CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphy of Cheleocloeon.

(1) Genitals of male imago have peculiar structure of gonovectes (Kluge 2016: Figs 98, 99–102, 104–106, 108,110). Gonovectes are movable, wide, well-sclerotized and pigmented, with distal margin strengthened; apex of each gonovectis (where gonoduct is attached), being directed medially, is pointed and hooked so that its point is directed cranially (i.e. into the body). Protuberance at mid-length of gonovectis, served for attachment of gonovectal muscle, is prominent, located at the same plane as the hooked apex and has the same direction (cranially, i.e., into the body) (Kluge 2016: Fig. 101). When gonovectes are turned caudally, their hooked apices are visible between unistyligers (Kluge 2016: Figs 99, 106); when they are turned cranially, they are invisible from ventral view (Kluge 2016: Fig. 105). Penial bridge is slightly sclerotized in lateral parts and membranous medially (Kluge 2016: Figs 101, 104). This structure of gonovectes and penial bridge is uniform in all species examined (Ch. clavifolium, Ch. lancetofolium, Ch. truncifolium and Ch. sp.1). Unpaired styligeral muscle is well developed, so that unistyligers can be brought together (Kluge 2016: Fig. 105) and turned apart (Kluge 2016: Fig. 106). Median sclerite served for insertion of the styligeral muscle, is either present (Kluge 2016: Fig. 110), or not (such sclerite occurs also in some Protopatellata). Bases of unistyligers are either contiguous (Kluge 2016: Figs 106, 108), or narrowly separated (Kluge 2016: Fig. 98), but never widely separated. Gonostylus has 2nd segment widened apically and 3rd segment small and clavate (this is similar to Cloeon/fg1, Centroptilum and Anafroptilum). Shape of 1st segment of gonostylus is species-specific; in certain species (Ch. clavifolium and Ch. soldani) it has a sclerotized and pigmented concavity on median side close to the base (Kluge 2016: Figs 99-100, 104-106; Gattolliat & Sartori 2008: Fig. 7).

Genitals of the type species, Ch. yolandae, have not been examined by me, and structure of their internal parts (gonovectes and penial bridge) is not described; shape of their external parts (gonostyli and unistyligers) well agree with the description given above (Wuillot & Gillies 1993: Fig. 2).

Structure of gonovectes is unique for Cheleocloeon, not found in any other taxa. In all Cloeon/fg1, Baetopus and Anafroptilum, gonovectes are immovably fused by their apices with penial bridge (e.g., Kluge 2012: Fig. 45; Kluge, Tiunova & Novikova 2014: Figs 30-31). In Centroptilum gonovectes are movable, pointed and hooked; in contrast to Cheleocloeon, their points are directed not cranially, but caudally (Grandi 1960: Fig. XI.3). In Afrobaetodes gonovectes are also movable and hooked; in contrast to Cheleocloeon, the protuberance which serves for muscle attachment and the hooked apex are directed to opposite sides (unpublished data). In all Baetovectata gonovectes are also movable, but slender, sharply bent and deeply evaginated into the body. In various taxa of Protopatellata, gonovectes are either fused with penial bridge (e.g. in Rhithrocloeon/fg1, Indocloeon and others) or movable, but always different from that of Cheleocloeon.

Plesiomorphies and characters of  Cheleocloeon of unclear phylogenetic status.

(2) Larval frons. Bases of antennae are widely separated, frons between them is flat (Kluge 2016: Fig.9) (unlike carinate in some other taxa).

(3) Larval frontal suture. Frontal suture is nearly semicircular, with angle blunt and arms evenly arched (Kluge 2016: Fig.9).

(4) Labrum. Labrum has an usual form, outer surface with submedian pair of long setae and a few (often two) antero-lateral setae on each side (Kluge 2016: Fig.1; Gattolliat et al. 2009: Figs 1–3, 35); in some individuals these setae are absent. Smaller setae are irregularly scattered of outer surface of labrum; some of them can be subequal to the submedian and antero-lateral setae. Therefore the structure of the labrum is not a good diagnostic character for Cheleocloeon, but it allows to be distinguished from that taxa, whose antero-lateral setae form regular rows.

