CLADOENDESIS OF EPHEMEROPTERA
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Furcatergaliae (or Ephemera/fg6)

(Panephemeroptera Euephemeroptera Euplectoptera Anteritorna Bidentiseta - Furcatergaliae)

Nomen hierarchicum: Ephemera/fg6 [f:1810; g:1758]  (sine Oligoneuria; incl. Ephemerella, Leptophlebia)

Nomen circumscribens: Furcatergaliae Kluge 1998: 256

In circumscription fits:

— infraordo Furcatergalia: Kluge 1993: 41; Kluge & al. 1995: 105 [non Furcatergalia Kluge 1989]

— Furcatergaliae Kluge 1998: 256

— Furcatergaliae = Ephemera/fg6: Kluge 2000: 251

References. Kluge 1997b; – 1998: *; – 2004: * * *

Autapomorphies of Furcatergaliae.

(1) Pleura of prothorax are modified (Kluge 2004: Fig.106:A): external wall of pleurite is very low at least at area of dorsal coxal articulation, thus fore coxa articulates close to lateral margin of tergite; pleural suture is extremely shortened, indistinct or lost (in other mayflies, as in majority of other Pterygota, pleural suture stretches from the dorsal coxal articulation to dorsal margin of pleurite); the pleurite area dorsad of the coxal articulation is transformed to a slender apodeme (cryptopleurite) deeply penetrating into the body and invisible from outside; being a continuation of the dorsal margin of pleurite, this apodeme is flattened dorsoventrally. This apodeme serves for attachment of pleural muscles – tergo-pleural, pleura-coxal and cranio-pleural ones. A part of pleurite posteriad of the apodeme is variable, in different representatives can be either low and vestigial, or rather high and well visible externally. This pleurite structure is characteristic for larva, and is retained in subimagoes and imagoes (whose prothorax sclerotization is less distinct than in larva).

This structure has no direct correspondence with larval specialization: among Furcatergaliae, there are larvae with thorax either cylindrical (in many Fossoriae) or flattened (in many others), with fore legs non-specialized or highly specialized as burrowing (in Fossoriae).

Sometimes larval pleurites undergone further reduction and are immovably fused with tergite, so that fore legs are directly articulated with the tergite [see Campsurus/fg1 (3) below].

In majority of other mayflies pleurite is completely or largely exposed externally and retains distinct pleural suture (Kluge 2004: Fig.3:A). Pleurite structure similar to that of Furcatergaliae is found only in some Heptagennota (especially Heptagenia/f5=g4): their larvae, being flattened dorsoventrally, have prothorax flattened, with wide paranotal lobes, and pleurites are folded under them in a form of flat apodemes; sometimes these apodemes are narrowed, as in Furcatergaliae. Other mayfly larvae with distinctly flattened body or flattened ventral side either have normally developed external prothoracic pleurites (Discoglossata, Baetisca/f2=g1, Acanthametropus/fg1, Ametropus – Kluge 2004: Fig.25:B), or have pleurites hidden, but not in a form of so narrow apodemes (Prosopistoma/f1=g2).

(2) In imago and subimago on all legs 1st tarsal segment (fused with tibia) is strongly shortened, its length usually does not exceed its thickness (Kluge 2004: Fig.83:G). Other mayfly taxa the 1st tarsal segment is either long, or more or less shortened in selected species only.

In some representatives of Furcatergaliae tarsal structure is secondarily changed (see Index of characters [2.2.84]): rarely the 1st tarsal segment is secondarily separated from tibia (Kluge 2004: Fig.81:C), and/or secondarily elongate (Kluge 2004: Fig.86:G), and/or fused with the 2nd segment (Kluge 2004: Fig.98:A–B). Particularly, Machadorythus has unusually modified tarsi, which have 4 segments only, with the proximalmost segments long and fused with tibia (Kluge 2004: Fig.99:F), like that of Tetramerotarsata. In representatives with non-functional legs tarsi can have less number of segments, or lack segments, or are lost (see Index of characters [2.2.83]).

Characters of Furcatergaliae of unclear phylogenetic status.

(3) On imaginal and subimaginal mesothorax anterior paracoxal suture is incomplete: on ventral side of episternum it becomes shallow and indistinct, or absent, does not reach basisternum (Kluge 2004: Fig.68:D–E). Non-unique apomorphy, the same in Rallidens and many Heptagennota (see Index of characters [2.2.19]).

