CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Securiops.

(1) Larva is psammophylous, with adaptation for inhabitancy on sandy ground: legs are long and slender, with long claws (Kluge 2023: Figs 28, 67, 112–114); mouth apparatus is modified, with labium greatly elongated; labium, maxillae and labrum having peculiar shape and setation:

Labrum (Kluge 2023: Figs 31–33, 100). Distal margin is nearly straight (neither sharply concave, nor sharply convex); median incision is wide and shallow; other distal margin is distinctly differentiated into paired submedian and paired lateral portions. The submedian portion has a groove bordered by a more prominent ventral flange and a less prominent dorsal flange; the regular row of marginal setae is attached inside this groove, between these two flanges. The lateral portion has no groove, and the regular row of marginal setae is attached openly on its distal margin. This structure of distal margin is different both from sharply concave in Pseudocentroptiloides/g1, and from convex or straight with narrow median incision in other Procloeon/g1 and most other Baetidae (Kluge 2016: Fig. 43; Kluge 2020: Fig. 16; Kluge 2020: Figs 49–50).

Maxillae (Kluge 2023: Figs 36–38). The 2nd and the 3rd dentisetae are located at a distance from the 1st dentiseta, nearer to the proximal angle of biting margin; a few small setae are located between the 1st and the 2nd dentiseta. In other respects maxilla retains plesiomorphic structure: apex is pointed, with 3 long, slender, arched maxillary canines; the 1st dentiseta has the same shape as the canines and is pressed to the canines. In other Procloeon/g1, the 2nd and the 3rd dentisetae are located close to the 1st dentiseta (e.g., Kluge 2016: Fig. 46; Kluge 2020: Fig. 17; Kluge 2020: Fig. 53).

Labium (Kluge 2023: Figs 40–46, 116–119). Paraglossae are greatly enlarged, three times longer than glossae; glossae and paraglossae are highly modified, with shape and setation different from the initial one (see below); labial palp is greatly widened apically (see below).

Glossa is short, with apex rounded. Ventral side of glossa proximally with a regular transverse row of very long and straight setae; being pressed on slide, these setae can be turned either proximally (Kluge 2023: Fig. 43), or distally (Kluge 2023: Fig. 41, 42, 45). Dorsal side of glossa distally with a regular, arched, transverse row of stout, pointed setae directed distally (Kluge 2023: Fig. 46). Rounded apex of glossa is smooth, without setae. Glossa of Securiops differs from the initial one (Kluge 2016: 137–138 and Figs 4–5; Kluge 2016: Figs 47–48), in that its apex is not pointed and lacks setae, but the marginal setal row is shifted to the dorsal side. Origin of the peculiar transverse ventral-proximal row of straight setae is unclear.

Paraglossae are very large and flattened, either oval (Kluge 2023: Figs 40–43), or with inner margins angulate and diverging (Kluge 2023: Fig. 116). Most surface of ventral and dorsal sides is smooth, lacking setae; lateral margin with a regular longitudinal row of long setae; median side with two regular longitudinal rows of larger setae and one longitudinal row of smaller setae dorsad of them. Paraglossa of Securiops differs from the initial one (Kluge 2016: 137–138 and Figs 4–5; Kluge 2016: Figs 47–48), in that its apex is not pointed, and median margin is not evenly concave; possibly, two of the three regular setal rows along the median margin are homologous to the ventro-median and the dorso-median setal rows of the initial structure, and the setae on lateral margin correspond to the latero-apical setae of the initial structure.

Labial palp (with 3rd segment initially truncate) has 3rd+2nd segments greatly widened, triangular, with straight distal margin of the 3rd segment exceeding median margin of the 3rd+2nd segments; angle formed by lateral and distal margins is bent and stretched forming a small projection (Kluge 2023: Fig. 44, 116–117). Border between 2nd and the 3rd segments is retained, as well as the muscle going from the 2nd segment to the base of 3rd segment (Kluge 2023: Figs 40, 44).

Characters of Securiops of unclear phylogenetic status. 

(2) Mandibles (Kluge 2023: Figs 34–35, 98–99) of the «Centroptilum-type»: the kinetodontium is deeply separated from the incisor and rotated perpendicular to the plane of the mandible, so that its denticles hide one another in dorsal or ventral view; the left prostheca is bifurcate and rotated in the same manner. Among Procloeon/g1, such «Centroptilum-type» of mandibles, besides Securiops occurs in Pseudocentroptiloides/g1 and Monilistylus as well; it is also present in some other baetid taxa (Kluge 2020: Figs 18–23; Kluge 2020: 440 and Figs 13–15).

(3) Larval femur without two subapical setae (in contrast to Oculogaster and various taxa not belonging to Cloeon/fg1); apical margin of femur lacks stout setae (Kluge 2023: Fig. 47).

(4) Larval claws are long, slender and slightly arched, without denticles and without oblique striation; only faint longitudinal striation is present on narrow distal part (Kluge 2023: Fig. 50). The same in some other Procloeon/g1 and in some other Baetidae.

Variable characters of Securiops. Hind wings [of the «Centroptilum-type» – see Cloeon/fg1 (9)] are either present (in  falcatum [Centroptilum], macafertiorum [Potamocloeon]) or absent (see Index of characters [2.2.59]).