, distolateralmost, posteriorly directed legs intercept lateral wrinkled areas along inner margins of antennal bases (Fig. 38). Interocellar area brown with dark brown pigment entering laterally, dark brown areas connecting lateral ocelli to anterior ocellus, extending towards eyes, ending below large, lateral, medium brown rugosities; medium brown areas above dark brown areas; dark and medium brown areas form two, wide, slightly angled, longitudinal bands extending mesoanteriorly from lateral ocelli to inner, posterior margins of M-pattern (Fig. 38). Thorax. Pronotal median longitudinal yellow stripe with small amounts of variable pigment along dorsal suture, generally stripe widest posteriorly, tapered slightly anteriorly to posterior margin of anterior transverse furrow, then expanded laterally inside and above the furrow (Fig. 38). Abdomen. Dark brown with thin dark brown to black transverse stripes along anterior margins, normally overlapped by preceding segment’s posterior margin; first two terga with variable-shaped unpigmented areas, hemitergal and subanal lobes light brown to dark brown; dorsum entirely covered with dense, short, clear clothing setae not becoming longer on posterior, slightly expanded segments, except longer on hemitergal lobes; dorsolateral humps on terga 6–9 small, hardly evident in dorsal view, posterolateral margins of 7th tergum slightly swollen laterally, not posteriorly, posterolateral swollen area of tergum 8 with narrow transverse patches of slightly longer, golden, hair-like setae (Fig. 32, 33). Hemitergal lobes in dorsal view with lobe apices directed medially and posteriorly, apical margins broadly rounded, connected anteriorly by large membranous area to mesoanterior wing-like internal basal anchor sclerites (Fig. 33); 16–20 golden, mostly long, stout spinulae (sensilla basiconica) concentrated along anterior distal sclerite margin (Figs. 32, 33); short, dark, erect setae scattered posteriorly on lobe apex continuing laterally and anteriorly, these interspersed within long, numerous, golden, hair-like setae concentrated along posterior margin of lobe apex. Epiproct apex in lateral view with single, stout, posteriorly directed hook, its extension from epiproct less than epiproct width in lateral view (Figs. 34, 45, 46); posterior margin with slightly sclerotized pair of short, ventrally directed hooks, their position from apex about 1/3 to 1/2 total epiproct length in lateral view; in lateral view, under high magnification, anterior portion of epiproct with long, apically curved, moderately narrow, sharply tipped, scale-like setae, lateral margins with deep apically angled serrations (Fig. 47); anterior support sclerite trifid in anterior view, lateral arms as long as or slightly longer than base (Fig. 37), median arm approximately 1/2 as long as base, lateral arms in lateral view curved anteriorly at apex, giving appearance of anterior hooks (Figs. 34, 45), median arm wide at base, tapered gradually to sharp pointed apex ending before reaching 1/2 length of entire epiproct (Fig. 37); posterior support sclerite single, stout, long and tapered, with irregular-shaped hole at base below lateral membranous epiproct portions, lateral margins tapering slightly, then expanding slightly, to join laterally at about 1/2 to 2/3 total epiproct length from base to pair of short, lightly sclerotized, ventrally directed hooks, support sclerite continuing dorsally, tapering again gradually to broad apical point, ending near base of apical hook (Fig. 36). Internal basal anchor in anterior view hour glass-shaped with wide base tapering gradually to where anterior keel-like sclerite connects, expanding laterally into long, rounded lateral plates (Fig. 35); small, dorsal winglike triangular sclerites directed posterolaterally from centrally located, wide, rounded notch. Lateral stylets in lateral view with long, narrow base (Fig. 34); expanded areas at nearly 2/3 total length from base, parts of expanded region lightly sclerotized, barely visible along inner and dorsal margins; apical 1/3 narrow at expanded region, margins tapering gradually to narrowly rounded tips, angled margins minutely serrate; in anterior or posterior view, stylet appearing slightly wider than in lateral view (Figs. 36, 48); apical portions smoothly curved, apices directed dorsally. Aedeagus membranous with pair of distinct lateral lobes at dorsolateral apical margins (Figs. 40, 41); tiny, clear, erect setae sparsely scattered over entire surface of lateral lobes; two smaller pairs of lobes dorsally and ventrally, close to distal margin (Figs. 40, 41).
