Isoperla arcana, Beaty & Holland & Lenat, 2017

Beaty, Steven R., Holland, Victor B. & Lenat, David R., 2017, Isoperla Arcana And Isoperla Borisi (Plecoptera: Perlodidae), Two New Stonefly Species From North Carolina, U. S. A. With Notes On The Distribution Of Isoperla Powhatan, Illiesia 13 (14), pp. 140-166 : 143-152

publication ID 10.5281/zenodo.4752853

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scientific name

Isoperla arcana

sp. nov.

Isoperla arcana View in CoL sp. nov. Plecoptera TaxonName:501179

Secret Stripetail

( Figs. 2–19 View Figs View Figs View Figs View Figs View Fig )

Material examined. USA – Holotype ♂ and larval exuvium, NORTH CAROLINA, McDowell Co., Curtis Creek, Curtis Creek Rd , 35.71459, -82.19079, 28/IV/2016, S.R. Beaty, V.B. Holland, E.D. Fleek ( NMNH) GoogleMaps . Paratypes: Alleghany Co., unnamed tributary to Little River, SR 1418, 36.5348, -81.1065, 15/ V /2013, S. R. Beaty, V. B. Holland, 6♀ (reared) and exuvia ( NCDWR). GoogleMaps Avery Co., Elk Hollow Branch, off Roaring Creek Rd. , 36.09947, -82.04547, 7/ V /2014, V.B. Holland, E.D. Fleek, M.D. Walters, 1♂ (reared) and exuvium, 3♀ (reared) and exuvia, 1 larva ( NCDWR); GoogleMaps Little Wilson Creek, Edgemont Rd. , 36.08316, -81.79131, 28/IV/2016, S. R. Beaty, V. B. Holland, E.D. Fleek, 1♂ (reared), 2♀ (reared) and exuvia ( NCDWR); GoogleMaps North Harper Creek , FSR 58, 36.00861, -81.85361, 9/ V /2016, S. R. Beaty, V. B. Holland, E.D. Fleek, 1♂ (reared) and exuvium ( NCDWR); GoogleMaps Wilson Creek , US 221 , 36.09694, -81.80777, 9/ V /2016, S. R. Beaty, V. B. Holland, E.D. Fleek, 1♂ (reared) and exuvium ( NCDWR). GoogleMaps Burke Co., Gingercake Creek , FSR 496, 35.92398, -81.87231, V.B. Holland, E.D. Fleek, M.D. Walters, 1♂ (reared) and exuvium ( CSUIC). GoogleMaps Buncombe Co., Coles Cove Branch , off SR 2132, 35.73569, -82.49934, 8/ V /2012, S. R. Beaty, M.D. Walters, D. Black, 2♀ (reared) and exuvia ( NCDWR). GoogleMaps Haywood Co., unnamed tributary to Raccoon Creek , off Pippin Lane, coordinates unknown, 8/ V /2012, S. R. Beaty, M.D. Walters, D. Black, 1♂ (reared) ( NCDWR). GoogleMaps Macon Co., Robin Branch, Wayah Rd. , 35.15498, -83.59143, 16/ V /2014, S. R. Beaty, V. B. Holland, E.D. Fleek, 1♂ (reared) and exuvium ( NCDWR). GoogleMaps Madison Co., Wolf Laurel Branch, off Oakridge Lane , 35.96783, -82.50488, 8/ V /2012, S. R. Beaty, M.D. Walters, D. Black, 1♂ (reared) and exuvium, 1♀ (reared) and exuvium, 1 larva ( NCDWR). GoogleMaps McDowell Co., Curtis Creek, Curtis Creek Rd, 35.71459, -82.19079, 28/IV/2016, S. R. Beaty, V.B. Holland, E.D. Fleek, 2♂ (reared) and exuvia, 1♀ (reared) and exuvium, 3 larvae ( NMNH); GoogleMaps 2♀ (reared) and exuvia ( CSUIC); GoogleMaps 7♂ (reared) and exuvia, 2♀ (reared) and exuvia, 2 larvae ( NCDWR). GoogleMaps Transylvania Co., Cherryfield Creek , off Still Waters Lane, 35.18460, -82.81165, 12/ V /2013, S. R. Beaty, T. Morman, M.D. Walters, 1♀ (reared) and exuvium, 2 larvae ( NCDWR). GoogleMaps Watauga Co., Boone Fork , Blue Ridge Parkway, 36.11904, -81.78168, 7/ V /2014, V.B. Holland, E.D. Fleek, M.D. Walters, 1♂ (reared) and exuvium, 1♀ (reared) and exuvium ( CSUIC); GoogleMaps Buckeye Creek , near Smoketree Rd., 36.20194, -81.89583, 9/ V /2016, V.B. Holland, E.D. Fleek, M.D. Walters, 1♀ (reared) and exuvium ( NCDWR). GoogleMaps Wilkes Co., Garden Creek , SR 1379, 36.39027, -81.07111, 8/ V /2014, V.B. Holland, E.D. Fleek, M.D. Walters, 1♂ (reared) and exuvium ( NCDWR) GoogleMaps .

