CLADOENDESIS OF EPHEMEROPTERA

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(1) Maxilla is specialized as filtering (Kluge 2004: Fig.106:B–C): its apical margin is widened and truncate, with a large field of very densely and regularly situated long filtering setae; ventrad of this field, an apical-ventral row is developed – a short row of stout elongate pectinate setae, which are much shorter than filtering setae of the apical field; this apical-ventral row of pectinate setae reaches inner margin of maxilla but fare not reaches its outer margin. The apical-ventral row of pectinate setae can be either straight and integral, or curved, or divided into two parts  (Kluge et al. 2022: Fig.112–113). These elements (the field of filtering setae and the apical-ventral row of pectinate setae) occur also in some other mayfly groups, but not in such combination (see Index of characters [1.1.31] and [1.1.32]).

In connection with the filtering specialization, canines and dentisetae undergo reduction: if all 3 canines and 2 dentisetae are retained, they are diminished and brought together; in Atalophleboadentata canines are lost; in Atalophlebomaxillata distal dentiseta is also lost, and proximal dentiseta is pectinate and involved into apical setal crown. In a few Atalophlebomaxillata (e.g. Hermanellognatha, Choroterpides) this pectinate dentiseta is lost, the apical-ventral row of pectinate setae also can be vestigial or lost. In some independent taxa of Atalophlebomaxillata (e.g., Hermanellognatha, Hagenulus/fg3, Choroterpides) median-apical angle of maxilla is produced forming a tusk-like projection, which functionally substitutes the lost canines. In various Leptophlebia/fg1 mouth apparatus apart of maxillae either retains primitive biting structure, or gets more or less deep filtering specialization.

(1.1) Larval pronotum with humeral setae, located on antero-lateral sides of pronotum and directed  latero-posteriorly or laterally. These setae are arranged either irregularly, or form more or less regular row parallel to the free anterior margin (if it is expressed). In Hermanellognatha compact bunch of these setae is shifted backward [see below, Hermanellognatha (2)]

Non-unique apomorphies of Leptophlebia/fg1.

(2) Labrum initially with stout setae on distal margin. These setae are retained in pm.Leptophlebia/fg2, Calliarcys and Habrophlebia/fg1, but are lost in Atalophleboculata.

(3)(2) In imago and subimago left and right halves of mesonotal suture are curved posteriorly and stretch backward so strongly that medially they go along median longitudinal suture, and laterally – along lateroparapsidal sutures. In subimago mesonotal suture separates pigmented area from a light median stripe and a pair of light lateral stripes; lateral pigmented area of subimaginal mesonotal occupies lateroparapsidal suture up to its end, and all area laterad of it – sublateroscutum and lateroscutum; thus subimaginal mesonotal pigmentation has a characteristic pattern (Kluge 2004: Fig.106:D; Kluge 2013: Fig.51-53). Non-unique apomorphy: the same in Fimbriatotergaliae and Tetramerotarsata. In Leptophlebia/fg1-Hermanellonota mesonotal suture is disappeared completely, being fused with median longitudinal and lateroparapsidal sutures, and subimaginal mesonotum lost pigmentation (Kluge 1994b: Fig.13; 2004: Fig.106:E; Kluge 2008: Fig.29).

(4)(3) Imaginal and subimaginal furcasternal protuberances are separated, between them metathoracic nerve ganglion is situated. Non-unique apomorphy (see Index of characters [2.2.23]).

(5) On fore wing fork of MA is initially asymmetrical: either MA₂ arises under larger angle than MA₁, or point of furcation is shifted posteriorly. In certain taxa furcation of MA secondarily becomes symmetrical (see Index of characters [2.2.43]).

(6)(4) On fore wing CuP in its extreme base strongly diverges from CuA and close to base is strongly curved, thus outstanding from CuA (Kluge 2004: Fig. 106:F). The transverse portion of CuP base can disappear, in this case base of CuP appears to be widely separated from the base of CuA. Non-unique apomorphy; the same in Tetramerotarsata only.

(7)(5) Cubital field of fore wing [see Anteritorna (1)] usually with 2 intercalaries (Kluge 2004: Fig.106:F) or one bifurcate vein arising from CuA and/or CuP. Non-unique apomorphy (see Index of characters [2.2.51]). Sometimes number of intercalaries is increased.