Female.— Macropterous. Length of forewings 15.5–17 mm; length of body 15–19 mm. General body color, and head-pronotal pigmentation patterns similar to male. Subgenital plate broad at base, its width approximately 3/4 width of 8th sternum, produced from 1/3 to 2/3 length of 9th sternum; broadly rounded posterior margin with variable mesoposterior characters (Figs. 39, 49): 1. mesoposterior margin of subgenital plate with small, slightly protruding nipple-like knob, 2. mesoposterior margin of subgenital plate with small, slightly rounded emargination, 3. mesoposterior margin of subgenital plate with a small, emarginated, slightly protruding double nipple-like knob, and 4. posterior margin of subgenital plate entire; dark pigmentation mostly anterior and lateral with two, smaller dark brown markings on plate, below mesally-angled posterior margins of abdomen, these markings enclosed by larger light brown markings.
Nymph.— General body color light brown to yellow with light and dark markings (Fig. 31). Head. Dorsum with contrasting pigment pattern; fine, long, dark clothing setae densely scattered; light colored narrow band forming M-pattern between antennal bases and median ocellus open mesoanteriorly; anterior transverse brown band reduced to two short, thin, anteriorly curved bands beginning along anterolateral margins, incompletely enclosing M-pattern anteriorly; anterior margin usually with broad transverse light band, generally extending mesoposteriorly to median ocellus, sometimes this area with faded light brown pigment, brown bands below partially enclosing M-pattern without two light areas; two small, irregular-shaped dark markings on anterolateral margins between antennal bases and labrum; labrum with two semicircular dark markings along anterior margin. Interocular area brown, sometimes with variable, mesoposterior light brown marking extending posteriorly from below anterior ocellus to epicranial intersection; post ocular and occipital spinule rows thin with many peg-like spinulae, longer, stout, spine absent in occipital row near post ocular row junction; occipital spinule row sometimes interrupted by small gap. Left and right mandibles under high magnification with ventral basal margin of distal-most cusp with short, indistinct row of small denticles reaching about 1/2 length of cusp (Fig. 4). Thorax. Pronotum covered with moderately dense, long, dark, clothing setae. Abdomen. Abdominal terga with distinct, dark, anterior, transverse bands on segments 2–10, segment one usually all brown except small, rounded, light area at mesoposterior margin, 10th tergum usually similar to 9th; long, dark, clothing setae interspersed between stout spines. Posterior setal row of male 8th abdominal sternum usually interrupted mesally in mature nymphs.

Isogenoides frontalis (Newman)

Male.— Macropterous. Length of forewings 15–17 mm; length of body 17–19 mm. General body color brown to dark brown. Head. Dorsum of head with thin light area along mesoanterior margin (Fig. 77); large yellow, nearly triangular area with base along posterior margin of head, extending mesoanteriorly to intersection of epicranial sutures. M-pattern raised, without setae, dark brown pigmentation beginning at anterior ocellus, fading to light brown and yellow at anterior-most portions, these blending in pigmentation with light anterolateral areas of frons, distolateral-most, posteriorly directed legs intercept lateral wrinkled areas along inner margin of antennal bases (Fig. 77). Interocellar area variable, usually brown with dark brown pigment entering laterally, sometimes completely darker than background, dark brown areas when present, connect lateral ocelli to anterior ocellus, extending towards eye, ending below large, lateral, medium brown rugosities; dark brown areas form two, wide, laterally directed bands, extending anterolaterally from lateral ocelli, reaching at least lateral wrinkled areas (Fig. 77). Thorax. Pronotal median longitudinal yellow stripe with small amounts of variable pigment along dorsal suture, generally stripe bowling pin-shaped (Fig. 77). Abdomen. Brown with thin dark brown to black transverse stripes along anterior