(5) Mandibles (Kluge 2016: Figs 7-8, 16-18, 58-59; Wuillot & Gillies 1993: Figs 4, 5, 13, 14; Gattolliat et al. 2009: Figs 7–9, 13–15). On both mandibles, incisor and kinetodontium are moderately fused together. Left incisor is terminated by 3 prominent denticles with distal denticle the longest, without small ventral distal denticle. Left kinetodontium has 1st (most distal) denticle the longest, 2nd denticle shorter than 3rd denticle. Left prostheca is terminated by 3–4 stout short denticles and 2–3 slender longer denticles (individual variability). Right incisor is terminated by 4 prominent denticles, with or without a small ventral distal denticle. Right kinetodontium is terminated by 4 denticles gradually getting shorter from most distal to most proximal. Right prostheca is stick-like, directed medially, apically either narrowed, or widened (species-specific character). Margin between prostheca and mola bears dense setae-like processes.

(6) Maxillae (Kluge 2016: Figs 2-3). Maxilla of the «Cloeon-type», i.e. with long slender canines and dentisetae; 1st dentiseta is simple, 2nd and 3rd dentisetae are bifid; 1st and 2nd dentisetae are pressed to canines, 3rd dentiseta is separated. Medio-dorsal setal row, continued proximad of dentisetae, consists of 4–6 setae, which are either all simple, or some of them are bifid (individual variability); in some individuals the first seta of this row, being adjacent to the 3rd dentiseta, is bifid, thicker than others and resembles dentiseta, so that maxilla appears to have 4 dentisetae (while only 3 true dentisetae are present).

(7) Maxillary palp. Maxillary palp is 2-segmented, with 2nd segment often arched (Kluge 2016: Fig.2).

(8) Labium (Kluge 2016: Figs 4–6). Labium of the «Cloeon-type», i.e., glossa and paraglossa have subequal width and length, paraglossa is crescent-shaped. Glossa has the following setal rows: median row (regular row of spine-like setae along median margin); dorso-lateral row (regular row along lateral margin, with setal bases visible in dorsal view). Ventral side of glossa bears setae directed ventrally; they are located irregularly in the proximal part of the glossa and form a ventro-median row (sparse row parallel to median margin). The median, the dorso-lateral and the ventro-medial rows stretch along most of the length of the glossa.

Paraglossa has following setation: latero-apical setae (longest ones) form a regular sparse row along lateral and apical margin and irregularly located on the dorsal side; ventro-median row (regular row of long slender straight setae attached on ventral side and directed mainly medially); dorso-median row (regular row of thicker seta attached on dorsal side and directed medially-distally). The ventro-median and the dorso-median rows are stretched along most of the length of the paraglossa.

Similar labial structure occurs in some other baetid taxa, both among Protopatellata and Anteropatellata (e.g., most Cloeon/fg1, Centroptilum, Anafroptilum).

(9) Labial palp (Kluge 2016: Figs 4-5). Shape of the labial palp is characteristic for Cheleocloeon: 2nd segment has prominent disto-median projection with distal margin convex. 2nd segment retains muscle running from its base to base of 3rd segment (shown by dotted stripe on figures by Wuillot and Gillies (1993: Figs 6, 15). Two forms of labial palp are distinguishable among Cheleocloeon: (1) with apex of projection of 2nd segment pointed (in Ch. yolandae, Ch. carinatum, Ch. littorale and Ch. sp.3) (Wuillot & Gillies 1993: Figs 6, 15) and (2) rounded (in other species—Ch. clavifolium, Ch. lancetofolium, Ch. truncifolium, Ch. madagascariense, Ch. dimorphicum, Ch. excisum, Ch. soldani and Ch. sp.2) (Kluge 2016: Figs 4-5). Some non-related taxa also have disto-median projections of 2nd segment of maxillary palp, but its shape is often different from that of Cheleocloeon.