(4) On hind wing MA lost its bifurcation; thus, hind wing has maximum two primary triads – RS and MP, with a simple MA between them (Kluge 2004: Fig.68:B). Non-unique apomorphy (see Index of characters [2.2.67]). In Furcatergaliae, as well as in other groups of Ephemeroptera, hind wing can be strongly reduced or disappears completely, in this case this character loses its actuality. Rarely secondary triads can be added [see below, Vietnamella (4)].

(5) Tergalii are initially bifurcate or bilamellate, without marginal ribs (with this the name "Furcatergaliae" is connected). All or at least part of tergalii are bifurcate or bilamellate at least in primitive representatives of each subordinate taxon [see below, Fimbriatotergaliae (6), Ephemerella/fg1 (7) and Leptophlebia/fg1 (7)] (Kluge 2004: Fig.67:A, 82:E, 91:B–F). In some Furcatergaliae one of the two lamellae is secondarily lost, thus tergalius becomes single-lamellate. Costal and anal ribs are either lost (in majority of representatives), or located at a distance from costal and anal margins correspondingly (in some Fimbriatotergaliae and Pantricorythi only – see Index of characters [1.3.27] and [1.3.28]); thus tergalial margins are never armed with ribs.

Besides Furcatergaliae, tergalii independently got bilamellate structure in some other mayfly groups: in some Metretopus/fg1 – because of ventral curvation of costal lobe; in Siphlonurus/fg2 and some others – because of ventral curvation of anal lobe; in Tasmanophlebia/fg1 and some others – because of dorsal curvation of anal lobe; in Branchitergaliae and some others – because of development of secondary ventral fibrillose portion (see Index of characters [1.3.24]). Origin of bilamellate tergalial structure in Furcatergaliae is unclear. Possibly, this is a synapomorphy with Branchitergaliae [see Bidentiseta (2)].

(6) Larva lost primary swimming siphlonuroid specialization: legs are unable to stretch posteriorly, and caudalii have no siphlonuroid setation; at the same time ability to make dorsoventral abdominal movements is retained; in some taxa larva retains long abdomen able to make effective undulate movements; in others larval abdomen is shortened.

When larva swims, its legs are either folded under the body by knees directed posteriorly, or pressed to the body in a special manner [see Fossoriae (1) below].

Larval caudalii never have primitive siphlonuroid structure with swimming setae on paracercus and median sides of cerci only: either cerci have swimming setae both on median and lateral sides, or swimming setae are lost. Among Furcatergaliae, only Fossoriae retain difference between the secondary swimming setae on lateral sides of cerci and the primary swimming setae on median sides of cerci and lateral sides of paracercus; some of them also retain oblique boundaries of cercal segments. In other representatives swimming setae, if present, have equal structure and density on both lateral and median sides of cerci and lateral sides of paracercus. Such swimming setae are present in all Potamanthus/fg1, all Euthyplocia/fg1, some Caenotergaliae and some Ephemerella/fg1. In many representatives of Caenotergaliae, Ephemerella/fg1 and Leptophlebia/fg1 caudalii lack swimming setae at all (but can have whorls of long setae on segment boundaries).

Size. Fore wing length 2–40 mm.

Age and distribution. Late Jurassic (see Fossoriae INCERTAE SEDIS) – recent; world-wide.

Classifications of Furcatergaliae. Besides the accepted here division of Furcatergaliae into Fimbriatotergaliae, Ephemerella/fg1 and Leptophlebia/fg1, the following classifications are possible.

      

I. Taxon uniting Potamanthus/fg1 + Caenotergaliae + Ephemerella/fg1. In this case taxon Fimbriatotergaliae should not be recognized. Potamanthus/fg1, Caenotergaliae and Ephemerella/fg1 have the following common apomorphies.

(1) Tergalius I is vestigial, in a form of cylindrical sclerotized stick (instead of initial lamellate), covered with slender standing setae; it arises not from posterior-lateral angle of segment, but from a peculiar prominent cylindrical pedestal usually loca-ted far anteriad of hind margin of the segment (Kluge 2004: Fig.67:A, 82:B–C, 88:A, 91:G–H, 95:D–E). Unique apomorphy (see Index of characters [1.3.33]).

(2) In larva on dorsal (anterior) side of fore femur a transverse row of setae can be developed (Kluge 2004: Fig.89:H–J). Unique apomorphy (see Index of characters [1.2.29]).

