CLADOENDESIS OF EPHEMEROPTERA

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(1) Larval head bears pointed projections (spines) directed anteriorly; these are: a pair of very large spines between eyes and antennal bases, a pair of small spines ventrad of antennal bases and a pair of small spines on lateral ocelli (Tshernova 1972: Fig.4).

(2) Asymmetry of mandibles is lost (but unlike other mayflies with symmetrical mandibles, molae are developed). Each mandible has enlarged incisor and two prostheca-like structures, among which the distal one is probably a vestige of kinetodontium (Tshernova 1972: Fig.4).

(3) In larva fore femur is widened in its proximal part, with denticulate inner margin (Tshernova 1972: Fig.4); its shape resembles that of many Drunella and probably is also used for grasping prey.

(4) Hind wing has characteristic roundish shape with strongly arched fore margin (Kluge 2004: Fig.95:B). In other respects it retains plesiomorphic features: Sc reaches wing apex, RS forms a triad (unlike Teloganodes/f1=g3, Teloganella and Tricoryptera). Behind MA [simple — see Furcatergaliae (4)], venation is variable: in dabieshanensis [V.] it consists of simple longitudinal veins and intercalaries; in thani [V.] and ornata [E.] MP is simple, but CuA and CuP form secondary triads not found in other mayflies.

(5) On maxilla all three canines are completely fused forming a single elongate canine (Kluge 2004: Fig.95:C). Non-unique apomorphy; the same in Teloganodes/f1=g3. Maxilla is biting, with field of apical setae small [see Ephemerella/fg1 (16)] and both dentisetae retained [see Bidentiseta (1)].

(6) Fore wing has marginal intercalaries connected with longitudinal veins (Kluge 2004: Fig.95:A). Possibly this is a plesiomorphy, as the same in majority of Ephemeroptera apart of Ephemerella/fg1; but such condition never occurs in other Ephemerella/fg1, which have either free, or non marginal intercalaries (see Index of characters [2.2.55]).

Plesiomorphies of Vietnamella. All tergalii I–VII are present (unique plesiomorphy among Ephemerella/fg1 – see Table): tergalius I is stick-like [see Ephemerella/fg1 (13)] (Kluge 2004: Fig.95:D–E); tergalii II-VI with bifurcate ventral lobes bearing numerous marginal processes; tergalius VII with non-bifurcate ventral lobe [see Ephemerella/fg1 (7)]; unlike Melanemerella/f1=Teloganodes/g1 and some others, tergalii II are not operculate. Larval abdominal terga with paired submedian projections [see Ephemerella/fg1 (19)] (Tshernova 1972: Fig.3a).

In imago and subimago: Eyes of male are large (unlike some Tricoryptera and others). Imaginal and subimaginal mesonotum has structure primitive for Ephemerella/fg1 [see Ephemerella/fg1 (9) and (10)]: mesonotal suture is distinct, lateroparapsidal suture is curved laterally; subimaginal lateral pigmented area of mesonotum is bordered by relief line; scutellum is not modified, infrascutellum is present (as in Ephemerella/fg2 and Ephemerellina/g1, unlike Teloganodes/f1=g3 and Tricoryptera). Cubital field of fore wing has up to 3 bifurcate veins arising from CuA (Kluge 2004: Fig.95:A: x, y, z) [other Ephemerella/fg1 have no more than two such veins – see Ephemerella/fg1 (15)].