(8) Larval fore, middle and hind legs are differentiated. Fore femur is widened near base (where tibial adductor is attached), with outer margin convex basally; usually for femur is widest near base, while other femora are widest near middle or in distal part (Kluge 2012: Fig.24-27, 147-149; Kluge 2013: Fig.29-31). Usually setation on fore, middle and hind legs differs as the following: Fore tibia [which always lacks patella-tibial suture – see Variable characters] has dense stout pointed setae on inner margin (while other tibiae usually have less dense stout pointed setae on inner margin). Hind tibia has a sparse row of long stout setae on outer margin (while other tibiae usually have no stout setae on outer margin). Middle leg usually has no these features, but in some taxa middle leg repeats shape and/or setation of fore or hind leg. Besides stout setae, outer margin of femur, tibia and tarsus of all legs usually bear long thin hair-like projected setae. In some taxa these or that of these features disappear or appear on all legs.

(9)(6) Larval claw usually with one row of denticles on inner side (non-unique apomorphy – see Index of characters [1.2.21]); rarely denticles are secondarily lost, or form two rows, or in addition to the main row several subapical denticles are present. One longitudinal row can be more or less distinctly subdivided into a distal row (located on main portion of claw) and proximal row (located on articulatory portion of claw) (Kluge 2012: Fig.95).

(10)(7) Tergalii lack costal and anal ribs or their vestiges [see Furcatergaliae (5)]. 

Probably the initial shape of tergalius is either bifurcate, or bilamellate; each of two branches (or lamellae) are slender, with stretched pointed apex (costal branch of bifurcate tergalius corresponds to dorsal lamella of bilamellate tergalius, and anal branch corresponds to ventral lamella). Tergalii of such two types and types intermediate between them are present in majority of Leptophlebia/fg1.

Besides this, tergalii of various other forms are found: tergalii can be unilamellate (when anal branch, or ventral lamella, is lost); both or one lamella can have margins smooth or with numerous processes; several times independently evolved such bilamellate tergalii where each lamella has three apical processes, middle of which represents the initial pointed apex (Kluge 2012: Fig.77-82, 99-105). Ability of rhythmical respiratory movements is usually retained, in exceptional cases lost (see Index of characters [1.3.30]). Some taxa (Australian Kirrara, New Zealand Deleatidium and New Caledonian Lepeorus and Lepegenia) have strongly modified lamellate tergalii, which form a sucking disk similar to that of Rhithrogena/fg3 and Iron/g1; such tergalii can have secondary ribs reminding primary ribs of other mayflies. Adenophlebiodes has tergalii I transformed to gill opercula. Usually all tergalii I-VII are present, but in some taxa tergalius I or VII are lost.

Plesiomorphies of Leptophlebia/fg1. In larva: Maxillary palp is always 3-segmented. Labial palp is always 3-segmented.

Paracercus is always multisegmented, usually subequal to cerci [only in Blasturus (in Leptophlebia/fg4) markedly smaller].

In imago and subimago: Gonostylus nearly always retain 2 distal segments (reduced to one distal segment in a few non-related species). Paracercus is nearly always well-developed, usually subequal to cerci (diminished only if diminished in larva – see above).

Variable characters of Leptophlebia/fg1. In larva: Patella-tibial suture can be normally developed on middle and hind legs (in Leptophlebia/fg2 and some Atalophleboadentata), or lost on middle legs (in Habrophlebia/fg1 and some Atalophlebolinguata), or lost on all legs (in some Atalophlebolinguata). Abdominal terga are usually smooth, rarely with median projections. Usually all tergalii [see (7)] have normal dorsal attachment on posterior margins of segments, but in Isca tergalial bases are transferred ventrally.

In imago and subimago: In most representatives molt from subimago to imago takes place in both sexes, but in selected taxa females do not molt. Male eyes have usual for mayflies division to dorsal and ventral portions; in selected taxa the dorsal portion is transformed to turban eye (like in Turbanoculata); in Fulleta/g1 (incl. Fulletomimus) division to dorsal and ventral portions is lost. Imaginal wings usually have no setae, but sometimes marginal setae are present, like in subimago. Hind wing can be either well-developed (as long as 0.25–0.35 of fore wing lenght), or diminished, or lost; if developed, Sc can reach wing apex or terminates much more proximally; costal margin can be smooth or with prominent projection just proximad of Sc apex; triads of RS and MP [see Furcatergaliae (4)] can be either developed, or MP is unbranched. Claws can be either ephemeropteroid, or both pointed (see Index of characters [2.2.85]); claws of male fore leg can have the same structure as others (ephemeropteroid or pointed), or both are blunt.