Additional material: NORTH CAROLINA, Avery Co., Elk Hollow Branch , off Roaring Creek Rd., 36.09947, -82.04547, 7/ V /2014, V.B. Holland, E.D. Fleek, M.D. Walters, 11 larvae ( NCDWR); GoogleMaps Gragg GoogleMaps Prong , FSR 261, 36.03091, -81.80307, 6/ V /2014, V.B. Holland, E.D. Fleek, M.D. Walters, 2♀ (reared) and exuvia, 1 larva ( NCDWR); GoogleMaps Wilson Creek , Blue Ridge Parkway, 36.10084, -81.80778, 28/IV/2016; US 221, 9/ V /2016, S. R. Beaty, V.B. Holland, E.D. Fleek, 3 larvae ( NCDWR). GoogleMaps Buncombe Co., North Fork Swannanoa River , upstream Burnett Reservoir, 35.70414, -82.32984, 6/ V /2014, V.B. Holland, E.D. Fleek, M.D. Walters, 3 larvae ( NCDWR). GoogleMaps Caldwell Co., Thorp Creek , NC 90, 35.9953, -81.7604, 12/IV/2012, S. R. Beaty, V.B. Holland, E.D. Fleek, 3 larvae ( NCDWR). GoogleMaps Clay Co., Fires Creek , FSR C, 35.14027, -83.75638, 19/IV/1988, L.E. Eaton, D. Penrose, C. Smith, 1 larva ( NCDWR). GoogleMaps Jackson Co. , small seep, off Cold Mountain Rd., coordinates unknown, 1/III/2006, D. R. Lenat, 3 larvae ( NCDWR). GoogleMaps Macon Co., North Fork Coweeta Creek , SR 1114, 35.06525, -83.40253, 17/ V /2011, V.B. Holland, T. Morman, M.D. Walters, 3 larvae ( NCDWR). GoogleMaps Madison Co., Big Creek, Big Creek Rd., 36.02388, -82.65333, 5/IV/2015, S. R. Beaty, V.B. Holland, E.D. Fleek, 1 larva ( NCDWR). GoogleMaps McDowell Co., Cow Creek , SR 1443, 35.79666, -82.12166, 20/IV/2005, W.B. Crouch, E.D. Fleek, M.D. Walters, 7 larvae ( NCDWR); GoogleMaps Reedy Branch , NC 80, 35.73277, -82.01779, 21/IV/2005, W.B. Crouch, B. Prusha, M.D. Walters, 4 larvae ( NCDWR); GoogleMaps unnamed tributary to Peppers Creek , Peppers Creek Rd., 35.87586, -82.01779, S. R. Beaty, E.D. Fleek, B.C Kondratieff, C.J. Verdone, 1♀ (reared) and exuvium ( NCDWR). GoogleMaps Transylvania Co., Cove Branch , FSR 225, 35.30310, -82.82783, V.B. Holland, E.D. Fleek, M.D. Walters, 10 larvae ( NCDWR) GoogleMaps .

