CLADOENDESIS OF EPHEMEROPTERA

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(1) Mouth apparatus is strongly modified:

Mandible is enlarged, with regular row of long setae on outer margin; lateral end of this row is curved toward ventral side of mandible (Kluge 2010: Fig.4); mandibles have this modification beginning from larvula (Kluge 2010: Fig.31). This mandibular structure is uniform in all species; only in group tinctus incisor projects into a long pointed tusk (Kluge 2010: Fig.38). 

[However, Kimmins (1949) mentioned a mature larva of "?Tricorythus sp." without setal row on mandible].

Maxilla has unique structure (Kluge 2004: Fig.97:A–C): flat, truncate in such a manner that its apical margin is formed by expansion of initial inner (median) margin, and its apical-lateral angle corresponds to initial apical-median angle. Apical canines are lost. A single dentiseta [instead of two – see Bidentiseta (1)] is long and slender, situated near apical-lateral angle. Setae of initial inner-dorsal row are as long as dentiseta, and form a regular row on apical margin; each seta of this row has such basal articulation, which allows it to turn dorsally or distally only. Initial inner-ventral row of setae is lost. Ventral side besides the subapical field of dense ordered setae [see Ephemerella/fg1 (16)] bears a regular transverse row of long setae; each seta of this row has such basal articulation, which allows it to turn ventrally or distally only. This maxillary structure is uniform in all species.

Maxillary palp is long, with slender long arched 1^st and 2^nd segments and small 3^rd segment [while muscles in the maxillary palp are lost – see Ephemerella/fg1 (1)]; only in Sparsorythus maxillary palp is lost.

Maxilla of larvula (examined for tinctus [Tricorythus] only) has inner margin less expanded; its apex bears one apical canine (which disappears in older larva) and one dentiseta (which retains in older larva); apical and ventral setae, peculiar for older larva, are absent; maxillary palp is absent (Kluge 2010: Fig.33).

Probably, initially for Tricorygnatha, larvula has lost maxillary palp, while older larva has long maxillary palp of peculiar structure, uniform in all species. In Sparsorythus maxillary palp is lost in all instars [see below, Sparsorythus (1)]. 

Labium has unique structure (Kluge 2010: Fig.1): submentum is strongly shortened; mentum, glossae and paraglossae [see Ephemerella/fg1 (2)] are fused together forming an integral semicircular plate; these features are expressed beginning from larvula (Kluge 2010: Fig.32). Ventrally the integral semicircular plate bears a pair of fields of long setae; dorsally it has a concavity, whose outline repeats shape of hypopharynx; into this concavity hypopharynx is inserted. Labial palp has 2^nd segment long, arched, with two regular rows of long filtering setae: one row consists of especially long setae and goes along outer margin; another row goes along inner margin; 3^rd segment is very short; in larvula segments of labial palp have less difference in length (Kluge 2010: Fig.32).  

(2) Larval fore protoptera [fused by means of mesial plate – see Ephemerella/fg1 (5)] are fused up to their apices, so that free margin of mesal plate between their apices is not expressed. Thanks to this, mesial plate has triangular shape. In course of transformation to subimago, hypoderm of mesial plate can form a separate unpaired triangular plate with a small apical cleft (Kluge 2010: Fig.35) (instead of a pair of plumidia in some other Ephemerella/fg1); during subsequent transformation to subimago, this plate dissolves, so in winged stages it is absent.

(3) Larval claw has uniform structure in all species: row of denticles on inner margin [see Ephemerella/fg1 (18)] consists of 2 denticles only: a small denticle at base of sclerotized part of claw and a larger denticle close to it; besides these two inner denticles, there are two subapical side denticles – one subapical denticle on each side of claw (Kluge 2010: Fig.10). In stage of larvula claws have quite different structure (Kluge 2010: Fig.34).