margins, normally overlapped by preceding segment’s posterior margin; first tergum with variable-shaped unpigmented areas, apices of hemitergal and subanal lobes light brown to yellow; dorsum entirely covered with dense, short, clear clothing setae becoming longer on posterior expanded segments; dorsolateral humps on terga 6–9 expanded into paired pin cushion-like swellings, those on 7th segment largest, sometimes extending beyond anterior margin of segment eight, covered with long, clear to golden, thin clothing or hair-like setae (Fig. 70, 71). Hemitergal lobes in dorsal view of everted specimens with lobe apices directed medially and anteriorly, inner-posterior margins usually broadly rounded, appearing obtuse (Fig. 71); non-everted specimens with distal-most, anteriorly directed lobes generally in contact mesoanteriorly at most, inner-posterior margins usually evenly curved; connected anteriorly by large membranous area to mesoanterior wing-like internal basal anchor sclerites (Fig. 70, 71); 26–42 golden, mostly short, stout spinulae (sensilla basiconica) concentrated along anterior distal sclerite margin (Figs. 70, 71); short, dark, scattered, erect setae and long, clear, moderately dense, fine setae concentrated along posterior and inner margins. Epiproct apex in lateral view with single, stout, dark brown, posterior and ventrally directed hook, its extension from epiproct less than epiproct width in lateral view (Figs. 72, 83, 84); posterior margin without pair of ventrally directed sclerotized hooks; in lateral view, under high magnification, anterior portion of epiproct with long, apically expanded, round tipped, scale-like setae, lateral margins without serrations (Fig. 85); anterior support sclerite trifid in anterior view, lateral arms longer than base (Fig. 75), median arm subequal, lateral arms in lateral view curved anteriorly at apex, giving appearance of anterior hooks (Figs. 72, 83, 84), median arm narrow, tapered to sharp pointed apex ending approximately at 1/2 length of entire epiproct (Fig. 75); posterior support sclerite single, stout, long and tapered, with irregular-shaped hole at base below lateral membranous epiproct portions, lateral margins tapering gradually from base to approximately 1/2 length of total epiproct, margins subequal to nearly 3/4 total length from base, tapering gradually to narrow distal portion, joining inner, posterior margin of apical hook (Fig. 74). Internal basal anchor in anterior view wide base tapering inwards at lower 1/4 length, gradual outwards taper to approximately dorsal 1/2 length where anterior keel-like sclerite connects, gradually expanding into small, pointed lateral plates (Fig. 73); large, dorsal wing-like triangular sclerites directed posterolaterally from centrally located, narrow, elongated plate. Lateral stylets in lateral view with long, narrow base (Fig. 72); expanded areas variable, at nearly 2/3 total length from base, apical 1/3 wide, irregular-shaped at expanded region, margins sub-triangulate, tapering to bluntly pointed tips; in anterior or posterior view, stylets appearing slightly wider than in lateral view (Figs. 74, 75); apical portions irregularly-curved, apices angulate, directed laterally; Aedeagus membranous with pair of distinct lateral lobes at dorsolateral, apical margins (Figs. 78, 79); tiny, clear, erect setae sparsely scattered over entire lateral lobe margins; two smaller lobes dorsally, close to distal margin, may not be fully everted, their inverted bases only visible (Fig. 78); ventral wide, broadly rounded lobe projects slightly from distal margin.
Female.— Macropterous. Length of forewings 17–19 mm; length of body 17–19 mm. General body color, and head-pronotal pigmentation patterns similar to male. Subgenital plate broad at base, its width approximately 3/4 width of 8th sternum, produced from 1/4 to 3/4 length of 9th sternum, broadly rounded posterior margin with variable, deep, mesoposterior notch, from U to V-shaped (Figs. 76, 87); dark pigment patterns variable, from almost entirely brown to almost entirely yellow, consistently with two smaller dark markings on plate, below mesallyangled posterior margins of abdomen.