Distribution. USA – NC.

Adult Male — Macropterous. Forewing length 9.0– 10.0 mm (n=12), body length 7.5–8.5 (n=14). General pattern on head dark and bell or hatshaped with a brown U-shaped to triangular spot on anterior edge of head. General body color pale yellow in life with some brown markings.

Head: Palpi pale yellow-brown. Labrum with stiff, short setae. Dorsum of head ( Fig. 2 View Figs ) mostly pale cream with variable dark brown quadrate pattern connecting median ocellus with lateral ocelli and covering interocellar area; interocellar area may be paler posteriorly between the lateral ocelli on some individuals thus appearing as simple dark bands extending from the median ocellus to each lateral ocellus; usually with a Ushaped to triangular brown area on frons separated from median ocellus by pale yellow-brown line; frontoclypeus pale anterolaterally and anterior to eyes; occiput completely pale white to pale yellow; tentorial callosities indistinct; short, dark setae restricted to interocellar area, some setae visible just anterior to lateral ocelli. Antennal scape and pedicel pale yellow-brown tending darker towards apex of each segment; flagellum brown with basal few segments lighter than remainder, antennal length about ¾ length of body with 33–36 segments.

Thorax: Pronotum with wide, pale median stripe ( Fig. 2 View Figs ); pronotal margin anterior to furrow dark brown, sometimes narrowly interrupted medially; posterior edge of pronotum barely margined with brown, if at all, and delineated only by a row of thick, dark, short setae along edge; lateral pronotal margins pale white; mid-dorsal pronotal suture with thin brown line; pronotal disks yellow-brown with most rugosities brown, edged with darker brown, some yellow-brown; rugosities coalesced medially, more distant laterally, raised; short, dark setae anterior and posterior to pronotal sclerites, pronotal disks with short dark setae restricted to rugosities and areas in-between, setae absent from medial pale stripe and lateral edges of disks. Meso- and metanota yellow-brown with brown scutal humps ( Fig. 6 View Figs ), pale yellow-brown stripe medially, anterior areas of nota pale; nota covered entirely with short, dark setae. Wings smoky hyaline with light brown veins. Meso- and metabasisterna mostly pale yellow; furcal sternites pale white.

Legs: Pale overall. Anterior and posterior faces of femora pale white, narrowly yellow-brown dorsally, dark brown at extreme apical margin; tibiae pale to yellow-brown with thin dark brown band near basal fourth and slightly darker apically; tarsi brown, segment 3 darker apically; claws and arolia darkened dorsally; leg vestiture dense with short dark setae giving legs a darker overall appearance; tibiae with a subdorsal and ventral row of larger spines.

Abdomen: Overall pale white to yellow-brown with a longitudinal brown median dorsal stripe. Terga 2–9 pale yellow to yellow-brown, each tergum with a medial brown patch, contiguous with successive segments and thus appearing as a longitudinal brown stripe, becoming indistinct to absent on posterior segments; brown medial patch on anterior segments subtriangular, wider posteriorly; each tergum with a dense patch of long silky clear setae laterally and shorter darker setae along posterior half to two-thirds on each segment; tergum 9 and 10 yellow-brown, paler laterally; 9 with a medially interrupted, transverse brown line at anterior edge of segment and with a setose, brown posteromedial protuberance; setae and spinule patches on 10 absent from shallow medial furrow ( Fig. 3 View Figs ). Paraproct length short, subtriangular in dorsal view, apices bluntly pointed and with outer surface lightly sclerotized and light brown; dorsum of paraprocts slightly rugose and with setae; paraprocts curved upwards and medially, barely recurved over the apex of tergum 10. Anterior sterna pale white but gradually changing to pale yellow-brown at abdominal apex; sterna 2–5 mostly glabrous, setae become more numerous on each successive posterior segment. Sternum 8 with posterior edge slightly darkened and with a row of brown brushlike setae, with a pale brown vesicle about 1.4X wider than long; posterior edge of vesicle darker, evenly rounded to subtruncate, extending to or barely over base of segment 9 ( Figs. 4 View Figs , 13 View Figs ), the distal third of vesicle glabrous but with marginal hairs. Cerci pale yellow gradually darkening to pale yellow brown, last segment darkened distally, cercal length ½–⅔ as long as abdomen, with 11–14 segments, each segment with one long, colorless ventral seta near posterior margin, basal 4–6 segments with dorsal and ventral tufts of long stiff setae, setae becoming shorter and less numerous on each successive segment.