(10) Postsubalar sclerite (Kluge 2016: Figs 89, 92). Postsubalare (which is present in imago and subimago and in both these stages has contrasting brown cuticular coloration) has posterior-dorsal corner stretched to a rather wide process with shallowly convex dorsal margin. This is different from Cloeon/fg1 and some other taxa, whose posterior-dorsal postsubalare process is small or narrow, with concave dorsal margin.

(11) Larval leg setation (Kluge 2016: Figs 21, 25, 26). Outer side of femur bears sparse row of small stout setae, apically terminated by 2 small stout setae located close together. The same in many other baetid taxa; possible plesiomorphy.

While setation of legs is rather uniform among Cheleocloeon, leg shape varies from slender, with femur parallel-sided (Kluge 2016: Fig. 21) to rather stout, with femur thickened (Kluge 2016: Fig. 26).

(12) Patella-tibial suture (Kluge 2016: Figs 19-22, 25-26). This suture is equally developed on all legs of larva of both sexes and on all legs of female subimago and imago, being absent only on fore legs of male subimago and imago (i.e., it has the condition typical for Anteropatellata).

This character is important here, because Cheleocloeon was confused with both some Anteropatellata (e.g., Centroptilum) and with some Protopatellata (e.g., Afroptilum and Bugilliesia). M.T. Gillies wrote that Cheleocloeon has patella-tibial suture on middle and hind leg only (Gillies 2001: 32); this conclusion was based on sigiense [Cheleocloeon], which does not belong to Cheleocloeon. Gattolliat et al. (2009) wrote in the larval diagnosis of Cheleocloeon, that the patella-tibial suture is absent. Probably, this statement was caused by the fact that larval legs of Cheleocloeon have colorless translucent cuticle, so the patella-tibial suture can be poorly visible on a background of living tissues; it is well visible on empty larval exuviae. The anteropatellate condition of patella-tibial suture is present in all species examined.

Ch. yolandae and Ch. carinatum. When Wuillot and Gillies (1993) described these species, they did not know about this character and did not pay special attention to it. Distal border of dark macula, shown by dots on fore legs of both these species (Wuillot & Gillies 1993: Figs 8, 17) correspond to the patella-tibial suture. According to my examination of larval exuviae from Zambia, in both species patella-tibial suture is present on all legs; female subimago and imago of Ch. yolandae also have patella-tibial suture equally developed on all legs (Kluge 2016: Figs 19–22).

Ch. excisum. In the previous descriptions (Barnard 1932; Lugo-Ortiz & McCafferty 1997a) patella-tibial suture was not mentioned; actually it is equally developed on all legs of larva (as in Kluge 2016: Fig. 25).

Ch. soldani. According to the original description, “tibio-patellar suture absent” (Gattolliat & Sartori 2008: 52). Actually this suture is equally developed on all legs of larva (Kluge 2016: Fig. 25).

All other examined species, Ch. clavifolium, Ch. lancetofolium, Ch. truncifolium and larvae of unnamed species have patella-tibial suture equally developed on all legs of larva and equally developed on all legs of female subimago and imago (Kluge 2016: Fig. 26).

(13) Imaginal and subimaginal tarsi. Tarsus of middle and hind leg is relatively long, about 0.7–0.9 of tibia length; proximal tarsal segment (result of complete fusion of primary 1st+2nd tarsomeres) is much longer than others, about 0.4–0.5 of total tarsal length. All examined species have 2 apical spines on middle and hind legs of both sexes and on fore leg of female (on 2nd and 3rd primary tarsomeres).

(14) Microlepides on subimaginal tarsi. All tarsal segments of all legs of both sexes are covered by pointed microlepides (examined for both sexes of Ch. clavifolium, Ch. lancetofolium and Ch. truncifolium, males of Ch. soldani and Ch. sp. 1, females of Ch. yolandae and Ch. sp. 2). The same in Protopatellata, Cloeonini, Centroptilum, Baetopus, Afrobaetodes and some Baetovectata; in contrast to this, in some Baetovectata tarsi are partly or completely covered by blunt microlepides (Kluge & Novikova 2014: Figs 11–17). Such character pattern testifies that this is a plesiomorphy of Cheleocloeon.