Nymph.— General body color brown with light and dark markings (Fig. 69). Head. Dorsum with or without contrasting pigment pattern, sometimes mostly brown to dark brown; fine, short, clear, clothing setae usually sparsely scattered to absent; when present, light colored narrow band forming M-pattern between antennal bases and median ocellus, sometimes all brown; anterior transverse brown band thick, completely enclosing M-pattern anteriorly; anterior margin with narrow transverse light band, brown area below, enclosing M-pattern with two small transversely flattened light areas above anterior-most portions of M-pattern; two small, irregular-shaped dark markings on anterolateral margins between antennal bases and labrum; labrum with two semicircular dark markings along anterior margin, two larger, faint, semicircular dark markings along posterior margin, some specimens with markings diffuse, narrowly connected. Interocular area brown, sometimes with variable, mesoposterior light brown marking extending posteriorly from below anterior ocellus to epicranial intersection; post ocular and occipital spinule rows thick with numerous peg-like spinulae, usually with one longer, stout, spine in occipital row near post ocular row junction. Left and right mandibles under high magnification with ventral basal margin of distalmost cusp variable, usually short indistinct row of small, vestigial denticles, occasionally distinct row of large, sharp denticles reaching about 1/2 length of inner margin (Fig. 6). Thorax. Pronotum covered with moderately sparse, short, clear, clothing setae. Abdomen. Abdominal terga with distinct, dark, anterior, transverse bands on segments 2–8, segment one all brown except small, rounded, light area at mesoposterior margin, 9th and 10th terga with variable-shaped mesoposterior light areas, preserved specimens may appear all brown, all yellow, or sometimes with thin posterior dark bands where anterior margins lie over ventral margins; short, clear, clothing setae interspersed between stout spines. Posterior setal row of male 8th abdominal sternum interrupted mesally in at least mature nymphs.

Isogenoides olivaceus (Walker)

Male.— Macropterous. Length of forewings 13–15 mm; length of body 15–16 mm. General body color brown to dark brown and black. Head. Dorsum of head with mesoanterior margin brown to light brown (Fig. 114); large yellow area with base along posterior margin of head, extending mesoanteriorly forming slightly truncated area, a second lateral, angled area below posterior margin of eye. M-pattern raised, without setae, dark brown throughout most of pattern, pattern not fading or blending into light brown or light anterolateral areas of frons; distolateral-most, posteriorly directed legs intercept lateral wrinkled areas along inner margins of antennal bases (Fig. 114). Interocellar area brown variable, usually brown with dark brown pigment entering laterally and light brown median stripe, dark brown irregular-shaped areas connecting lateral ocelli to anterior ocellus variable, extending directly to large, lateral, medium brown rugosities, or sometimes anteriorly to posterior margin of M-pattern; dark brown areas usually form two short, posterolaterally directed bands, or sometimes two wide, slightly angled, longitudinal bands connecting to inner legs of M-pattern (Fig. 114). Thorax. Pronotal median longitudinal yellow stripe with small amounts of variable pigment along dorsal suture, generally stripe widest posteriorly, tapered slightly anteriorly to posterior margin of anterior transverse furrow, then expanded laterally inside and above the furrow (Fig. 114). Abdomen. Dark brown with thin dark brown to black transverse stripes along anterior margins, normally overlapped by preceding segment’s posterior margin; first tergum with variable-shaped unpigmented areas, dorsal areas of terga 7–9, hemitergal and subanal lobes with some light brown to yellow pigment; dorsum entirely covered with long, clear, moderately dense, clothing setae; posterior margin of 8th tergite with longer, partially erect clothing setae. Dorsolateral humps small, variable, usually restricted to terga 7–8, visible in dorsal view; posterolateral areas of 7th – 8th terga slightly swollen dorsally, rarely laterally, not posteriorly, swollen areas of 8th tergite largest, sometimes with thin transverse dorsal yellow marking near posterior margin; narrow transverse patches of partially erect clothing setae along posterior margin of hump (Fig. 108, 109). Hemitergal lobes in dorsal view with lobe apices directed medially and slightly posteriorly, apical margins broadly rounded, connected anteriorly by moderately large membranous area to mesoanterior wing-like internal basal anchor sclerites (Fig. 109); 38–42 reddish-brown, mostly long, stout spinulae (sensilla basiconica) concentrated along anterior distal sclerite margin (Figs. 108, 109); short, dark, erect setae sparse on posterior membranous portion, these interspersed within long, numerous, golden, hair-like setae covering entire posterior areas; 10th sternite dark