Aedeagus: Basal stalk encircled with a moderately dense band of short, sharp spinulae ( Figs. 5e View Figs , 15 View Figs ); a rectangular to quadrate median patch of golden spinules with apical finger-like projections ( Figs. 5d View Figs , 16, 17 View Figs ) above a glabrous posteroventral lobe ( Figs. 5a View Figs , 14a View Figs ), between paired posterolateral lobes ( Figs. 5b View Figs , 14b View Figs ), and below a transverse posterodorsal lobe which is invaginated supramedially ( Figs. 5c View Figs , 14c View Figs ); a large, mostly glabrous terminal dorsal lobe; a few sensillae basiconica scattered at base of the paired posterolateral lobes ( Fig. 18 View Figs ).

Adult Female — Macropterous. Forewing length 10.0–12.0 mm (n=18), body length 8.0–10.0 (n=18). General head pattern and body color similar to that of the male, although the dorsal abdominal stripe is less conspicuous and may be absent in lighter individuals ( Fig. 6 View Figs ).

Subgenital plate: generally acutely triangular, originating from the distal third of sternum 8 from near pleural folds and produced posteriorly approximately ¾ the length of sternum 9; plate basally broad, about ¾ the width of segment 8 on most specimens, apex pointed ( Fig. 7 View Figs ), plate with long and short setae on body; coloration of plate similar to remainder of segment 8.

Ovum — Unknown.

Mature Larva — Pre-emergent larvae 7.0–10.0 mm (n=19). Body moderately slender with contrasting body pattern ( Fig. 8 View Figs ). Clothing hairs present, dorsally dark, ventrally brown to clear.

Maxilla: Lacinia bidentate ( Fig. 9 View Figs ); receding evenly from base to subapical tooth; a thin, long marginal seta present between apical and subapical teeth; 5–7 striated stout marginal setae below subapical tooth, last few setae progressively smaller; first marginal seta below subapical tooth somewhat isolated, removed from remaining marginal setae ( Fig. 9a View Figs ); 8–14 thin, unevenlyspaced setae along palm edge and curving dorsad; a widely-set submarginal row of 3–5 striated stout setae from apical tooth ( Fig. 9b View Figs ); some specimens may have an occasional extra thin submarginal seta interrupting the submarginal row (not illustrated); uneven row of 5–10 thin setae on ventral surface near palm edge and approaching base of lacinia, setae near base short; dorsal setae few to absent. Length of striated apical tooth of lacinia between 0.5–0.6X palm length and 0.7–0.9X the palm width. Subapical tooth 0.5–0.6X the length of the apical tooth. Galea 1.0–1.1X the lacinial palm length, with a ventral row of more than 30 setae and tipped with 2–4 apical spinous setae. Maxillary palp setose, 1.3–1.6X length of lacinia; segments 1–3 successively longer, segments 3 and 4 subequal and slightly longer than 5; segments 1 and 2 with transverse row of apical spinous setae, segment 3 sometimes with 1 apical spine, segment 5 tipped with 1–2 sensillae.

Mandible: Left mandible bicuspid; outer cusp with 3 teeth, ventral tooth largest and serrated basally, dorsal tooth smallest; a band of unorganized, long spinous setae on ventral surface from base of teeth to base of mandible; inner cusp with 3 teeth, middle tooth longest and largest; a brush of dense short spinous setae basal to cusp near molar ridge; a series of spine-like setae along molar ridge, setae longer and thinner towards base of mandible; a band of unorganized and serrated setae on dorsal surface from base of inner cusp towards base of mandible, setae shorter and thinner towards base. Right mandible similar to left mandible except dense brush of setae at base of inner cusp replaced by a short patch of denticlelike acanthae.