(15) Larval claw (Kluge 2016: Figs 23-24, 27-29). Claw is slender, slightly bent, with 2 rows of denticles, among which minute denticles are located close to base of claw and larger denticles, if present, occupy more distal part of claw. In some species only minute proximal denticles are present. Larger denticles can be either well-expressed, or very delicate, thin-walled, translucent and poorly visible; they can be absent on individual claws. This is true for all species of Cheleocloeon (Gattolliat & Sartori 2008: 52).

Ch. yolandae. In the generic diagnosis of Cheleocloeon, based on two species, Ch. yolandae and Ch. carinatum, Wuillot and Gillies (1993) wrote that “claws long with minute teeth at base”. Actually, on the larval exuviae of Ch. yolandae examined by me, all six claws have, besides two rows of minute denticles near base, 2+2 larger denticles (Kluge 2016: Fig. 23); they are so delicate and translucent, that they can be easily overlooked.

Ch. carinatum. On the larval exuviae of Ch. carinatum examined, only minute denticles are present, larger denticles are absent.

Ch. excisum. In the descriptions and figures of Ch. excisum by Barnard (1932: 226, Fig. 15k) and Lugo-Ortiz & McCafferty (1997a: 286, Fig. 9), the claws are described as “with three to four poorly developed denticles”. Actually each claw has two rows of denticles, each row consists of minute denticles proximally and 4–7 larger denticles more distally (similar to Kluge 2016: Fig. 24).

Ch. soldani. According to the original description, claw “with one row of 6 reduced teeth proximally and 7 stout teeth apically” (Gattolliat & Sartori 2008: 52). Actually it has two equal rows of such denticles (Kluge 2016: Fig. 24).

Ch. clavifolium, Ch. lancetofolium and Ch. truncifolium sp.n. have at least two rows of minute denticles near base of claw (Kluge 2016: Figs 27–29).

(16) Hind wing (Kluge 2016: Figs 10, 11–13, 109, 112). Hind wing, if present, is of the «Centroptilum-type»: narrow, with 2 longitudinal veins only, with hooked costal projection (Kluge 2016: Fig. 11); larval hind protopteron is narrow, slightly S-bent, narrowed toward apex (Kluge 2016: Fig. 10). Females never have hind wings; males either have them, or not.

Ch. clavifolium, Ch. lancetofolium and Ch. truncifolium have hind wings in male; their female imagoes have vestiges of hind wings, which represent very small immovable membranous projections, whose length is equal to length of vestige of larval protopteron (Kluge 2016: Fig. 13); vestige of larval protopteron is rather wide and projected posteriad of posterior margin of metanotum (Kluge 2016: Fig. 12). The same vestiges of larval protopteron are present in female larvae of Ch. excisum, Ch. soldani, Ch. sp. 2 and Ch. sp. 3.

Ch. dimorphicum, according to the original description, also has hind wings in male, but its female imago has no vestiges of hind wings, and larval protoptera are “absent or considerably reduced, empty and rudimentary” (Soldán 1985: 182, Fig. 10).

Ch. yolandae and Ch. carinatum have no hind wings in male; at least females have no any vestiges of hind protoptera.

Contrary to the statement that females of Cheleocloeon never have developed hind wings, two species with hind wings in the female were attributed to Cheleocloeon. One of them, falcatum [Centroptilum], is known from imagoes only, and does not belong to Cheleocloeon. Another species, mirandei [Cheleocloeon] is known as a single female larva; recently it was moved to Bugilliesia (Gattolliat et al. 2009).