(4) Larval abdomen has peculiar structure (Kluge 2010: Fig.13-14): it is not flattened (unlike most Ephemerella/fg1), relatively high, with lateral sides belonging to terga; on segments II–VII these lateral sides form a pair of concavities, into which tergalii can be inserted; tergalii [on segments II–VI or II–VII – see Plesiomorphies] are attached laterally, unlike most other Ephemerella/fg1, whose tergalii are attached dorsally [see Ephemerella/fg1 (7)]; segments VIII–IX, unlike others, are nearly cylindrical, without lateral ridges or laterally expanded flattened lobes and without posterolateral spines (unlike most other mayflies).

(5) Moult from subimago to imago takes place in male only; female subimago does not moult to imago. Besides Tricorygnatha, the same in some mayflies with short-living adults (Prosopistoma/f1=g2, Behningia/fg1, Palingenia/f3=g2, Polymitarcys/f2=Ephoron/g3 – see Index of characters [2]); unlike them, Tricorygnatha are not so shortly-living and retain functional legs.

Apomorphies of Tricorygnatha common with Leptohyphes/fg1 and Caenoptera (see Classifications of Furcatergaliae II).

(6)(2) Imaginal and subimaginal mesothorax [see Tricoryptera (3)–(4)] has following modifications: On mesonotum [see Ephemerella/fg1 (10)] lateroparapsidal suture is not curved laterally, but convergent with medioparapsidal suture; sublateroscutum has a transverse interscutal suture (Kluge 2004: Fig.98:D; Kluge 2010: Fig.27, Fig.42; Fig.80). Anterior paracoxal suture is transferred posteriorly, closer to anterior margin of coxal conjunctiva. The same in Leptohyphes/fg1 and Caenoptera.

(7)(3) On fore wing marginal intercalaries are absent (Kluge 2010: Fig.25-26). Among Ephemerella/fg1 the same in Dicercomyzon and Leptohyphes/fg1 (see Index of characters [2.2.55]); possibly synapomorphy; the same in Caenoptera.

(8)(4) In imago amphitornal margin of wing with setae (as in subimago of all mayflies). Non-unique apomorphy (see Index of characters [2.2.27]); particularly, the same in Leptohyphes/fg1 and Caenoptera.

(9)(5) Hind wings [initially vestigial – see Tricoryptera (2)] are lost. Non-unique apomorphy (see Index of characters [2.2.59]).

(10)(6) In male larva caudalii (cerci and paracercus) are thickened in proximal part (Kluge 2010: Fig.86-89), unlike caudalii of female, which have usual form. In male imago (but not in subimago) caudalii are very long. The same in Caenoptera, Ephemerythus and Leptohyphes/fg1 (Kluge 2004: Fig.103:E–F), unlike Machadorythus and Dicercomyzon.

(11)(7) In imago and subimago tarsi and claws have the following structure (Kluge 2010: Fig.22-24, Fig.50-51, Fig.66-67): 

1^st tarsal segment of all legs is completely fused with 2^nd segment, without suture between them; thus, all tarsi of winged instars are 4-segmented. Besides Tricorygnatha, fusion of 1^st and 2^nd tarsal segments takes place in Machadorythus (where these segments are non-fused only on fore legs of male).

Fore leg of male imago (initially elongate) has length subequal with middle and hind legs (the same in some other Afrotricorythi – see Index of characters [2.2.74]).

On middle and hind legs 1^st segment [initially fused with tibia and shortened – see Furcatergaliae (2)] on its outer side is secondarily distinctly separated from tibia, somewhat resembling that of larva. The same in Tricorythodes, Tricorythopsis and Caenoptera (see Index of characters [2.2.84]).

On fore legs of male claws in imago are blunt, in subimago ephemeropteroid; on other legs claws are ephemeropteroid both in imago and subimago (Kluge 2010: Fig.22-24, Fig.50-51, Fig.66-67); exception is made by species originally attributed Madecassorythus and Ranorythus, whose claws of male imaginal fore leg are said to be ephemeropteroid. The same in some other taxa (see Index of characrters [2.2.77]).