Dorsum of head: head brown with distinctive pale M-pattern ( Fig. 10 View Figs ), pattern sometimes medially obfuscated; a pair of transversely oriented pale dashes anterior to M-pattern, sometimes obscure; a medial dark brown transverse band posterior to M-pattern encompassing median ocellus, usually darker than remainder of head and appearing somewhat like a mask, mask may be difficult to see in old preserved specimens or younger instars; ocellar spot obscure to absent, if present then small and faint; a pair of obliquely oriented pale mediolateral spots always present; occiput with brown areas along epicranial suture, pale with brown reticulated pattern behind enclosed posteriorly by a heavily spiculate curved dark bar from epicranial stem to eye; labrum pale, darker basally, anterior margin with long setae, medial bulge clothed with a short, brown pubescence. Entire head with dark clothing hairs. Antennae yellow-brown, darker apically; pedicel brown; scape slightly darker than basal flagellar segments.

Thoracic nota: Pronotum brown, medial stripe obscure ( Fig. 10 View Figs ); anterior pronotal flange brown, sometimes medially interrupted; lateral edges pale, with sublateral brown stripes to posterior margin, sometimes obliterated medially; pronotal disk with brown reticulated markings between irregular pale rugosities; posterior pronotal flanges brown; pronotum rimmed with short, closely set, stiff setae, an occasional long seta near posterolateral corners. Meso- and metanota with brown markings, with anterior areas dark brown ( Fig. 11 View Figs ); wing pads light brown with medial stripe obliterated posteriorly, often lacking strong patterning; edges of nota fringed with a short, closely set row of stiff setae. All thoracic nota densely covered with dark clothing hairs. Thoracic sterna pale, without distinctive markings.

Legs: Femora brown overall ( Fig. 8 View Figs ); ventral face mostly pale; anterior face light brown and densely covered with dark clothing hairs giving it an overall darker appearance, usually with a darker submedial longitudinal brown band; tibiae pale yellow-brown, proximal fourth slightly darker; femora and tibiae with a dorsal fringe of long silky setae; long spinous setae dense on dorsal surface of femora, spines regular but scattered along anterior and posterior faces; tibiae with two dorsal and two ventral longitudinal rows of short spines. Tarsi pale yellow-brown with a ventral row of stiff setae and a sparse dorsal row of silky setae.

Abdomen: Variable, brown overall with two conspicuous, longitudinal dark stripes ( Figs. 8, 12 View Figs ); stripes bordered by pale lines; each tergal portion of the lateral stripes usually wider anteriorly and barely reaching posterior edge of respective segment, maculations may be subtriangular on posterior segments but sometimes parallel and reaching posterior edge; stripes will appear contiguous if segments are partially retracted into each other; a faint pair of anteromedial dots on dorsum of each segment may be visible in some specimens; dorsum of abdomen with numerous socketed stout setae with dark origins; posterior edges of terga dark brown and bearing a transverse row of long clear spines; dark clothing hairs abundant on dorsal surface. Abdominal sterna pale, clothing hairs darker on posterior segments, lighter on anterior segments; stout, socketed setae with dark origins on posterior sterna, anterior sterna almost bare; posterior edges bearing a transverse row of long socketed spines, row incomplete medially on anterior segments. Cerci yellow-brown with sparse dorsal fringe of silky setae on distal half.

Etymology. The word arcanus refers to “hidden” or “secret” in Latin. The species epithet arcana was chosen to signify that the adult of this species remained unknown to science despite the larva being collected for over 30 years in routine water quality assessments.

