CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies belonging to Prosopistoma/f1=g2 (incl. †Proximicorneus) for certain

(1) Wing venation is greatly modified, unique (Kluge 2004: Fig.16:A-C). Crossveins are completely lost both on fore and hind wings. On fore wing at least behind RS all veins are radiating from base in a fan-form manner; MA lacks furcation, thus MA₂ is lost. In female on fore wing intercalaries are lost besides iMP (which begin near wing base and look like other longitudinal veins). Hind wing has similar structure in male and female, narrow, with costal projection transferred proximally, with numerous fan-form intercalaries, which can be hardly homologized. 

(2) Imaginal and subimaginal mesonotal suture is strongly curved posteriorly on each side; only its median portion is expressed as a pair of sutures, diverging from middle line backward under acute angle; in imago area outlined by these sutures is non-sclerotized (Kluge 2004: Fig.16:F) (see Index of characters [2.2.8]).

Autapomorphies belonging either to Prosopistoma/f1=g2, or Prosopistoma/f2=g3 (males and larvae of †Proximicorneus are unknown)

() In male two long intercalaries are present by sides of each of fan-form radiating veins (RSa, iRS, RSp, MA, MP₁, iMP, MP₂, CuA, CuP, AA) and several intercalaries are present before RSa and behind AA; intercalaries bordering longitudinal veins are new formations absent in other mayflies. 

() Larval mouth apparatus is strongly modified and specialized for carnivorism (Eaton 1883-1888: Pl.43:4-8). Labrum is widened. Asymmetry of mandibles is lost; mandible is strongly elongate along axis of its articulation, mola is completely lost (less complete reduction of mola took place in some other carnivorous mayflies). Superlinguae are completely lost (the same in some other carnivorous mayflies). Maxilla [see Posteritorna (7)] has a single long canine (instead of initial three ones) and 3 dentisetae, which being pressed to canine, form something like an integral claw (Kluge 2004: Fig.15:A). 2^nd segment of maxillary palp is curved so that its inner side is convex. Submentum is very strongly enlarged, its lateral lobes [see Posteritorna (7)] are projected forward, covering from below lateral parts of the rest of labium with labial palps, and anteriorly they reach labrum and anterior-lateral margins of head (unique apomorphy); mentum, glossae and paraglossae are fused forming an integral plate widened distally. Variuos species can be either really carnivorous, or eat detritus and algae (Fontaine 1980).

() Larva has lens-like body form (Kluge 2004: Fig.15:B; Eaton 1883-1888: Pl.43:1-2): head is strongly widened, with rounded anterior margin; lateral margins of notal shield [see Posteritorna (3)] are rounded, without projections (unlike Baetisca/f2=g1); when abdominal segments VII-X and caudalii are retracted [see (3)], larval body together with head in dorsal view has a shape of regular oval; dorsally it is evenly convex with median longitudinal keel on notal shield, ventrally – flat. Integrity of flat ventral surface is completed by expanded mentum covering mouthparts from below [see (1)]. Abdominal segments up to VI inclusively are fused immobile one with another and with thorax; while dorsally they are separated by sutures, ventrally only suture between segments V and VI is retained. Lateral margins of segment V have a pair of incisions; thus, between this segment and epipleura [see Posteritorna (3)] there is a pair of distinctly outlined apertures, which lead to a gill chamber. Femora can be inserted into concavities on thorax and abdomen, and concavities for hind femora convergent posteriorly under acute angle in area of abdominal sternum IV. 

() Abdominal segment X and caudalii have unique structure (Kluge 2004: Fig.15:B). Larval and imaginal tergite X and paraprocts are elongate, rectangular, paraprocts are expanded behind bases of caudalii. Larval (but not imaginal) caudalii can be completely retracted inside abdomen thanks to a pair of long apodemes, which stretch from anterolateral angles of tergite X anteriorly and serve for attachment of the tergal-caudalial muscles.

() In imago [which is present in male only – see (4)] amphitornal margin of wing bears setae; these setae are smaller than in subimago or in female and unlike them, are present on a part of setae-bearing tubercles only (Kluge 2004: Fig.16:B-C). Non-unique apomorphy (see Index of characters [2.2.27]).

() Male imaginal eyes are not enlarged, as small as in female (non-unique apomorphy – see Index of characters [2.1.3]). In both sexes eyes are small, spherical, widely separated, with narrow bases (Gillies 1954: Fig.14).