(12)(8) At rest, subimago and imago keep wings spread by sides or somewhat turned up (unlike Dicercomyzon and Ephemerythus, whose wings are raised up, as in most mayflies). Among maylies with functional legs, the same in Leptohyphes/fg1, Caenoptera and a few others; the same in short-living mayflies.

Characters of Tricorygnatha of unclear phylogenetic status.

(13) Selected species have the following sexual dimorphism in shape of pronotum and eyes. 

In some taxa within Tricorygnatha, larva has unusual sexual dimorphism in shape of pronotum (Kluge 2010: Fig.52-53): in male larva fore margin of pronotum is expanded medially as a semicircular flap and overlaps hind part of head; in contrast, in female larva median part of fore margin is straight. Like other larval sexual characters, this one is mostly expressed in last larval instar; in younger male larva median expansion of fore margin of pronotum is less prominent (Kluge 2010: Fig.54). Unlike larvae, adults have no sexual dimorphism in shape of fore margin of pronotum: their pronotum has convex anterior margin, as in other mayflies (Kluge 2010: Fig.70). Such larval sexual dimorphism, which has no any connection with imaginal sexual dimorphism, has not been found in other mayflies. Among Tricorygnatha, the sexual dimorphism in shape of larval pronotum is found in discolor [Oxycypha], exophthalmus [Tricorythus], "Tricorythus sp.R": Kluge 2010, martini [Spinirythus], known species of Madecassorythus (Oliarinony & Sartori & Elouard, 2000), dongnai  [Spinirythus] and bifurcatus  [Spinirythus] (personal communication by P. Sroka). In some species sexual dimorphism in shape of larval pronotum is completely absent; these are: varicauda [Caenis], tinctus [Tricorythus], "Tricorythus sp.N": Kluge 2010 and celebensis [Tricorythus (Sparsorythus)]. The fact that this feature varies among species of the holophyletic taxon Sparsorythus, testifies about its mosaic pattern. Probably, the sexual dimorphism in shape of larval pronotum correlates with large male eyes.

In some taxa within Tricorygnatha, eyes of male are large and divided into a lower portion with black facets and an upper portion with lighter facets. As in other mayflies with large male eyes, this character is expressed both in adults (Kluge 2010: Fig.70) and in larvae of late instars (Kluge 2010: Fig.52-53, Fig.88). Large male eyes are found in discolor [Oxycypha], exophthalmus [Tricorythus], " Tricorythus sp. R": Kluge 2010, bifurcatus [Sparsorythus], jacobsoni [Tricorythus], dongnai [Sparsorythus], all known species originally attributed to Madecassorythus, Spinirythus and Ranorythus. In some species eyes of male are as small as in female; among species examined, these are: varicauda [Caenis], tinctus [Tricorythus], "Tricorythus sp.N": Kluge 2010, "Tricorythus sp.S": Kluge 2010 and celebensis [Tricorythus (Sparsorythus)]. Judging by pattern of this character among Tricoryptera and other mayflies, enlarged male eyes can be either a symplesiomorphy with most mayflies, or an apomorphic reversion. The fact that this feature varies among species of the holophyletic taxon Sparsorythus, testifies about its mosaic pattern. Probably, among Tricorygnatha large male eyes correlate with the sexual dimorphism in shape of larval pronotum.

Plesiomorphies and variable characters of Tricorygnatha. Tergalii II–VI with all lobes completely developed [see Ephemerella/fg1 (7)] (Kluge 2004: Fig.97:F–G) (unlike Dicercomyzon); tergalii II are non-operculate and move synchronously with next ones (unlike Ephemerythus, Leptohyphes/fg1, and some others – see Table) [tergalii I and VII absent – see Tricoryptera (5) and (6)]. Paracercus of larva, subimago and imago is usually well-developed; in species originally attributed to Spinirythus adult paracercus is shortened, especially in male; larval paracercus is as long as cerci, but much thinner. In species attributed to Ranorythus, adult paracercus is shortened in male and non-shortened in female.