brown. Epiproct apex modified in lateral view with double, stout anteriorly and ventrally directed hooks, their anterior extension from epiproct less than epiproct width in lateral view (Figs. 110, 121, 122); posterior margin with single, curved, long, lash-like, dorsally directed process, its position from apex about 1/3 total epiproct length in lateral view; in lateral view, under high magnification, anterior portion of epiproct with long, apically irregular, wide, variably-tipped, scale-like setae, apical tip pointed, broad to narrowly bifurcate, or multiple serrated (Fig. 123); anterior support sclerite modified in anterior view, median arm wide, attached to base normally, lateral arms separated from median arm, extending dorsally to where they connect to ventral margins of double apical hooks (Figs. 112); posterior support sclerite modified, stout, wide at base, extending dorsally and laterally, forming partially membranous plate with two apical, small, sclerotized dorsolateral margins that partially occlude posterior portions of lateral stylets, base with irregular hole slightly more dorsal than normal, dorsal portion of anterior support sclerite modified, projecting posteriorly and dorsally away from membranous epiproct, tabular sclerite curls posteriorly and anteriorly forming progressively smaller coil (Fig. 111). Internal basal anchor in anterior view with narrowly expanded base tapering gradually to where anterior keel-like sclerite connects, expanding laterally into small, pointed, lateral plates (Fig. 113); long, slightly curved, dorsal wing-like triangular sclerites directed laterally from centrally located narrow notch. Lateral stylets in lateral view with long, narrow base (Fig. 110); expanded areas widely rounded at nearly 3/4 total length from base, apical 1/4 wide, irregular-shaped at expanded region, margins tapering gradually and curves posteriorly to sharply pointed tip; in anterior or posterior view, stylets appear slightly wider in than in lateral view (Figs. 121, 136); apical portions smoothly curved, apices directed slightly laterally. Aedeagus membranous with pair of distinct lateral lobes slightly below dorsolateral apical margins (Figs. 108, 109); two smaller lobes located and directed dorsally on aedeagus, situated between lateral lobes (Fig. 109); tiny, clear, erect setae sparsely scattered over entire surface of small, dorsally directed lobes; one wide, low, rounded knob located mesally and apically as seen in dorsal view.
Female.— Macropterous. Length of forewings 16–18 mm; length of body 17–20 mm. General body color generally lighter, and head-pronotal pigmentation patterns similar to male. Subgenital plate moderately broad at base, its width usually less than 3/4 width of 8th sternum, produced from 1/2 to 2/3 length of 9th sternum, broadly rounded posterior margin with variable mesoposterior emargination from broad and shallow to narrow and moderately deep (Figs. 111, 124); dark pigmentation variable, from covering entire plate to patterned, with most dark pigment anteriorly and laterally with posterior margin light; two variable, large, darker markings located anterolaterally on plate, usually connected to anterior segment by two thick, brown longitudinal bands.
Nymph.— General body color light brown with light and dark markings (Fig. 107). Head. Dorsum with contrasting pigment pattern; fine, short, clear, clothing setae sparse; light colored narrow band forming M-pattern between antennal bases and median ocellus; anterior transverse brown band variable, usually thick, completely enclosing M-pattern anteriorly, becoming light brown or speckled with small yellow blotches along anterior margin; anterior margin usually with narrow, transverse light band, brown area below enclosing M-pattern without two light areas; two small, irregular-shaped dark markings on anterolateral margins between antennal bases and labrum, sometimes faded; labrum with two, small, semicircular dark markings along anterior margin. Interocular area brown, similar to adjacent areas; post ocular and occipital spinule rows thin with many peg-like spinulae, usually with one longer spine in occipital row near post ocular row junction, another at mesal end of occipital row. Left and right mandibles under high magnification with ventral basal margin of distal-most cusp with short, indistinct row of small, vestigial denticles sometimes reaching beyond 1/2 length of cusp of one or both mandibles (Fig. 8). Thorax. Pronotum covered with densely scattered, short, thin, clear clothing setae. Abdomen. Abdominal terga with distinct, dark, anterior and posterior, transverse bands on segments 2–9, segment one with posterior transverse band thin, often faded in preserved material; segment 10 with dark pigment variable, sometimes with a pair of median yellow transverse bands with some dark pigment near posterior margin; short, clear, clothing setae sparsely interspersed between stout spines. Posterior setal row of male 8th abdominal sternum usually not mesally interrupted or with short interruption in mature nymphs.

