CLADOENDESIS OF EPHEMEROPTERA

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 (1) Labrum is widened in distal part, thickened in proximal part; ventrally with sclerotized lateral margins (Kluge & Bernal 2018: Fig.74); on its dorsal surface, number of long setae in the pair of antero-lateral rows is increased, these rows nearly meet the submedian pair of long setae, so that all these long setae form nearly integral transverse row (Kluge & Bernal 2018: Fig.71). Such a labral structure is found in some other taxa.

(2) Incisor of each mandible is blade-like, i.e. greatly elongated (several times longer than kinetodontium), straight, with denticles diminished or lost (Kluge & Bernal 2018: Fig.18–21, 79–82). Incisors are often broken (Kluge & Bernal 2018: Fig.16–17, 77–78), so their initial shape should be observed either on freshly-moulted specimens, or inside old mandible just before moulting. Besides Moribaetis, similar blade-like mandibular incisors independently evolved in some other distantly related baetid taxa.

(3) Prostheca of right mandible is slender, straight, directed parallel to incisor, pointed or terminated by few slender processes (Kluge & Bernal 2018: Fig.21, 82); this is one of the types of right prostheca, which are repeated among Baetidae. Prostheca of left mandible varies from the form usual for Baetidae (in latipennis [Moribaetis] – Fig.80) to similar to right prostheca (in M. maculipennis [Baetis] – Fig.19).

(4) Maxilla of the «Baetis-type», i.e. with 1st dentiseta canine-like, heavily sclerotized and bent toward canines (Kluge & Bernal 2018: Fig.83; Flowers 1979: fig.9, Waltz & McCafferty 1985: fig.28, 37). The same in many other non-related baetid taxa.

(5) Labium has peculiar structure and differs from other taxa by shape of paraglossa and one seta instead of the dorso-median row (Kluge & Bernal 2018: Fig.22, 76). Paraglossa is sharply narrowing toward apex; its long latero-apical setae are sparse on lateral margin and compactly concentrated on extreme apex of paraglossa, forming here 3 rows; ventro-median setal row is completely absent; dorso-median row is reduced to a single long seta (Fig.22: d-m). Glossa is long and narrow, its dorso-lateral row is reduced to a few setae on lateral margin near apex.

Formerly paraglossae of maculipennis [Baetis] and the larva ascribed to salvini [Baetis] were erroneously described as having only 2 rows of apical setae (Flowers 1979: 190, fig. 10; Waltz & McCafferty 1985: 246, 247, 250); actually they have 3 rows.

(6) Larval prothorax with a pair of tracheal gills, each representing a short and simple (non-branched) outgrowth arising from the membrane connecting prosternum with coxal bases (Waltz & McCafferty 1985: fig. 31). These outgrows were termed «osmobranchia» (Waltz & McCafferty 1985), but actually they represent true tracheal gills, because they are supplied with special tracheae: just proximad of coxal base, the leg trachea has a thick branch which passes into the gill (Kluge & Bernal 2018: Fig.85–86). In contrast to prothorax, mesothorax and metathorax have no gills, and their leg tracheae have no such branches. While the trachea passing into the gill is rather thick, it is unclear if these gills can play any role in respiration because they are very small in relation to the body size and in relation to tergalii, which are large, well-tracheated (Kluge & Bernal 2018: Fig.5–11) and also serve as tracheal gills. Larvae inhabit places with the fastest water current, where the role of any gills is likely minimal.

(7) Larval legs are differentiated so that fore, middle and hind legs have the following differences in proportions and setation (Kluge & Bernal 2018: Fig.25–27, 89–91):

Fore, middle and hind femora slightly differ in length, with fore femur being the shortest and hind femur being the longest; fore and middle tibia are of equal length, while hind tibia is 1.2 times shorter; fore, middle and hind tarsi slightly differ in length, with fore tarsus being the longest and hind tarsus being the shortest. Thus, on fore leg tibia and tarsus combined are 1.3 times longer than femur, while on hind leg tibia and tarsus combined are subequal to femur or only 1.1 times longer. In course of development to subimago and to imago, legs become significantly longer, and their proportions are changed, but hind tibia and tarsus continue to be shorter than middle ones.

Fore femur is the thickest; short spine-like setae on inner side of femur (Kluge & Bernal 2018: Figs.33, 95) occupy widest area on fore femur, narrower area on middle femur and narrowest area on hind femur. Apices of fore and middle femora with dense bunch of 4–9 spine-like setae of the same structure as spine-like setae of the longitudinal row on outer side [see (8)] (Kluge & Bernal 2018: Fig. 92–93); apex of hind femur usually with two such setae (Kluge & Bernal 2018: Fig.94) (as on all femora of many other Turbanoculata).