Diagnosis. The habitus of the adult male I. arcana superficially resembles that of I. holochlora Klapálek, 1923 and other generally pale members of the I. signata group. The paraprocts of I. arcana are pointed rather than bluntly rounded as in I. holochlora . Also, differences in aedeagal armature will serve to separate I. arcana from other I. signata group species. The aedeagus is generally similar to that of I. powhatan , being mostly membranous and with a wide rectangular spinule patch. However, unlike the sharp spinules of I. powhatan , the patch on I. arcana is composed of scales with 2–6 apical finger-like projections ( Figs. 16, 17 View Figs ). Isoperla arcana also has a wide band of sharp spinule around the basal aedeagal stalk.

The subtriangular subgenital plate of female adults of I. arcana is similar to that of I. holochlora and I. dicala Frison, 1942 . Some variation has been observed in the overall width of the subgenital plate but it is typically shorter and not overlapping as much of segment 9 as in I. holochlora . Isoperla dicala does not possess a median dorsal abdominal stripe distinguishing it from females of I. arcana .

The combination of abdominal stripes, similar to those of I. holochlora larvae, and the dark head pattern with a distinct, but pale M-line, shared only by the few known larvae of the I. similis and I. pseudosimilis groups, will allow separation of I. arcana larvae from all other known eastern Nearctic larvae.

Type Locality. Curtis Creek ( Fig. 19 View Fig ) is a first to third order, high gradient tributary of the Catawba River in McDowell County, North Carolina. The watershed of Curtis Creek lies on the south side of the Blue Ridge Escarpment in the Southern Crystalline Ridges and Mountains Level IV ecoregion ( Griffith et al. 2002) and is contained almost entirely within the Pisgah National Forest. At the site of collection, about 5 km below the Blue Ridge Parkway (elevation 787 m), the stream is about 1–3 m wide and has a drainage area of approximately 2.1 km 2. In-stream habitat consists of bedrock slides, boulder and cobble cascades, and small areas of sand at the bottom of plunge pools and at stream edges. Well-conditioned leaf packs were abundant at the time of sampling as were several debris dams. While water quality at the type locality has never been assessed using North Carolina Biotic Index protocols ( NCBI; Lenat 1993, NCDEQ 2015), a larger, long term monitoring site approximately 6 km downstream on Curtis Creek has rated Excellent since 2007 with a macroinvertebrate community dominated by intolerant Ephemeroptera , Plecoptera , and Trichoptera (EPT) .

Curtis Creek is typical of minimally disturbed, high gradient headwater streams in the Appalachian Mountains. Macroinvertebrate species richness routinely exceeds 40 EPT taxa during the summer months when routine bioassessments are conducted, with even higher species richness during the spring months.

Additional Remarks. The North Carolina Division of Water Resources Biological Assessment Branch has over 150 verified larval records of Isoperla arcana (as I. nr. holochlora ) dating back to 1988. All of these records are from mountain streams ( Fig. 45 View Fig ) with a majority (82%) in streams with a drainage area of less than 13 km 2 (5 mi 2) and with 75% in streams of less than 5 m wide. There are no verified North Carolina records of this species occurring in streams over 100 km 2 or wider than 25 m. In addition, 91% of all I. arcana records occur from streams either rated Excellent or Good by North Carolina water quality assessment methods (NCDEQ 2015) indicating that this species is highly intolerant to disturbance. The pollution tolerance value assigned to I. arcana (as I. nr. holochlora ) and used in the NCBI is 0.0, the lowest value possible.

Little is known of the habitat or life history of I. arcana . Larvae are abundant in leaf packs but are readily collected from riffle habitat with little detrital substrate. Feeding habits are unknown, although carnivory seems likely at least in later instars as larger larval specimens have been collected with partially digested chironomid larvae. Adults emerge as early as mid-April in lower elevations to late-June in higher elevation streams. There are no previously published records of adults collected in the wild suggesting that they may be active in the stream canopy out of reach of typical collecting methods. A univoltine-slow life cycle is presumed for this species.


Smithsonian Institution, National Museum of Natural History


Royal British Columbia Museum - Herbarium


Departamento de Geologia, Universidad de Chile


Tavera, Department of Geology and Geophysics













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