CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Fossoriae.

(1) Larval legs are initially specialized as burrowing. Fore leg [articulated to vestigial apodeme-bearing pleurite – see Furcatergaliae (1)] is usually strengthened, its tibia is thickened (only in Behningia/fg2 fore legs secondarily lost burrowing specialization and become palp-like, but in related Behningia/fg1-Protobehningia the burrowing of fore legs is retained). In all representatives (including Behningia/fg2) on femora of fore and middle legs anterior side (which in other mayflies is directed more or less dorsally) is concave, bare, most time directed inward, while posterior side (which in other mayflies is directed more or less ventrally) is convex, setose, most time directed outward; femur of hind leg, vice versa, has anterior side convex, setose and most time directed outward, and posterior side concave, bare, most time directed inward (Kluge 2004: Fig.70:C, 73:E). This difference in femoral structure is present not only in that representatives of Fossoriae that use their legs for burrowing, but also in Behningia/fg2, whose legs strongly changed their specialization; in Behningia/fg2 the opposite curvations of middle and hind femora are retained in spite of the fact that deeply specialized middle and hind legs have similar function (Kluge 2004: Fig.73:A–B).

In all other mayfly larvae the outer (usually most convex and most setose) side of femur of all legs is their anterior (dorsal) side. This is true also for Exeuthyplocia/fg1, which have burrowing specialization evolved independently from Fossoriae (see above).

Probably, the following structure of fore tibia is initial for Fossoriae: apical margin projects posteriad of tarsus base and forms two projections – outer-apical and inner-apical ones, with incision between them (Kluge 2004: Fig.74:D–E). Such tibia shape is present in Ichthybotus, Hexagenia/fg1 (among Ephemera/fg9) and Palingenia/f2=g1 (among Cryptoprosternata); presence of the same tibial structure in these non-related groups testifies in favour of its presence in the common Fossoriae ancestor. However, in other Fossoriae fore tibia has more simple shape and looks as more "primitive" (Kluge 2004: Fig.70:C, 77).

(2) Larval frons forms a shelf-like projection with flat dorsal surface. Usually this frontal projection hangs over clypeus and mandibular bases (Kluge 2004: Fig.70:C,E, 75:C, 76:A–C), but in some representatives it is poorly expressed or non-expressed. Similar projection independently appeared in some other mayflies (particularly, in Drunella/g1). Unlike Fossoriae, in Euthyplocia/fg1 projection of similar shape is formed not by frons, but by clypeus (Kluge 2004: Fig.69:F, I).

(3) All tergalii I–VII [modified – see Fimbriatotergaliae (6)], while retain lateral attachment, at rest are bent dorsally-medially-posteriorly (Kluge 2004: Fig.70:C) (with exception for Behningia/fg2, whose tergalii are attached ventrally because of expanded lateral tergal projections).

(4) On imaginal and subimaginal mesothorax epimeron and lateropostnotum [with crest on anterior margin – see Fimbriatotergaliae (4)] are fused by their ends, forming an integral framework (Kluge 2004: Fig.71:D, 78:C). The same in Euthyplocia/fg1, while in Potamanthus/fg1 and Neoephemera/fg1 ends of epimeron and lateropostnotum are separated by membranous concavity (Kluge 2004: Fig.83:C).

(5) 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 either transformed to a narrow semicircular sclerite exposed caudally and surrounding lateral half of cercal base (Kluge 2004: Fig.12:G), or is completely fused with cercal base. The same in Caenotergaliae and Geminovenata (but not in Potamanthus/fg1, Euthyplocia/fg1 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).

Plesiomorphies of Fossoriae. Larva retains long abdomen able to make undulate swimming movements (Kluge 2004: Fig.70:C); caudalii retain dense secondary swimming setae on outer sides of cerci [see Furcatergaliae (6)] and more regular longitudinal rows of more stout primary swimming setae on median sides of cerci and lateral sides of paracercus (only in Campsurus/fg1 longitudinal rows of primary setae are substituted by transverse rows). Hind wing is always well-developed, as long as 0.3–0.5 of fore wing lenght (Kluge 2004: Fig.71, 75, 78, 79, 80).