(17) Denticles on larval abdomen. Posterior margins of abdominal terga (at least terga II–X) bear pointed denticles, which can be larger (Kluge 2016: Fig. 62) or smaller. In Ch. carinatum, whose abdominal terga bear unpaired projections, these denticles border the margin of each projection (Kluge 2016: Fig. 70). Posterolateral spines are absent on all abdominal segments (as in most Baetidae). Lateral margins of all abdominal segments have no denticles (in contrast to Cloeon/fg1 and Anafroptilum). Posterior margin of tenth abdominal tergum is semicircular with even denticles, as on previous terga (lateral denticles are not enlarged, in contrast to Procloeon). Paraprocts bear pointed denticles (Kluge 2016: Fig. 14).

(18) Scales of larval abdomen. Abdominal terga, sterna and caudalii bear translucent scales; socket of such scale is W-shaped, i.e. with two concavities; each concavity is covered by a short cover, which is not projected distad of the concavity (Kluge 2016: Figs 15, 62-63). Scales with two covers are present in various taxa of Baetidae, but not in Cloeon/fg1, Centroptilum or Anafroptilum.

(19) Setae of larval abdomen. Abdominal terga and sterna, besides scales [see (18)] have only sparse, irregularly situated simple setae, which do not form rows or groups (Kluge 2016: Fig. 63).

(20) Structure of tergalii (Kluge 2016: Figs 30–57). Costal and anal ribs can be rather long, but not reaching apex of tergalius, so that distal margin of tergalius is not bordered by rib. First tergalius is narrower than others, more or less petiolate and paddle-shaped (see Index of characters [1.3.33]); its length can be either less, or equal, or greater than length of other tergalii.

(21) Mobility of tergalii. Tergalii are able to make rhythmical respiratory movements (see Index of characters [1.3.30]). Wuillot and Gillies (1993) wrote about Ch. yolandae and/or Ch. carinatum: “In living nymphs, while at rest, the first gill is held above the body like a banner and actively vibrated. In contrast, the remaining gills are held passively, close to the abdomen”. Actually other tergalii are also able to make respiratory vibration. I observed respiratory vibrations of Ch. yolandae, Ch. excisum, Ch. clavifolium and Ch. lancetofolium.

(22) Larval caudalii (Kluge 2016: Figs 60-61, 65, 68, 75, 80, 83). Paracercus is always as long as cerci; cerci and paracercus up to the apex bear well developed primary swimming setae. Each swimming seta is thick and sometimes darkened in proximal part and contrastingly thinner and always colorless in distal part. Distal part of each cercus bears sparse longitudinal row of delicate secondary swimming setae (Kluge 2016: Fig. 61). These features are not reported in literature, but observed by me for Ch. yolandae, Ch. carinatum, Ch. clavifolium. Ch. lancetofolium, Ch. excisum, Ch. soldani, Ch. sp.2 and Ch. sp.3.

Position of denticles on posterior margins of segments of caudalii have species-specific variability: In most species (Ch. clavifolium, Ch. lancetofolium, Ch. truncifolium, Ch. excisum, Ch. soldani, Ch. sp.2 and Ch. sp.3) enlarged pointed denticles form short transverse rows on each 4th or each 2nd segment on lateral side of each cercus (Kluge 2016: Fig. 60) and on dorsal side of paracercus, occasionally also on ventral side of paracercus. In Ch. yolandae such denticles are present only on cerci (one individual examined); in Ch. carinatum large denticles are absent (one individual examined).

(23) Pose of developing gonostyli (Kluge 2016: Figs 95, 96). Pose of developing subimaginal gonostyli folded under larval cuticle is of the «Cloeon-type», i.e. with 2nd segments diverging laterally. This is a plesiomorphic character, common with most Protopatellata, Cloeon/fg1, Centroptilum, Baetopus and Afrobaetodes; but it allows Cheleocloeon to be distinguished from Bugilliesia and other Rhithrocloeon/fg1, whose gonostyli have a quite different pose (Kluge 2016: Kluge 2012b, 2015). The pose of developing gonostyli is examined for Ch. excisum, Ch. soldani, Ch. clavifolium, Ch. lancetofolium, Ch. truncifolium and Ch. sp.2.

(24) Eggs (Kluge 2016: Figs 122-127, 128-133). Eggs are oval, with more or less expressed convex net-like relief, somewhat different in different species.