CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Turbanoculata.

(1) In male imago dorsal part of each eye is transformed to a turban eye: it has cylindrical stem lacking facets (only vestiges of ommatidia with pigmented cells can be retained on stem), thus faceted surface of turban eye is separated from faceted surface of ventral eye portion (Zimmer 1897: Fig.1-13; ). In subimago turban eye has stem less expressed than in imago (); in larva stem is completely absent and a turban eye bud has a form of flat spot distinctly separated from lower portion of eye. Exception is made by Aturbina, where turban eyes are secondarily reduced, thus male eyes become small and simple as in female. Besides Turbanoculata, similar turban eyes are present in some Leptophlebia/fg1.

(2) Imaginal and subimaginal furcasternal protuberances are separated, between them metathoracic nerve ganglion is situated (Kluge 2004: Fig.29:A); if furcasternal protuberances are connected, metathoracic ganglion is situated anteriad of the point of their connection. Non-unique apomorphy (see Index of characters [2.2.23]).

Characters of Turbanoculata of unclear phylogenetic status: it is unclear if these characters are autapomorphies of Turbanoculata or Liberevenata, because for Palaeocloeon they are unknown.

(3) Larval paired frontal sutures – i.e. anterior arms of Y-shaped epicranial suture, by which cuticle is broken at moult – pass anteriad (ventrad) of lateral ocelli or close to anterior (ventral) margins of these ocelli, thus separating the lateral ocelli from median ocellus (Wang & McCafferty 1996b: Fig.1-6). Unique apomorphy: in other Ephemeroptera the frontal suture is connected with lateral ocellus in middle or posterior part of the ocellus (ibid.: Fig.7-12).

(4) Labrum has a distinctly expressed median incision; row of branching setae near distal margin [see Tetramerotarsata (6)] is regular all over its length. In cases of strong specialization of labrum (in predators) these details can disappear (see Index of characters [1.1.16]). Long setae on dorsal surface of labrum are often regular, forming one submedial pair and pair of transverse rows near anterior-lateral angles; in some taxa arrangement of these setae is different or disordered.

(5) Kinetodontium is immobile fused with mandible and more or less fused with incisor (Kluge 2004: Fig.29:B). Non-unique apomorphy.

(6) Prostheca of left mandible is elongate in a form of stout integral stick, only apically is divided into several short projections (Kluge 2004: Fig.29:B) (unlike brush-like prostheca of other mayflies). Probably, initial for left prostheca is the «Baetis-type»: wide, terminated by 3–6 blunt more distal denticles and 2–4 pointed more proximal denticles; all denticles of incisor, kinetodontiom, prostheca and mola are visible in one view (Kluge 2004: fig. 29B). In some non-related taxa mandibles have modified structure of the «Centroptilum-type», when kinetodontium is separated from incisor (but remains to be immovable) and rotated perpendicular to the plane of mandible, so that its denticles hide one another in dorsal or ventral view; in this case left prostheca is bifurcate and rotated in the same manner as kinetodontium (Kluge & Novikova 2017: Fig.13–14, 38–39, 61–62) (see Index of characters [1.1.22], [1.1.24]).

Prostheca of right mandible either has similar structure, or is vestigial, sometimes setiform or in a form of bifurcate seta . On inner margin of mandible proximad of prostheca, irregularly situated setae can be present (non unique character). Probably presence of these setae is initial for Turbanoculata, as they are present in such primitive groups as Protopatellata, Cloeon/fg1 and others. In selected groups inside Turbanoculata (particularly, in all Baetofemorata) these setae are completely lost.

(7) Glossae and paraglossae have peculiar structure: bases of glossae are widened ventrad of bases of paraglossae; in their most part glossae are narrow, in their middle part are situated between paraglossae, and in distal part can be projected somewhat dorsad of paraglossae; paraglossae arise from mentum apically (not laterally) and beginning from their bases have lateral margins usually parallel-sided or convergent distally (Kluge 2004: Fig.28:C). Unique apomorphy; in Nesameletus/f1=Metamonius/g1 glossae and paraglossae are similarly parallel-sided, but bases of glossae are not widened, and paraglossae retain lateral attachment. In most Turbanoculata glossae are slightly shorter than paraglossae and in their distal part narrower than paraglossae; in some taxa glossae are diminished, being much shorter and/or narrower than paraglossae.

