CLADOENDESIS OF EPHEMEROPTERA

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Notes. Here are attributed such different mayflies as Fossoriae and Caenoptera; they have a single common feature [see (1)] that is not enough to prove their relationship; however, the holophyly of Fimbriatotergaliae is proven by synapomorphies of Caenoptera with Neoephemera/fg1 [see below, Autapomorphies of Caenotergaliae] and synapomorphies of Neoephemera/fg1 with Fossoriae, Potamanthus/fg1 and Euthyplocia/fg1 listed here [see (2)–(6)]. Imago of Caenoptera, being sharply different from other Fimbriatotergaliae, has hardly explainable similarity with certain Ephemerella/fg1 (see Classifications of Furcatergaliae II). Most probably, the characters (8) and (9) are also autapomorphies of Fimbriatotergaliae, but they are never present in Caenotergaliae, thus can not be used to argue the holophyly of Fimbriatotergaliae.

(1) Larval pronotum has a collar – a concave band at anterior margin, separated from the rest part of pronotum by a transverse crest; laterally this crest is bent anteriad and terminates near anterior-lateral angle of the pronotum. At this point margin of pronotum can be simple (in some Potamanthus/fg1 and Caenotergaliae – Kluge 2004: Fig.67:B–C, 82:F, 88:A–B) or produced to a denticle (in some Potamanthus/fg1, Euthyplocia/fg1 and Fossoriae – Kluge 2004: Fig.69:G, 70:C); in Behningia/fg1 this denticle is transformed to a setose projection (Kluge 2004: Fig.73:A,E). Possibly, the pronotal collar is homologous with the area separated by V-shaped impression [see Ephemerella/fg1 (4) below].

(2) Adult mesonotal suture is strongly curved posteriorly by sides of median line; both its halves can be stretched posteriorly either moderately (Kluge 2004: Fig.68:F, 71:E), or strongly (Kluge 2004: Fig.71:E); medially they can approximate with median suture, and laterally either approximate with lateroparapsidal sutures (Kluge 2004: Fig.83:F), or disappear (Kluge 2004: Fig.78:D–F, 87:G–H).

Non-unique apomorphy: the same in Leptophlebia/fg1 and some others, but not in Ephemerella/fg1 (see Index of characters [2.2.8]). Extinct taxon Baba has the same wing venation as Fimbriatotergaliae [see (5)], but its mesonotal suture has plesiomorphic transverse shape (see below, Furcatergaliae incertae sedis).

In more primitive representatives of Fimbriatotergaliae – Potamanthus/fg1, Ichthybotus, most Ephemera/fg9 (except for Afromera/g1), Pentagenia among Palingenia/f2=g1, and Neoephemera/fg1 among Caenotergaliae – mesonotal suture is well visible in subimago: subimaginal cuticle of medioscutum and submedioscutum anteriad of mesonotal suture is covered with microtrichia, sclerotized and usually more or less pigmented, and cuticle posteriad of mesonotal suture is smooth and non-pigmented. In these representatives lateral pigmented area of subimaginal mesonotum occupies the whole lateroparapsidal suture and area laterad and behind it (i.e. sublateroscutum, lateroscutum and posterior scutal protuberance); thus subimaginal mesonotal pigmentation has a characteristic pattern (Kluge 2004: Fig.68:F, 71:E, 83:F). In imago mesonotal suture can be either also well-expressed (in Neoephemera/fg1 – Kluge 2004: Fig.83:E), or poorly visible, as the whole mesonotal cuticle is smooth and can be evenly sclerotized and pigmented.

In various shortly-molting representatives with modified adult structure – Polymitarcys/f1=Ephoron/g2, Palingenia/f3=g2 among Palingenia/f2=g1 and Caenoptera among Caenotergaliae – subimaginal mesonotal pigmentation is lost, but mesonotal suture is well-expressed in imago: imaginal cuticle behind-mediad of mesonotal suture is weakly sclerotized and non-pigmented, forming a medionotal membrane (Kluge 2004: Fig.78:D). Median portions of left and right halves of the mesonotal suture can run longitudinally parallel to the median suture, in this case the medionotal membrane is opened posteriorly (Kluge 2004: Fig.78:E); in some taxa (Caenoptera and selected Polymitarcys/f1=Ephoron/g2) these portions convergent posteriorly, and the medionotal membrane is closed (Kluge 2004: Fig.78:F, 87:G). Imaginal cuticular pigmentation can be masked by colour of internal tissues, in this case outline of the medionotal membrane is visible only after treating by alkali; but in all Caenoptera and some others it is distinctly visible on intact specimens as well.

(3) Lateroscutal suture stretches from suralare posteromedially, being nearly straight; its posterior end is not curved laterally. This character is expressed in Potamanthus/fg1, Euthyplocia/fg1, Fossoriae and Neoephemera/fg1, being especially well visible in subimago (Kluge 2004: Fig.68:F, 71:E–F, 74:A, 78:E–F, 83:F), but is not expressed in Caenoptera whose mesonotum is highly modified (Kluge 2004: Fig. 87:H). In other mayflies posterior end of lateral scutal suture is curved laterally (Kluge 2004: Fig.6, 90:D, 106:D–E).