(3) Larval mesonotum with a collar – transverse concave band on anterior margin, which is separated from the rest part of mesonotum by a transverse crest (Kluge 2004: Fig.67:B–C, 82:F, 88:B, 92:C–D) (see Index of characters [1.2.5]). The same crest separating the collar is present in some Euthyplocia/fg1 (distinct in inaccessibile [E.], nearly absent in Polyplocia examined); some Fossoriae have a concave transverse setose area at the same place.

(4) Egg can have one or two polar caps; anchors of the same structure are present in Potamanthus/fg1 and many Ephemerella/fg1 (see Index of characters [3.4]–[3.6]).

(5) Venation of cubital field of fore wing [see Anteritorna (1)] can be similar or even identical in certain specimens of Potamanthus/fg1, Neoephemera/fg1, Ephemerella/fg2, Vietnamella and Austremerella: proximalmost vein arising from CuA to wing margin is bifurcate (Kluge 2004: Fig.68:A, 81:A, 90:A, 95:A: x1 and x2); more distally from CuA can arise one or several bifurcate or simple veins more [see Potamanthus/fg1 (6), Caenotergaliae (9) and Ephemerella/fg1 (15)]. Similar venation occurs in some other taxa (see Index of characters [2.2.51]).

      

II. Taxon uniting Caenoptera + Tricoryptera. In the past this taxon was recognized as a "section 7 of the genera – type of Caenis" (Eaton 1883–1888: 137) or a family Brachycercidae (Lestage 1931a: 52, et al.).

From the one hand, Caenoptera are attributed to Caenotergaliae on the base of unique apomorphies in structure of tergalii [see Caenotergaliae (1)]; from the other hand, Tricoryptera are attributed to Ephemerella/fg1 on the base of a number of unique autapomorphies including that in tergalial structure [see Ephemerella/fg1 (1)–(8)]; from this, an assumption can be made that Caenoptera and Tricoryptera can not have close relationship. However, some characters in structure of imaginal pterothorax and wings, as well as in structure of larval caudalii, have deep similarity in Caenoptera and all or selected representatives of Tricoryptera. This similarity can not be explained as occasional coincidence or as adaptations for a similar mode of life. Both Caenoptera and Tricoryptera have small size, their adults can be shortly-moulting, actively flying, with mesothorax enlarged: In Caenoptera and Tricoryptera size ranges from 2 to 8–10 mm; representatives of other Caenotergaliae and Ephemerella/fg1 are usually larger, their size ranges from 5 to 20 mm. In Caenoptera proportion of mesonotum length / fore wing length is 0.4–0.5, in Tricoryptera – 0.3–0.4, in other mayflies it is usually less and ranges from 0.2 to 0.35.

Among Tricoryptera, the most similar to Caenoptera in imaginal characters is Tricorythodes attributed to Leptohyphes/fg1.

      

II.a. Apomorphies common for Caenoptera and all Tricoryptera. 

(1) Infrascutellum of mesothorax is interrupted medially, scutellum can be large with enlarged lateral impressions (Kluge 2004: Fig.66:A,C, 89:B). The same in Teloganodes/f1=g3 (see Index of characters [2.2.17]).

(2) On fore wing vein CuP is not connected with CuA and looks as arising from AA; cubital field with bifurcate vein iCu [see Caenoptera (10) and Tricoryptera (1)] (Kluge 2004: Fig.66:A,C).

     

II.b. Apomorphies common for Caenoptera and selected groups of Tricoryptera – Tricorygnatha and Leptohyphes/fg1.

(3) Sublateroscutum of mesothorax has a transverse interscutal suture (Kluge 2004: Fig.66:A,C, 87, 89, 102, 104) (see Index of characters [2.2.10]). This secondary suture has a form of sharp transverse furrow, separating the sublateroscutum (with areas of attachment of scuto-coxal muscles – S.CmA and S.CmP) from the posterior scutal protuberance (with area of attachment of the scuto-lateropostnotal muscle – S.LPNm). In other mayflies the sublateroscutum is separated from the posterior scutal protuberance by indistinct concavity only.

(4) Anterior paracoxal suture of mesothorax is transferred posteriorly, close to anterior margin of coxal conjunctiva, so that episternum is integral, consisting of anepisternum only (Kluge 2004: Fig.66:A,C). Non-unique apo-morphy (see Index of characters [2.2.19]).

(5) On fore wing [see (2)] marginal intercalaries are absent. Non-unique character (see Index of characters [2.2.55]).

