CLADOENDESIS OF EPHEMEROPTERA

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(1) Tergalii beginning from II [initially bilamellate, with bearing marginal processes – see Fimbriatotergaliae (6)] have unique structure (Kluge 2004: Fig.82:D–E, 88:A) [about tergalius I – see (7)].

Tergalius II has a form of gill operculum: able to cover tergalii III-VI and lost ability for rhythmical respiratory movement (non-unique apomorphy, the same in Posteritorna and selected Pantricorythi – see Index of characters [1.3.32]). Shape of the gill operculum is roundish-quadrangular, with prominent anal-proximal angle reaching middle of posterior margin of abdominal tergum II. In this place the posterior margin of tergum II usually has a median projection (which is absent in Brachycercus/f1=g3 only). Gill operculum [lacking primary marginal ribs – see Furcatergaliae (5)] is usually strengthened by secondary ribs: a proximal rib stretches obliquely from tergalial base (i.e., from its anterior-lateral angle) toward middle; a median rib stretches longitudinally from initial anal-proximal angle (i.e., anterior-middle angle) to initial distal margin (i.e., posterior margin). These two ribs can be independent [see Neoephemera/fg1 (1) below], or connected in the middle of tergalius, forming an integral Y-shaped rib [see Caenoptera (18) below].

Tergalii III-VI have unique form: semicircular, with marginal processes pectinatedly branching (only in Madecocercus processes of tergalii IV-VI are non-branching); any ribs are absent. Bases of tergalii VI are strongly transferred anteriorly, that allows these tergalii to be hidden under the gill opercula (unlike other operculate-gilled mayflies – see [1.3.57]).

Ventral lamella of tergalii II-VI is either diminished (in Neoephemera/fg1), or lost (in Caenoptera).

Tergalii VII are lost (non-unique apomorphy – see Index of characters [1.3.21]).

Tergalii II-VI lie dorsally on abdomen and are directed by their apices posteriorly, overlapping tergalii located posteriad of them; lateral margins of abdominal segments are often expanded laterad of tergalii. Tergalii II (gill opercula) are unable to rhythmic respiratory movements; they can rise up and enable tergalii III-VI to oscillate.

(2) Larval fore protoptera are fused with notum not only by their basitornal margins (as in majority of mayflies), but at least partly by their tornoapical margins as well. At the same time, unlike Coloburiscus/fg1, Discoglossata and Ephemerella/fg1, left and right fore protoptera in Caenotergaliae are not fused one with another, but each of them is fused with notum only; because of this, in Neoephemera/fg1 whose scutellum is non-enlarged, protoptera remain to be free in most part (Kluge 2004: Fig.82:F); in Caenoptera whose scutellum is strongly elongated, protoptera appear to be fused with it nearly all along their length (Kluge 2004: Fig. 88:B).

(3) Larval protopenis is lost, thus subimaginal penis develops inside larval sternum IX, and in mature larva subimaginal penis and styliger are covered by a common cuticular sheath of larval subanal plate (Kluge 2004: Fig.81:D, 82:H, 84:B); separate larval protogonostyli can be either retained, or fused [see Caenis/f3=g1 (2) below]. 

In other mayflies (except for Turbanoculata) larva of last instar has distinct protopenis which has its own larval cuticle and projects posteriad from articulatory membrane between subanal plate and paraprocts (Kluge 2004: Fig.33:F); such protopenis is retained even if protogonostyli are completely fused with subanal plate (Kluge 2004: Fig.98:C).

(4) Imaginal and subimaginal furcasternal protuberances are separated, metathoracic nerve ganglion is inserted between them. Non-unique apomorphy (see Index of characters [2.2.23]); among Fimbriatotergaliae the same independently evolved in Campsurus/fg1 only.

Apomorphies of Caenotergaliae common with Potamanthus/fg1 and Ephemerella/fg1 (see Classifications of Furcatergaliae I).

(5) In larva [which has a collar on pronotum – see Fimbriatotergaliae (1)] mesonotum also has a collar – a concave band at anterior margin, separated from the rest part of mesonotum by a transverse crest (Kluge 2004: Fig.82:F, 88:B). The same in Potamanthus/fg1 and Euthyplocia/fg1, and the same mesonotal collar in Ephemerella/fg1.

(6) Dorsal (anterior) surface of larval fore femur can bear a transverse row of setae (Provonsha 1990: Fig.82); sometimes this row is irregular, indistinct or lost. The same in Potamanthus/fg1 and Ephemerella/fg1.

(7) Tergalius I [different from others – see Fimbriatotergaliae (6)] is stick-like, setose, attached on a prominent cylindrical pedestal arisen from anterior part of the abdominal segment I close to metathorax (the same in Potamanthus/fg1 and Ephemerella/fg1 only); pedestal is sclerotized; tergalius itself is either integral (Kluge 2004: Fig.88:A), or subdivided to 2 segments (Kluge 2004: Fig.82:B) (the same in Potamanthus/fg1).

(8) Egg can have one or two polar caps; usually such cap in dormant stage looks as integral (Provonsha 1990: Fig.112–120), but in a few species of Caenis/f4=g2 cups are formed by very long spirally coiled threads. One cap is present in

Brachycercus/f1=g3, one or two caps – in selected species of Caenis/f3=g1; in Neoephemera/fg1 and many Caenis/f3=g1 caps are absent.

(9) Cubital field of fore wing [see Anteritorna (1)] with bifurcate vein arising from CuA (Kluge 2004: Fig.81:A, 86:F: x₁, x₂); in selected specimens these two branches independently arise from CuA; other veins can be absent [see Caenoptera (10) below], or 1 or 2 simple or branched veins arise from CuA more distally. The same, besides Potamanthus/fg1 and Ephemerella/fg1, in some other mayflies (see Index of characters [2.2.51]).

Characters of Caenotergaliae of unclear phylogenetic status: possible reductions.

(10) Mandibular tusks are absent [see Fimbriatotergaliae (8)]. 

(11) Dense setae on inner side of hind femur and tibia are absent [see Fimbriatotergaliae (9)] .

(12) 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 Geminovenata (but not in 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 Caenotergaliae. Maxilla [without apical-ventral row of setae – see Fimbriatotergaliae (10)] always has 3 canines, 2 dentisetae [see Bidentiseta (1)] and no apical field of setae adjacent to canines (unlike Potamanthus/fg1, Euthyplocia/fg1 and Ephemerella/fg1); usually maxilla is biting, only in Clypeocaenis/g1 specialized as filtering. Larval paracercus is always well-developed, subequal to cerci (while imaginal paracercus can be either well-developed, or vestigial). Imaginal and subimaginal claws are ephemeropteroid [except for fore legs of male – see below, Leucorhoenanthus (2), Potamanthellus (3) and Caenoptera (16)].