(4) Subimaginal lateropostnotal crest begins from anterior margin of postsubalar sclerite and runs in ventral direction by margin of subalar conjunctiva (Kluge 2004: Fig.71:D, 83:C). This is visible on representatives whose subimaginal cuticle has distinctly pigmented sclerites (Potamanthus/fg1, Ichthybotus, Ephemera/fg9, Pentagenia, Neoephemera/fg1), but it is non-expressed in representatives with colourless cuticle (Palingenia/f3=g2 and Polymitarcys/f1=Ephoron/g2). In Caenoptera lateropostnotum is strongly modified and lacks this character (Kluge 2004: Fig.87:A) [see Caenoptera (1) and (8) below]. In majority of other mayflies lateropostnotal crest begins from postsubalar sclerite at a distance from its anterior margin and passes at a distance from margin of subalar conjunctiva, thus subimaginal sclerotization of lateropostnotum has a axe-like shape (Kluge 2004: Fig.5:D, 90:C).

(5) In proximal part of fore wing MP₂ and CuA are curved and divergent from MP₁ (Kluge 2004: Fig.68, 69, 71, 75, 78, 79, 80, 81). This curvation is more or less expressed in all Fimbriatotergaliae except for Caenoptera, where it is completely absent (Kluge 2004: Fig. 86:F). In place of curvation MP₂ and CuA can be brought together, sometimes they are fused at some distance, and in this case MP₂ looks as originating from CuA, but not from MP₁ (Kluge 2004: Fig.75:A, 78:A).

On hind wing MP₂ either retains straight shape, or becomes similar to that of fore wing – basally curved and approximated to CuA or originates from CuA (Kluge 2004: Fig.79:B).

The origin of MP₂ (from MP₁ or CuA) on fore and hind wings was erroneously regarded to be characteristic for certain supra-species taxa, however this character varies individually (Lestage 1922: Fig.1A-C).

The same vein curvation as in Fimbriatotergaliae, is present in extinct taxon Baba, which differs from true Fimbriatotergaliae by mesonotum structure (see below, Fimbriatotergaliae INCERTAE SEDIS).

(6) Tergalii II–VII [bilamellate, without marginal ribs – see Furcatergaliae (5)] have numerous marginal trachea-bearing processes. In Potamanthus/fg1, Euthyplocia/fg1 and Fossoriae (formerly united in a taxon Pinnatitergaliae) tergalii have a uniform structure (Kluge 2004: Fig.67:A, 70:C; Eaton 1883–1888: Pl.28–31): each tergalius II–VII has both lamellae well-developed and elongate (length not less than 4 times exceeds its width, if not take into account marginal processes), with numerous (several dozens) non-branched trachea-bearing processes on both sides. Only in lankensis [Ephemera] tergalius VII is non-bifurcate and has processes on one side only. Ribs are usually absent, but sometimes one or two ribs can be present by sides of central trachea as poorly sclerotized semi-cylindrical convexities (especially thick in Palingenia/f3=g2); possibly, these ribs are secondary.

In Caenotergaliae tergalial structure is strongly modified [see Caenotergaliae (1) below]; primitively there are also two lamellae with numerous marginal trachea-bearing processes (Kluge 2004: Fig.82:E), but in Caenoptera ventral lamella is lost.

Tergalius I always strongly differs from others: in Behningia/fg1 it is non-bifurcate (Kluge 2004: Fig.73:A,E); in other Fossoriae and Euthyplocia/fg1 it is strongly diminished and usually lacks processes (only in some Campsurus/fg/fg3 a few processes are present), being bifurcate or non-bifurcate (see Index of characters [1.3.33]), and retaining normal attachment and musculature; in Potamanthus/fg1 and Caenotergaliae it is transformed to a stick-like vestige on a pedestal at anterior part of the segment (Kluge 2004: Fig.67:A), which has the same structure as in Ephemerella/fg1, that is hardly explainable (see Classifications of Furcatergaliae I).

Tergalii II –VII retain ability of rhythmical respiratory movements; in Caenotergaliae tergalii II, being transformed to gill opercula, lost this ability (see Index of characters [1.3.30]).

(7) Chromosome sex determination is XX in female and X0 in male (non-unique character). According to Soldan & Puthz (2000), such sex determination is found in three species of Ephemera/fg10 – vulgata [E.], danica [E.] and lineata [E.], one species of Potamanthus/fg3 – lutea [E.], and two species of Caenis/f3=g1 – horaria [E.] and macrura [C.], while chromosomes of other Fimbriatotergaliae are not examined. In all other mayfly species examined (about 20 species), sex determination is XX in female and XY in male.

(8) Mandible bears a tusk – a process on outer (anterior, or dorsal) side of mandible laterad of incisor. The tusk can be much longer than mandible (in majority of Potamanthus/fg1, Euthyplocia/fg1 and Fossoriae, or in a form of a small denticle (in some Potamanthus/fg1), or reduced to a thin vestige (in Afromera). Among Fimbriatotergaliae only Behningia/fg1 and Caenotergaliae completely lack tusks (see below, Classifications I and II).

