CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Ametropus.

(1) Larva has peculiar body form adapted to behaviour on sandy ground in running waters (Keffermuller 1959: Pl.II; Allen & Edmunds 1976: Fig.1-2; Kluge 2004: Fig.25:A-B; ): Head, while retaining hypognathous position, is relatively short, with eyes transferred anteriorly and ocelli brought together. Thorax and abdomen are flattened. Pronotum has rounded paranotal lobes. Mesonotum anteriad of fore protoptera has one more pair of paranotal lobes, separated from the protoptera by a pair of oblique incisions (Kluge 2004: Fig.25:A) (unique apomorphy). Margins of prothoracic and mesothoracic paranota are fringed with long hairs (Kluge 2004: Fig.25:B). Fore protoptera are spread, their costal margins somewhat diverge posteriorly (while in other Euplectoptera costal margins of fore protoptera never diverge, even in similarly flattened psammophilous Pseudiron). On all legs, especially on middle and hind ones [about fore legs see (3)] tibiae are shortened, and claws are elongate, slightly arched, without denticles (the same in other psammophilous mayflies – Acanthametropus/fg1 and Pseudiron).

(2) Mouth apparatus is somewhat modified (Keffermuller 1959: Pl.III; Allen & Edmunds 1976a: Fig.11-16): Labrum and hypopharynx with wide median incision apically. Biting margin of maxilla [bearing 3 dentisetae – see Anteritorna (2)] is narrow; apex with 2 canines (instead of three initial ones); apical margin lacks setae (Kluge 2004: Fig.25:D) (non-unique apomorphies – see Index of characters [1.1.33] and [1.1.31]). Labial palp (3-segmented) has 1^st segment enlarged, with flexor of 2^nd segment strongly widened, fan-form, proximally attached not only to base, but also to outer side of 1^st segment; 2^nd segment (penultimate) with more or less expressed inner-apical projection.

(3) Larval prosternum and fore legs have unique structure (Kluge 2004: Fig.25:B): Prosternum bears a lamellate process with setae on its apex (subimago and imago have similar process, but without setae). Larval fore legs are smaller than others, palp-like; fore coxa bears a long process directed medially, toward the prosternal process, and covered with long setae. Tibia-tarsal articulation is shifted to anterior side, unlike middle and hind legs, where it retains normal position on outer side (the same in subimago and imago). Larval fore claw bears long setae all over its length, like other leg segments (unique apomorphy).

(4) In male and female imago and subimago both claws of fore leg are blunt (unique apomorphy: in other mayflies with functional legs only male can have both fore claws blunt – see Index of characters [2.2.77] and [2.2.79]).

(5) All tergalii I–VII are large, lie in one plane; each tergalius is nearly round, entire margin is bordered by rib and bears long setae (Keffermuller 1959: Pl.II:2).

(6) Larval caudalii, besides well-developed primary swimming setae, have secondary swimming setae on lateral sides of cerci. Non-unique apomorphy (see Index of characters [1.3.67]).

Characters of Ametropus of unclear phylogenetic status.

(7) On fore wing CuP terminates close to tornus [see Anteritorna (1)]; AA is very long, terminates not far from tornus (Kluge 2004: Fig.24:C) (thus wing venation somewhat resembles that of Posteritorna).

(8) Cubital field of fore wing [in most part terminating anteriad of tornus – see (7)] with 2 pairs of intercalaries, among which anterior par is long, and posterior short (Kluge 2004: Fig.24:C). Non-unique apomorphy (see Index of characters [2.2.52]).

(9) On hind wing MA lacks furcation, and MP₂ has a form of intercalary, thus a single triad RS is retained [see Euplectoptera (1)] (Kluge 2004: Fig.24:D). Non-unique apomorphies (see Index of characters [2.2.67], [2.2.69] and [2.2.70]). In other respects hind wing is well developed, as long as 0.4 of fore wing length.

(10) Egg (studied for a single species fragilis [A.]) has peculiar structure: one pole bears a bunch of anchors; each anchor consists of a long thread and a terminal disc; before oviposition, each thread is folded at least three times in such a manner, that all anchors together form a cap-like polar formation externally covered by the terminal discs (Kluge & al. 1995: Fig.76). This polar formation externally resembles polar cap of Polymitarcys/f2=Ephoron/g3 (see Index of characters [3.6]), but unlike it, in Ametropus threads are not fused into integral cap, and can be stretched becoming much longer than the initial formation.

Plesiomorphies of Ametropus. Maxillary and labial palps are 3-segmented. Larval (and adult) patella-tibial suture is developed on middle and hind legs only. Larval paracercus is subequal to cerci.

In imago and subimago: Mesonotal suture is transverse (Kluge 2004: Fig.25:C); anterior paracoxal suture is complete (unlike Rallidens and some Bidentiseta); furcasternal protuberances are contiguous (unlike Amphinotic groups of Tridentiseta and some others – see Index of characters [2.2.23]). Subimaginal lateral pigmented area of mesonotum is small, stretches along lateroparapsidal suture and does not occupy sublateroscutum (Kluge 2004: Fig.25:C) (see Index of characters [2.2.14]). Tarsi are 5-segmented, 1^st segment is fused with tibia and non-shortened. Claws are ephemeropteroid [except for fore legs – see (4)]. Gonostylus with 2 distal segments. Imaginal and subimaginal paracercus is subequal to cerci.