(8) Unlike Siphlaenigma, adult mesonotal relief is not expressed in larva (as in majority of Ephemeroptera); larval fore protoptera are fused with scutellum nearly up to apex of scutellum, so that free portion of each protopteron narrows from its extreme base toward apex (Kluge 2004: Fig.28:A). Non-unique apomorphy (see Index of characters [1.2.6]). Usually fore protoptera are separated beginning from the apex of scutellum, but in Pseudopannota/g2 they are fused one with another behind scutellum.

(9) Subimaginal sclerites of lateral mesothoracic wall have unique structure (Kluge 2004: Fig.29:A): Sclerite of lateropostnotal crest is long and straight; the sclerite of metathoracic katepimeron is distinct, long, narrow, stretches posteriorly up to ventral end of the sclerite of lateropostnotal crest. Paired transverse postnotal sclerite, which unites mediopostnotum with posterior-dorsal angle of postsubalar sclerite, is immobile fused with postsubalar sclerite and looks as a its process.

(10) Hind wings are diminished, usually as long as 0.2 of for wing length or shorter (rarely longer), narrowed, in many representatives lost; venation of hind wing is strongly reduced: there are no furcations of RS, MA and MP, no veins behind MP; usually only Sc and RA are present, sometimes also non-branched MP; instead of RS and MA one or several intercalaries can be present, sometimes a single vein (probably MA) arises from RA. Non-unique apomorphy (see Index of characters [2.2.59]). Structure of hind wing of Palaeocloeon is not quite clear; probably some of these characters belong to Liberevenata in general.

Possibly, the most primitive for Turbanoculata is hind wing of "Centroptilum-type": narrow, with non-branched longitudinal veins and with long costal projection, which is situated in proximal part of wing, projected anteriorly and curved in distal direction: such form is present in species formerly placed to the artificial genus Centroptilum sensu Eaton 1883-1888, and recently placed to Protopatellata, Cloeon/fg1 and some other taxa. In selected groups of Turbanoculata other forms of hind wing are present: wing of "Baetis-type" is wider, with shorter non-curved costal projection; "Nigrobaetis-type" has the same shape, but the second vein is bifurcate. Sometimes costal projection is lost. In many groups of Turbanoculata hind wings disappear completely, in many cases disappearance of hind wings takes place in selected species and can not be regarded as a character of supra-species taxon; formerly species without hind wings constituted artificial genera Cloeon sensu Leach 1815 and Pseudocloeon sensu Klapalek 1905; recently first of them are placed to Protopatellata and Anteropatellata-non-Baetovectata, and the second ones – to Baetovectata. In most cases size and structure of hind wing (or its absence) is the same in both sexes, but in a few species hind wings are present in male and lost in female, or are larger in male and smaller in female.

(11) On apex of larval femur the anterior-outer projection [i.e. projection situated on anterior (dorsal) side of femur outward from incision, into which the anterior articulating condylus of tibia is inputted] is curved toward inner side of femur; it can be from small and slightly curved to very large, rounding the anterior tibial condylus from distal side and overlapping on anterior-inner apical femoral projection (Wang & McCafferty 1996b: Fig.13-16). Unique apomorphy.

(12) Larval abdominal tergal surfaces and other parts of body usually bear small (about 0.01 mm) translucent scales situated in wide semilunar sockets. Probably initial form of these sockets is angulate with a pair of covers at the corners (Kluge 2004: Fig.29:C) – such form occurs in some Protopatellata and some Anteropatellata. In other cases sockets have rounded form without covers. In some Turbanoculata scales are lost. In other mayflies such scales never occur. Siphlaenigma has no scales. It is unclear if presence of scales is autapomorphy of Turbanoculata or Tetramerotarsata, because their absence in the single species of Siphlaenigma may be either initial, or a result of reduction.

(13) Larval protogonostyli and protopenis are strongly diminished, sometimes lost, thus shape of posterior margin of larval abdominal sternum IX in male is nearly the same as in female (unlike majority of other Ephemeroptera); only in Callibaetis and a few other taxa protogonostyli are distinctly projected (probably being enlarged secondarily). In connection with reduction of larval protogonostyli, subimaginal gonostyli buds, which develop in larva, are folded under larval cuticle in a special manner. Probably the initial is "Afroptilum-Cloeon-type", when 2^nd segment of gonostylus is directed laterally as a whole; 3^rd [distalmost – see Liberevenata (5)] segment can be curved medially ("Cloeon-type") (Kluge 2004: Fig.29:F) or also directed laterally ("Afroptilum-type") (Kluge 2004: Fig.29:D-E); such position occurs in Protopatellata, and among Anteropatellata is present in all Cloeon/fg1, Baetopus/fg1, Cheleocloeon and Afrobaetodes; judging by shape of gonostyli in subimago, the same position was peculiar for Palaeocloeon (Kluge 1997c: Fig.15). In Baetovectata position of subimaginal gonostyli under larval cuticle is different: 2^nd segment can be directed posteriorly ("Nigrobaetis-type"), or medio-posteriorly ("Baetis-type"), or curved medio-anteriorly ("Labiobaetis-type" and "Acentrella-type") (Kluge 2004: Fig.29:G-I) [see below, Baetovectata (3)].