Among other mayflies tusks occur only in Leptophlebia/fg1: some representatives of Atalophlebomaxillata have convexity approximately on the same place as the tusk of Fimbriatotergaliae, and in one Australian species doantrange Campbell 1993 [Kalbaybaria] this convexity is produced to a large tusk. In another species of Leptophlebia/fg1 – Paraleptophlebia/g1 packii Needham 1927 [Leptophlebia], mandibular incisor is strongly enlarged and can be erroneously taken for a tusk.

(9) On larval hind leg (but not on other legs) inner side of femur and inner side of tibia (patella and/or telotibia) has dense protruding short stout pointed setae (Kluge 2004: Fig.70:D). Unique character. Among Fimbriatotergaliae these setae are present in Potamanthus/fg1, Euthyplocia/fg1 and most Fossoriae, but absent in Palingenia/f2=g1, Behningia/fg1, and all Caenotergaliae.

(10) Larval abdominal segments have characteristic shape, with lateral margins convex, rounded, and not produced to posterolateral spines (Kluge 2004: Fig.70:C). Among Fimbriatotergaliae such abdominal shape is present in Potamanthus/fg1, Euthyplocia/fg1 and most Fossoriae, but not in Behningia/fg1 and Caenotergaliae which can have well-developed posterolateral spines on segment IX and some previous ones (as in majority of Ephemeroptera).

(11) Maxilla lacks apical-ventral row of setae (unlike many Leptophlebia/fg1, Radulapalpata and Tridentiseta – see Index of characters [1.1.31]).

Plesiomorphies of Fimbriatotergaliae. In most taxa attributed here larval claws have no denticles: subapical denticles or two rows are never present (unlike many Ephemerella/fg1 and Leptophlebia/fg1); one row is present in some Caenis/f4=g2 and on specialized fore legs of Asthenopus/fg1 only. Larval paracercus has the same length as cerci or only slightly shorter (adult paracercus can be developed or vestigial – see Index of characters [2.3.22]).

Classifications of Fimbriatotergaliae. Besides the accepted here division of Fimbriatotergaliae to Potamanthus/fg1, Euthyplocia/fg1, Fossoriae and Caenotergaliae, following taxa were suggested.

I. Pinnatitergaliae Kluge 2000 

In circumscription fits: 

— superfam. Ephemeroidea: Edmunds & Traver 1954a: 239;

— subordo Ephemeroidea: Lestage 1924a: 319;

— Pinnatitergaliae = Ephemera/fg7: Kluge 2000: 251.

This taxon is widely accepted and characterized by uniform structure of tergalii II–VII [bilamellate with marginal processes – see Fimbriatotergaliae (6)]: no one pair is reduced, each lamella is elongate, with marginal processes numerous and non-branched. In other mayflies tergalii can be bifurcate and elongate, but without processes (majority of Leptophlebia/fg1), or with less number of processes (Habrophlebia/fg2 and some other Leptophlebia/fg1), or bifurcate and with numerous non-branched processes, but shorter than in Pinnatitergaliae (Thraulus and some other Leptophlebia/fg1). Thus, structure of tergalii II–VII is a reliable diagnostic character of Pinnatitergaliae. Besides tergalial structure, larvae of Pinnatitergaliae are characterized by presence of dense swimming setae on caudalii [including lateral sides of cerci – see Furcatergaliae (6)]. However, both characters are plesiomorphies in comparison with Caenotergaliae. Other characters of Pinnatitergaliae are either synapomorphic with Caenotergaliae [see Fimbriatotergaliae (1)–(7), or present not in all representatives [see ibid., (8)–(9)]. Thus, most probably Pinnatitergaliae is a paraphyletic taxon ancestral for Caenotergaliae.

In circumscription fits:

— superfam. Ephemeroidea: McCafferty 1991: 349;

— infraordo Scapphodonta McCafferty 1998.

This taxon unites all Pinnatitergaliae (see I) except for Behningia/fg1 – i.e. Potamanthus/fg2, Euthyplocia/fg1, Ichthybotus, Ephemera/fg9 and Cryptoprosternata. An assumption about holophyly of Scapphodonta contradicts the assumption about holophyly of Fossoriae. Following characters could be taken into account as possible autapomorphies of Scapphodonta.

(1) Presence of tusks [see Fimbriatotergaliae (8)].

(2) Lateral margins of larval abdominal segments are rounded, without posterolateral spines [see Fimbriatotergaliae (10)].

(3) Non-pectinate tergalius I [see Fimbriatotergaliae (6)]. 

However, Behningia/fg1 has apomorphies of Fossoriae (see below); larvae of Behningia/fg1 are deeply specialized, that allows to assume that their mandibular tusks disappeared secondarily. Structure of tergalius I is not uniform among Scapphodonta: in this respect Potamanthus/fg1 is similar to Caenotergaliae and principally differs from other Fimbriatotergaliae (see Classifications of Furcatergaliae I). Most probably, the taxon Scapphodonta is paraphyletic.