CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Crassabwa/g2.

(1) Structure of tergalii. Tergalius I with anal margin not bordered by rib and convex in proximal part; in larva of last instar this convex proximal portion is overturned and bent ventrally (Kluge et al. 2017: Fig.23-24, 84-85). In previous larval instars tergalius I is not folded in such a manner, being spread. Among examined last instar larvae of three species, only in few individuals selected tergalius I (either left or right one), was not folded, but spread as in younger larvae.

Other tergalii II–VII have no overturned anal lobe; their anal margin either has no anal rib, or has very short anal rib, that varies individually and among tergalii of one individual (Kluge et al. 2017: Fig.25-29, 86-91). Costal margin is armed by costal rib, which in its distal part bears small seta-bearing denticles.

Superficially, last instar larval tergalii of Crassabwa/g2 resemble that of Susua, Dabulamanzia and Cheleocloeon, whose tergalii I are petiolate and sharply different from others; in contrast to these taxa, in Crassabwa/g2 tergalii I are not really petiolate, but get this shape due to folding. Among Baetidae, besides Crassabwa/g2, tergalii with overturned anal lobe are found only in Cloeon/fg1 and Callibaetis/fg2; in contrast to Crassabwa/g1, anal lobe of Cloeon/fg1 is bent not ventrally, but dorsally and can be present on tergalii of several pairs; in Callibaetis/fg2 the anal lobe bent ventrally is present on tergalii of several or all pairs.

(2) Pigmentation of tergalii. Dorsal cuticle of each tergalius I–VII can have a brown stripe running just above main trachea; in flavum [Centroptilum] this stripe is wider than trachea (Kluge et al. 2017: Fig.29–30); in ludmilae [Crassabwa] this stripe is not wider than trachea, so that is invisible on background of trachea (Kluge et al. 2017: Fig.92–93); in some individuals of ludmilae [Crassabwa] and ameliae [Crassabwa] this stripe is completely absent.

(3) Larval abdominal tergum X. Anterior margin of abdominal tergum X forms a pair of prominent projections (Kluge et al. 2017: Fig.65), which serve as places of attachment for various longitudinal dorsal muscles running from anterior margin of tergum IX and from previous abdominal terga. In other taxa, including Susua, anterior margin of this tergum is either nearly straight, or forms a pair of shallow convexities.

(4) Chape of wings. Hind wing present in both sexes, of «Centroptilum-type»: narrow, with fore margin nearly straight and hind margin slightly convex, with 2 longitudinal veins, with hooked costal projection; in contrast to other taxa with the «Centroptilum-type» hind wing, in  Crassabwa/g2 costal projection is especially long and directed perpendicular to the wing; fore wing is widest near base, gradually narrowing toward apex (the same in various relatively large Turbanoculata, in contrast to smaller Turbanoculata, whose wings are more oval and widest near middle). (Kluge et al. 2017: Fig.51-55). The same in the species of unclear systematic position vitreum [Cloeon].

(5) Shape of styliger. At least in flavum [Centroptilum] and ludmilae [Crassabwa] apical margin of each unistyliger bears a median projection, which represents continuation of dorsal wall of unistyliger and is projected in medio-ventral direction (Kluge et al. 2017: Fig.37-39, 41, 106).

Characters of Crassabwa/g2 of unclear phylogenetic status. 

(6) Postsubalar sclerite. Postsubalare has posterior-dorsal corner stretched to a thin process with concave dorsal margin (Kluge et al. 2017: Fig.36, 98) (this is similar to Cloeon/fg1, but differs from Susua and many other taxa, whose posterior-dorsal process is wider, with convex dorsal margin – Kluge et al. 2018: Fig.49, 102).

(7) Denticles on larval abdomen. Posterior margins of abdominal terga II–X with regular row of large, narrow, pointed denticles, which can alternate with smaller denticles (Kluge et al. 2017: Fig.20); posterior margin of each caudalius segment bears denticles, which are enlarged on lateral sides of cerci and on dorsal side of paracercus, being somewhat larger on each 2nd segment (Kluge et al. 2017: Fig.63) (in contrast to Susua, whose denticles are much smaller).

Plesiomorphy of Crassabwa/g2.

(8) Mobility of tergalii. In contrast to Sususa, tergalii af all pairsretain ability to make rhythmical respiratory movements with little amplitude. However, in contrast to other mayflies able to such movements, larvae of Crassabwa/g2 are unable to live in stagnant water, so it is rather difficult to transport living larvae from place of collecting to a cage placed on current, and impossible to keep them in container for rearing. Crass (1947) also noted that «The nymphs have proved very intolerant of captivity».