(8) Larval legs with stout pointed spine-like setae, fine setae and scales in angulated bases [similar to scales of abdomen – see (13)]. Each femur [different on different leg pairs – see (7)] on outer side bears a regular sparse row of stout pointed spine-like setae; between them stretches an interrupted irregular row of fine setae (Kluge & Bernal 2018: Fig.92). Apex of each femur with smaller spine-like setae (Kluge & Bernal 2018: Fig.92–94). Each tibia with row of small pointed spine-like setae on outer side (Kluge & Bernal 2018: Fig.92) and with irregular spine-like setae on inner side.

(9) Patella-tibial suture is modified as the following: on each larval leg it stretches longitudinally and gradually disappears not reaching inner (ventral) side of tibia (Kluge & Bernal 2018: Fig.25–27, 89–91). On middle and hind legs of subimago and imago patella-tibial suture reaches inner side of tibia (Kluge & Bernal 2018: Fig.30,32), but on fore leg of female subimago and imago (known only for maculipennis [Baetis]) patella-tibial suture stretches longitudinally and does not reach inner side of tibia (Kluge & Bernal 2018: Fig.28), sometimes being shortened and vestigial (Kluge & Bernal 2018: Fig. 29,31) (male subimago and imago have no patella-tibial suture on fore legs, as in other Ephemeroptera). In this respect Moribaetis somewhat resembles the basal plesiomorphon Protopatellata, which in all stages of both sexes have patella-tibial suture only on middle and hind legs, but not on fore legs. 

(10) In subimagoes of both sexes, all tarsal segments on all legs are entirely covered with blunt microlepides only. The same in some other Baetungulata-non-Baetofemorata and in all Baetofemorata.

(11) Larval claw bears a large seta on posterior side; this seta located equidistantly with the most distal denticle of the claw; base of this seta is inserted into a cylindrical canal (Kluge & Bernal 2018: Fig.23–24, 87). Individual claws of latipennis [Moribaetis] have two such setae (Kluge & Bernal 2018: Fig.88) (sometimes three, according to Waltz & McCafferty 1985).

(12) Hind wing is relatively wide, with short, slightly hooked costal projection and 3 longitudinal veins, among which 2nd vein is symmetrically bifurcated, with intercalary between its branches; sometimes additional intercalary(es) and cross vein(s) are present (Kluge & Bernal 2018: Fig.55). Larval protopteron has corresponding form and venation (Kluge & Bernal 2018: Fig.67).

(13) Larval abdominal terga and sterna with numerous short scales in operculate sockets (Kluge & Bernal 2018: Fig.70). Similar scales are present on thoracic pleura and on legs. Such kind of scale sockets with two operculae is probably initial for Turbanoculata [see Turbanoculata (12)].

(14) Larval abdominal terga with long and pointed denticles on posterior margins; in both species denticles are absent on tergum I and present on terga II–X; on tergum IX row of denticles is interrupted behind pair of submedian setae (Kluge & Bernal 2018: Fig.70). Abdominal sterna with smaller pointed denticles, which are present either on sterna V–IX (in maculipennis [Baetis]), or only on sterna VIII–IX (in latipennis [Moribaetis]).

(15) Tergalii (unable to make respiratory movements, as in other Baetungulata) have the following structure. Tergalii I more or less diminished, with costal and anal ribs very short. Tergalii II–VII with costal rib well-developed and anal rib rather short, so that a long part of hind margin is free of rib; costal rib with serration (Kluge & Bernal 2018: Fig.5–11).

(16) Larval paracercus is well-developed, cerci greatly elongated, longer than body (Kluge & Bernal 2018: Fig.1–2, 62); both cerci and paracercus bear very dense primary swimming setae, which are present on most their segments; bases of these setae are pressed together and regularly alternate as shifted dorsally and ventrally from the common line (Kluge & Bernal 2018: Fig.14). Segments of cerci are cylindrical, with boundaries not inclined and with denticles on posterior margin not enlarged on any side of cerci or paracercus; secondary swimming setae are absent (Kluge & Bernal 2018: Fig.63).

