CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Liberevenata.

(1) On fore wing MA₂ is free, not connected with MA (Kluge 2004: Fig.27:A, ). Unique apomorphy: only in Prosopistoma/f1=g2 MA is non-branched, in other Euephemeroptera MA₂ nearly always arises from MA and can be free in selected specimens only.

(2) Fore wing with free intercalaries. Non-unique apomorphy (see Index of characters [2.2.55]). The initial condition for Liberevenata is presence of one marginal intercalary in each space – this is peculiar for Palaeocloeon (Kluge 2004: Fig.27:A), plesiomorphon Protopatellata, Cloeon/fg1, Baetopus/g1, Cheleocloeon and Afrobaetodes; in Baetovectata two marginal intercalaries in each space are present.

(3) On fore tarsus of male imago and subimago 1^st segment (fused with tibia) is strongly shortened (Kluge 2004: Fig.27:C,F). Often this 1^st segment, being fused with tibia and shortened, is invisible, thus tarsus looks as 4-segmented; but unlike really 4-segmented tarsi of middle and hind legs [see Tetramerotarsata (1)], fore tarsus has all its 4 segments mobile. Independently from Liberevenata, 1^st tarsal segment had shortened in Furcatergaliae, but there it is shortened on all legs, while in Liberevenata the 1^st segment of middle and hind leg remains to be long.

In female structure of fore tarsus is often generally the same as in male – 5 segments are retained, 1^st of which is shortened; in some species (e.g., costai [Indobaetis] fore tarsus of female is 4-segmented, like middle and hind tarsi [see Tetramerotarsata (1)].

(4) Genital apparatus of male is modified as the following (Kluge & Novikova 2011: Figs 1-3): Median part of styliger is strongly reduced, and its lateral parts remain to be well developed; these lateral parts of styliger represent a pair of gonostyli pedestals, or unistyligers: they are separated one from another by deep and wide incision; each of them is thick, cylindric, bears the gonostylus and contains the muscle going to the gonostylus base (some people wrongly take the unistyligers for the first segments of gonostyli). Penis (which initially has a pair of sclerotized penial arms articulated with the posterior angles of 10^th abdominal tergum and the anterior angles of styliger) is reduced and modified in such a manner, that consists of a more or less sclerotized penial bridge and a pair of sclerotized gonovectes (singular – gonovectis); lateral ends of the penial bridge are articulated with posterior angles of 10^th abdominal tergum; each gonovectis arises from the penial bridge near its lateral end and is directed medially, at rest is invaginated into the IX abdominal segment; a pair of gonovectal muscles go from gonovectes to lateral parts of IX abdominal sternum; gonoducts terminate on apices of gonovectes. 

In the genital apparatus initial for Ephemeroptera, styliger can be turned ventrally as a whole by the single median sternal muscle of IX uromere (i.e. median styligeral muscle) and thanks to this provides protraction of penis (Kluge 2004: Fig.11), in Liberevenata this movement is impossible, because median part of styliger, to which the median styligeral muscle is attached, is reduced.

Probably, the most primitive genital structure among Liberevenata exists in Afroptilum (Fig. ##): the median styligeral muscle is well developed and terminates on a special median styligeral sclerite between the unistyligers; unistyligers are movable, with membranose bases; because of this, when the median styligeral muscle contracts, unistyligers, instead of turning ventrally as a whole, are brought together, so they act as additional, proximal segments of gonostyli; this movement does not provide protraction of penis; gonovectes are movable, so that they can move out of their pockets in caudal direction, passing ventrad of the penial bridge, and protract gonopores.

In selected taxa of Liberevenata genital apparatus is simplified and modified in this or that direction. The median styligeral sclerite can be lost, and the unistyligers can be immovable; in this case protraction of the median styligeral muscle does not provide adduction of the unistyligers; in some taxa the median styligeral muscle is lost (see Index of characters [2.3.7]). Gonovectes can be immovable, fused by their apices with the penial bridge (see Index of characters []), or, vice verse, especially movable and strongly arched [see Baetovectata () below]. Penial bridge can be desclerotized and non-expressed.

Details of genital apparatus are known for recent representatives only; in extinct Palaeocloeon at least external shape of gonostyli pedestals is the same as in recent Turbanoculata.

Some details of genital apparatus are difficult for examination, because last abdominal segments of fresh specimens contain numerous non-translucent white inclusions. Because of them, muscles located in the 9th abdominal segment are invisible on slides in Canadian balsam. These white inclusions can be successfully dissolved in warm water during 2–4 hours. Some species have such kind of abdominal coloration, which disappears after treating by warm water; in this case 9th abdominal sternum with genitals should be detached from the rest of abdomen before treating by warm water.

(5) Gonostylus has 1 distal segment only (instead of two initial ones). Non-unique apomorphy (see Index of characters [2.3.12]). Among Liberevenata, distal segment disappears completely only in Rhithrocloeon/fg1 [see below, Rhithrocloeon/fg1 (1)].

(6) Imaginal and subimaginal paracercus is vestigial (in larva it can be either well-developed, or also vestigial). Non-unique apomorphy (see Index of characters [2.3.22]).