CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Geminovenata.

(1) Bases of tergalii I are transferred to ventral side of body, while tergalii II–VII retain their dorso-lateral position (Kluge 2004: Fig.43:A). Unique apomorphy: in other mayflies in that very rare cases when tergalii bases are transferred ventrally (Behningia/fg2, Raptoheptagenia and others), tergalii of all pairs have the same position. In Geminovenata, as in all other mayflies, all tergalii are attached to tergites, but abdominal tergite I is expanded ventrally and supplied with a pair of lateral longitudinal ridges in such a manner, that its tergalii look as being attached to sternite; correct homology of parts of 1^st abdominal segment can be understood if trace development of subimaginal and imaginal tergite and sternite from larval parts (Kluge 1989a: Fig.5: 8-10). The ventral tergalius I either retains the same structure as the dorsal tergalii II–VII, or differs [see Homoeoneuria/g2 (3) below].

(2) Winged stages are short-living; legs are non-functional. Moult from subimago to imago is partial: subimaginal cuticle is shed from abdomen and partly from thorax, but does not shed from wings and legs (unique apomorphy – see Index of characters [2]). On all legs of male [including fore legs – see Discoglossata (7)] 1^st–4^th tarsal segments are usually shortened, with strongly inclined boundaries, can be fused together or reduced in number, all claws are blunt; legs of female are even more reduced, curved, with tarsal segmentation non-expressed, claws vestigial or lost (Kluge 2007: Fig.13).

(3) Wings [with gemination – see Discoglossata (5)] are highly modified: longitudinal veins are closely united in pairs, intercalaries are strongly reduced in number, thus spaces between pairs of longitudinal veins are strongly widened; crossveins demonstrate tendency to disappearance (Demoulin 1952b: Fig.1-2; Kluge 2004: Fig.49:A-B, 50:A-B, 51:A-B; Kluge 2007: Fig.21-22).

On fore wing RSa always lacks branches and intercalaries, MA always lacks intercalary iMA; among intercalaries, only iRS and iMP can be retained (sometimes they are also lost). Cubital field [see Anteritorna (1)] includes a single strong convex vein ("CuA₂") arising from CuA to basitornal margin and looking as a branch of CuA (the same in some short-living Fossoriae – see Index of characters [2.2.51]). Hence, behind RA, always following double veins are present: RSp+MA₁, MA₂+MP₁, MP₂+CuA and "CuA₂"+CuP; usually there is also a double vein RSa+iRS (but sometimes RSa and iRS are lost), sometimes also a singe vein iMP is present. Bifurcation of MA [initially situated near middle of wing – see Euephemeroptera (2)] is transferred close to wing base (Kluge 2004: Fig.50:A, 51:A); only in Elassoneuria/g1 it is situated nearer to middle of wing, probably being transferred their secondarily (Kluge 2004: Fig.49:A).

On hind wing intercalaries are completely lost; MA is non-branched [see also Variable characters of Chromarcys] and like on fore wing, is bordered by two neighbouring veins – RSp and MP₁.

Dense cross veins can be present on larval protoptera, but during transformation to adult they can partly or completely disappear (Demoulin 1953a: Fig.3; 1975: Fig.1-3; Kluge 2007: Fig.19-22, ).

(4) Imaginal mesonotal suture has a form of wide membranous stripe and is curved posteriorly as a whole, thus it crosses medioscutum not at anterior, but at middle or posterior part, dividing it to two separated sclerites (Kluge 2004: Fig.46:A; Kluge 2007: Fig.13). Unique apomorphy (see Index of characters [2.2.8]). At least in investigated Oligoneuriella/fg1 subimaginal cuticle of mesonotum is not sclerotized at all, being very thin, that allows to shad exuviae at flight breaking it [see (2)].

(5) Anterior paracoxal suture on ventral side of mesothoracic episternum is strongly curved posteriorly, thus terminating not at basisternum, but at anterior margin of furcasternal protuberance, and anepisternum is much larger than katepisternum (Kluge 2004: Fig.46:C-D). Unique apomorphy.

(6) Male genital apparatus has peculiar structure (Kluge 2004: Fig.46:B, 47, 48, 49:C-F, 50:D; Kluge 2007: Fig.23): Pedestals of gonostyli are lost, and muscles moving gonostyli are diminished (unlike other Eusetisura, which have large gonostyli pedestals with strongly developed muscles). Gonostyli themselves usually are not diminished, but soft and weak; in Homoeoneuria/g2 and Fittkauneuria gonostyli are lost. 1^st and 2^nd segments of gonostylus are fused (unlike Chromarcys, where they are separated). Left and right penis lobes are movably connected and have various structures allowing them to protract [see below, Oligoneuriella/g1 (1), Homoeoneuria/g2 (7), Elassoneuria/g1 (3) and Oligoneuria/f4=g5 (3)].

(7) Imaginal and subimaginal caudalii [cerci and paracercus – see Plesiomorphies of Discoglossata] are modified. In subimago caudalii are as short as in larva, more or less retaining larval structure (i.e. joinings can be oblique, primary swimming setae can be developed). In male imago caudalii are long, soft, usually lack irregularly situated setae (peculiar for majority of mayflies, including Chromarcys), but have whorls of long setae on apex of each segment; such structure is present at least in the species examined of Oligoneuriella/g2, Oligoneurisca, Homoeoneuria/g2 and Elassoneuria/g2; but sometimes (particularly in Lachlania/g1 powelli [L.]) cerci of male have irregularly situated setae.

(8) In larva, subimago and imago abdominal tergite X has lateral-ventral margins longitudinal, as long as the segment, reaching bases of cerci; latero-posterior angle of tergite forms a ventral condylus for cercal base and separates paraproct from cercotractor; cercotractor is transformed to a narrow semicircular sclerite exposed caudally and surrounding lateral half of cercal base (Kluge 2004: Fig.12:G), can be fused with cercal base. The same in Fossoriae and Caenotergaliae (but not in Chromarcys and other mayflies, whose lateral-ventral margins of tergite X are oblique, not articulating with cerci, and cercotractors are triangular, exposed laterally and widely connected with paraprocts).