(17) Gonostyli have unusual shape and paradoxical development: in definitive condition 1st segment is longer than 2nd segment (Kluge & Bernal 2018: Fig.39, 47); in course of development, 2nd segment grows earlier, so in subimago 1st segment is much shorter than 2nd (Kluge & Bernal 2018: Fig.37, 46); in mature larva developing subimaginal gonostyli are folded under larval cuticle in a peculiar manner, which can be termed «Moribaetis-type». When subimaginal wings are already fully developed and crumpled under cuticle of protopteron, developing subimaginal gonostylus has 1st segment extremely short, and 2nd segment forming a loop (3rd segment indistinguishable at this stage); apex of gonostylus locates inside apex of larval protogonostylus (Kluge & Bernal 2018: Fig.36, 44). Just before moult, gonostyli elongate and meet medially by their loops of 2nd segments (Kluge & Bernal 2018: Fig.45). This «Moribaetis-type» of gonostyli folding proceed from the «Nigrobaetis-type» [at which 2nd segment is directed caudally and bent with convexity directed medially – see Baetovectata (3)]: in Moribaetis 2nd segment is longer and its bent is transformed to a loop (see Index of characters [2.3.9]).

Other peculiar features of genitals are the following: sterno-styligeral muscle is unusually short, so that originates far from fore margin of abdominal sternum IX; a pair of protuberances is present between unistyligers; 3rd segment of gonostylus is very short (Kluge & Bernal 2018: Fig.47).

Gonostyli have colourless cuticle and brown hypodermal coloration; their hypodermal coloration varies individually, being developed first of all in distal part of 1st segment, in distal part of 2nd segment and in small 3rd segment. This hypodermal coloration appears in last larval instar (Kluge & Bernal 2018: Fig.36, 44), that helps to reveal homology of segments at different stages of development (Kluge & Bernal 2018: Fig.36–39, 44–47).

All these features of genital structure in larval, subimaginal and imaginal stages are examined for maculipennis [Baetis], while genitals of latipennis [Moribaetis] were examined for a single specimen of imago, which have not shed subimaginal cuticle. Genitals of this specimen (Kluge & Bernal 2018: Fig.101) have following features the same as in maculipennis [Baetis]: pair of protuberances between unistyligers; subimaginal gonostyli with sharply curved 2nd segments and very short 3rd segment; inside them coloured imaginal gonostyli with 1st segments strongly crumpled; the same shape of gonovectes; the same unusually short sterno-styligeral muscle.

(18) Coloration is similar in both examined species and has the following features: 
Hypodermal coloration (which is present independently of moults and passes from larva to subimago and to imago) consists of peculiar contrasting brown markings on thorax (Kluge & Bernal 2018: Fig.3), abdomen and legs. On abdominal terga it includes paired submedian stripes, usually well developed on uromeres III–IV and VI–VIII; shape of these stripes is somewhat different in M. maculipennis and M. latipennis sp. n. (see species characteristics below). Hypodermal coloration of legs consists of two brow or reddish spots on posterior side of femur, one at middle and another near apex (Kluge & Bernal 2018: Fig. 50, 54, 62). In contrast to hypodermal coloration of trunk and legs, hypodermal coloration of imaginal cerci appears only at the end of last larval instar, when subimaginal cerci grow under larval cuticle (Kluge & Bernal 2018: Fig.40).

Cuticular pigmentation of larva (present only in larval stage and becoming most intensive at the end of each larval instar) consists of diffusive brown and colourless areas on head, thorax, legs and abdomen (Kluge & Bernal 2018: Fig.4, 64–66). General coloration of larva is determined by combination of these cuticular and hypodermal pigments. Abdominal segments IX and X usually have both cuticular and hypodermal coloration poorly developed or absent, so tip of abdomen is often contrastingly light (Kluge & Bernal 2018: Fig.1–2, 62).

Subimaginal cuticular coloration is the following: pronotum is light brown; mesonotum is light brown with certain sutures darker brown (Kluge & Bernal 2018: Fig.52); thoracic pleura have light and dark brown areas (Kluge & Bernal 2018: Fig.51); wings are dark brown due to dark brown ring at base of each microtrichion, veins lack this coloration (Kluge & Bernal 2018: Fig.98); legs are unicolorous, nearly colourless, with dark brown marks at base of tibia (Kluge & Bernal 2018: Fig.31–32); abdominal terga are uniformly light brown, sterna much lighter.

Imaginal wings have membrane with contrasting brown marking on colourless background; in all three species these markings border cross veins and are present also in proximal parts of costal and subcostal fields, where cross veins are absent (Kluge & Bernal 2018: Fig.48–50, 53–54, 100, 102). At least in maculipennis [Baetis] and latipennis [Moribaetis] this wing pigmentation appears in course of subimaginal development: just after moult from larva to subimago, wings are uniformly grey due to coloration of subimaginal cuticle (Kluge & Bernal 2018: Fig.34–35); before moult from subimago to imago, wings get imaginal markings visible through dark subimaginal cuticle (Kluge & Bernal 2018: Fig.96–97).
 

Autapomorphies of Moribaetis.

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Characters of Moribaetis of unclear phylogenetic status. 

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Plesiomorphies of Moribaetis.

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