(6) In imago amphitornal margin of wing with setae as in subimago. Non-unique, but rare apomorphy (see Index of characters [2.2.27]).

(7) Caudalii (cerci and paracercus) of male larva are thickened at proximal part, unlike caudalii of female larva, which have usual form (Kluge 2004: Fig.103:E–F) (see Index of characters [1.3.63]). Thickening of male larval caudalii is connected with their strong elongation in male imago: when larva is ready to moult to subimago, inside its thickened caudalius is located a crumpled anlage of adult caudalius. In other respects larval structure retains sharp difference from imaginal one. In other mayflies sexual dimorphism of caudalii is usually expressed in imagoes and subimagoes only, but not in larva; only in some Fossoriae, whose larval abdomen has imaginal features (such as developed genitals), larval caudalii have sexual dimorphism similar to that of Caenoptera and Tricoryptera.

(8) Adults are shortly-moulting but not short-living (see Index of characters [2]).

     

II.c. Apomorphies common for Caenoptera and Tricorythodes only.

(9) In imago and subimago scuto-lateropostnotal muscle (S.LPNm) is strongly enlarged; in connection with this, lateropostnotum is also strongly enlarged, fused with epimeron and reaches coxal conjunctiva (Kluge 2004: Fig.66:A,C, 87, 104). Unique apomorphy (see Index of characters [2.2.16]).

(10) Metathorax is strongly reduced; hind wings are lost in both sexes (the same in Tricorygnatha and some others); in female metathoracic wing muscles, including scuto-episternal muscle (S.ESm) and median tergal muscle (MTm), are lost (see Index of characters [2.2.26]). Unique apomorphy; in other mayflies, even if hind wings are completely lost, in metathorax S.ESm and MTm are retained in both sexes.

(11) Mesonotal suture is lost (Kluge 2004: Fig.66:A,C). In different mayflies mesonotal suture disappears by different ways (see Index of characters [2.2.8]). In Tricorythodes mesonotal suture initially was transverse [see Ephemerella/fg1 (9)] and than smoothed; about this testifies the fact that in different representatives of Tricoryptera mesonotal suture is expressed in different degree. Caenoptera have no traces of mesonotal suture; if proceed from the assumption about relationship of Caenoptera and Neoephemera/fg1, we should assume that in Caenoptera the mesonotal suture disappeared because was stretched posteriorly at each side and fused with median and lateroparapsidal sutures [see Neoephemera/fg1 (5)]. In this case absence of mesonotal suture in Tricorythodes and Caenoptera is not their common character.

(12) Female imaginal and subimaginal caudalii are strongly diminished [see Caenoptera (6) and Tricorythodes (6)].

     

III. Lanceolata = Potamanthus/fg1 + Euthyplocia/fg1 + Fossoriae + Leptophlebia/fg1. In this case the taxon Fimbriatotergaliae is not recognized. The taxon Lanceolata McCafferty 1991 united Potamanthus/fg1, Euthyplocia/fg1, Fossoriae and

Leptophlebia/fg1 and was characterized by a single character – elongate double tergalii. Probably this is a plesiomorphy among Furcatergaliae [see Furcatergaliae (5)].

      

IV. Taxon uniting Caenotergaliae + Ephemerella/fg1. Some authors unite Caenotergaliae and Ephemerella/fg1 in a taxon called Pannota auct. (non Pannota McCafferty & Edmunds 1979). Actually Caenotergaliae and Ephemerella/fg1 have a number of common characters, but no one of them is characteristic for these two taxa only (Kluge 2004: Table 5).
Here we divide the taxon Furcatergaliae (or Ephemera/fg6) into:

1. Fimbriatotergaliae (or Ephemera/fg7)

1.1. Potamanthus/fg1

1.2. Euthyplocia/fg1

1.3. Fossoriae, or Ephemera/fg8

1.3.1. Ichthybotus

1.3.2. Ephemera/fg9

1.3.3. Behningia/fg1

1.3.4. Cryptoprosternata, or Palingenia/f1=Ephoron/g1

1.4. Caenotergaliae, or Caenis/f1=Brachycercus/g1

1.4.1. Neoephemera/fg1

1.4.2. Caenoptera, or Caenis/f2=Brachycercus/g2

2. Ephemerella/fg1

2.1. Ephemerella/fg2

2.2. Pantricorythi, or Tricorythus/fg1

3. Leptophlebia/fg1

Some fossil taxa have uncertain systematic position