Isogenoides varians (Walsh)

Male.— Macropterous. Length of forewings 13–15 mm; length of body 15–17 mm. General body color brown to dark brown and black. Head. Dorsum of head with variable, tiny, light area along mesoanterior margin (Fig. 133); large yellow area with base along posterior margin of head, anterolateral borders angled posteriorly, sometimes pointed, where broadly rounded mesoanterior border extends almost to epicranial suture intersection. M-pattern raised, without setae, dark brown throughout most of pattern, pattern not fading or blending into light anterolateral areas of frons, distolateral-most, posteriorly directed legs intercept lateral wrinkled areas along inner margins of antennal bases (Fig. 133). Interocellar area generally medium brown with dark brown pigment entering laterally, dark brown areas connect lateral ocelli to anterior ocellus, extending directly to large, lateral, medium brown rugosities; dark brown areas form two short, posterolaterally directed bands (Fig. 133). Thorax. Pronotal median longitudinal yellow stripe with small amounts of variable pigment along dorsal suture, generally stripe widest posteriorly, tapered slightly anteriorly to anterior margin of anterior transverse furrow, then expanded laterally above furrow (Fig. 133). Abdomen. Dark brown without thin dark brown to black transverse stripes along anterior margins; first tergum with variable-shaped unpigmented areas, hemitergal and subanal lobes yellow in dorsal view, contrasting sharply with darker cerci; dorsum entirely covered with dense, short, clear to light brown, clothing setae, longer at mesoposterior areas of terga 8–9, those on 8 longest; dorsolateral humps small, restricted to terga 8–9, visible in dorsal view, posterolateral areas slightly swollen dorsally, not laterally or posteriorly, swollen areas of 8th tergite largest; 9th tergite with variable transverse light area; wide transverse patches of partially erect clothing setae cover dorsal areas of humps (Figs. 127, 128). Hemitergal lobes in dorsal view with lobe apices directed posteriorly, not medially or anteriorly, apical margins narrowly rounded to slightly pointed, connected anteriorly by tiny, thin, laterally extended membranous area to mesoanterior wing-like internal basal anchor sclerites (Fig. 128); 14–20 wide, mostly short, golden brown, stout spinulae (sensilla basiconica) concentrated along mesoanterior margins of sclerites (Figs. 127, 128); short, dark, erect setae scattered over entire posterior portion of lobe, these interspersed within long, numerous, golden, hair-like setae covering entire posterior areas; 10th sternite with small variable dark pattern. Epiproct apex modified in lateral view with deep, internally sclerotized groove, not a hook (Figs. 129, 140, 141); posterior margin with heavily sclerotized pair of long, basally broad, posteriorly directed hooks, their position from apex about 1/5 to 1/6 total epiproct length in lateral view; in lateral view, under high magnification, anterior portion of epiproct with long, apically curved or slightly expanded, bluntly tipped, scale-like setae, lateral margins with deep, angled serrations (Fig. 142); anterior support sclerite trifid in anterior view, lateral arms stout, longer than base (Fig. 131), in lateral view curved anteriorly at apex with apical, anterior expansions forming thin, hook-like processes (Figs. 129, 140, 141), median arm separated from lateral arms basally, its apically pointed dorsal portion as long as base, ending before 1/2 length of entire epiproct (Fig. 131); posterior support sclerite single, stout, wide, lateral margins approximately parallel, with irregular-shaped hole near base below membranous epiproct portion, lateral margins expanding sharply to join laterally at slightly more than 3/4 total epiproct length from base, to pair of stout, heavily sclerotized, inwardly and posteriorly directed hooks, support sclerite continuing dorsally, margins parallel then tapering sharply, connecting to broad, apical, sclerotized groove (Fig. 130); Internal basal anchor in anterior view with narrowly expanded base tapering gradually to where anterior keel-like sclerite connects, expanding gradually into broadly triangular lateral plates (Fig. 132); long, wide, slightly