(14) Malpighian tubes are straight, each tube lies along gut by its free end directed posteriorly; its duct arises from anterior end posteriorly, under acute angle (Landa 1969b: Fig.12:BR) (unlike majority of mayflies, where Malpighian tubes are coiled and situated irregularly). Non-unique apomorphy.

(15) Ganglion of abdominal segment VIII is approximated to that of segment VII. Non-unique apomorphy.

Variable characters of Turbanoculata. Larvae of most species have primitive siphlonuroid structure (Kluge 2004:Fig.28:A); only in selected taxa these or that modifications appear.

Larval head is hypognathous and usually elongate dorsoventrally (as in Siphlonurus/fg1 et al.); in flattened representatives head is flattened dorsoventrally, but retains hypognathous condition.

Mouth apparatus [see (4)–(7)] is usually non-specialized, in rare cases specialized either for carnivorism, or for filtering, or in other manner. All three maxillary dentisetae can be subequal and slender (Kluge 2004: Fig.28:D) or distal dentiseta is thickened, stout and pressed to canines (Kluge 2004: Fig.28:B) (similar to Nesameletus/f1=Metamonius/g1). Maxillary palp can be 3-segmented, in some groups independently becomes 2-segmented. Labial palp is usually 3-segmented, 3^rd segment is usually immobile fused with 2^nd, but in 2^nd segment muscle-adductor of 3^rd segment is usually retained; in rare cases labial palp is 2-segmented, without this muscle.

Larval legs are either slender with setae short and irregular, or have muscular widened femora with long setae forming regular row on outer margin; usually legs are able to stretch posteriorly, but in some rheophilous species lost this ability, being enlarged and widely separated (Kluge 2004: Fig.9:F-H). Usually gill-processes are absent, but selected unrelated species have gills on coxal base (some Baetiella/g1, Camelobaetidius/g1, Heterocloeon/g1 and others) or on coxal apex (some Baetodes/g2).

Larval abdomen is usually long, able to make undulate swimming movements, but in some rheophilous species is shortened and unable to undulate (Kluge 2004: Fig.9:F-G). Abdominal terga are usually simple, rarely with unpaired median or paired submedian projections.

Usually all tergalii I–VII are present; only in selected species tergalii I or VII are lost; in Baetodes/g2 tergalii VI–VII are lost; in selected species tergalii I–II or I–IV are lost. Usually all tergalii have normal dorsal attachment on posterior margins of segments, only in Afrobaetodes, Baetodes/g2 and Raptobaetopus/g1 sartorii [Cymbalcloeon] tergalial bases are transferred ventrally. Tergalii [with anal ribs on anal margin – see Tetramerotarsata (12)] are often oval, with entire margin bordered by costal and anal ribs; sometimes anal rib is vestigial or lost, in this case tergalius can have anal expansion; in Callibaetis such anal expansion is bent ventrally, in Cloeon/fg1 – dorsally, thus in both cases tergalius becomes bilamellate (the same in some other mayflies – see Index of characters [1.3.24]); in Callibaetis costal rib locates far from costal margin; in Baetodes/g2 both tergalial ribs are lost. In some taxa (e.g., Cloeon/fg1, Callibaetis) tergalii retain ability of rhythmical respiratory movements; in other taxa (e.g., Baetungulata) ability of such movements is lost (see Index of characters [1.3.30]).

Larval caudalii are usually not long, with dense primary swimming setae and without secondary swimming setae, cerci with oblique segment boundaries; but in some rheophilous species cerci are elongate, sometimes primary swimming setae are completely lost; in other species, vice versa, besides primary ones, secondary swimming setae appear ( see Index of characters [1.3.67]). Larval paracercus is usually well-developed [while imaginal paracercus is vestigial – see Liberevenata (7)], but in some rheophilous species larval paracercus is more or less shortened or vestigial.

Eggs have no anchors, with various chorionic sculpture; in two taxa (Cloeon/fg2 and Callibaetis) viviparity evolved independently.