curved, dorsal wing-like triangular sclerites directed dorsally from centrally located wide notch. Lateral stylets in lateral view with long, wide base (Fig. 129); expanded areas narrowly rounded at slightly more than 1/2 total length from base, apical 1/2 narrow at expanded region, margins approximately parallel, curving slightly to broadly rounded tips; in anterior or posterior view, stylets appearing about as wide as in lateral view (Figs. 130, 143); apical portions smoothly curved, apices directed slightly laterally. Aedeagus membranous with pair of distinct lateral lobes at dorsolateral apical margins (Figs. 135, 136); tiny, clear, erect setae sparsely scattered over entire surface of lateral lobes; two wide lobes dorsally, set between, slightly below, lateral lobes (Fig. 135); two plate-like lobes ventrally, immediately below lateral lobes (Figs. 1A, 127), may not be fully everted in some specimens, their inverted bases only visible (Fig. 136), dorsal apex sometimes bearing globular, fixed extruded semen appearing as additional lobes (Figs. 1A, 127); one low, moderately projected rounded knob, located mesally and apically as seen in dorsal view.
Female.— Macropterous. Length of forewings 16–18 mm; length of body 17–20 mm. General body color and head-pronotal pigmentation patterns similar to male. Subgenital plate broad at base, its width usually greater than 3/4 width of 8th sternum, produced from 3/4 to entire length of 9th sternum; broadly rounded posterior margin with variable mesoposterior characters (Figs. 134, 144): 1. mesoposterior margin of subgenital plate with short, almost vestigial, wide protrusion, 2. mesoposterior margin of subgenital plate with short, almost vestigial, narrow to wide, emarginated protrusion, 3. posterior margin of subgenital plate entire; dark pigmentation variable, from covering entire plate to patterned, sometimes with two, small, rounded light markings on plate, below mesally angled, posterior margins of abdomen, these markings enclosed by dark pigment posteriorly, connected to two, wide, light brown to yellow, longitudinal bands on anterior portion of segment.
Nymph.— General body color yellow with light and dark markings, yellow fading to cream when preserved (Fig. 126). Head. Dorsum of head with contrasting dark pigment pattern when live or recently preserved, becoming faded over time to light tan patterns mostly on posterior half; long dark clothing setae scattered mostly over pigmented areas; light colored narrow band forming M-pattern between antennal bases and median ocellus partially enclosed with dark pigment, its margins indicated by presence of long, dark moderately scattered, clothing setae enclosing pattern; anterior transverse brown band reduced, narrow, following contour of anterior M-pattern margin, usually faded on preserved specimens; anterior margin largely yellow to unpigmented, 4 small, irregular shaped dark markings mesoanteriorly between antennal bases and labrum, brown band below without two light areas; one pair located mesally above anterior-most portions of M-pattern, all mostly faded in preserved material; labrum usually yellow to unpigmented, covered with long, dark clothing setae. Interocular area brown, partially faded when preserved; post ocular and occipital spinule rows thin with many peg-like spinulae, usually with one longer spine in occipital row near post ocular row junction. Left and right mandibles under high magnification with ventral basal margin of distal-most cusp with long, distinct row of large denticles usually extending beyond 1/2 length of cusp of one or both mandibles (Fig. 9). Thorax. Pronotum covered with long, moderately dense, dark clothing setae. Abdomen. Abdominal terga with distinct, dark, anterior, transverse bands on segments 1–10, first and 10th segments with bands completely faded after 7-months in 75% EtOH; long, dark, clothing setae sparsely interspersed between stout spines. Posterior setal row of male 8th abdominal sternum variable, from not mesally interrupted to short interruption in mature nymphs.

References

Sandberg JB, Stewart KW. 2005. Holomorphology and Systematics of the Stonefly Genus Isogenoides (Plecoptera: Perlodidae). Transactions of the American Entomological Society 131(3+4): 269-345.