CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Callibaetis/fg1.

(1) Labrum and hypopharynx form a peculiar grasping apparatus: Labrum has a pair of sclerotized protuberances on sides of its median incision [see Turbanoculata (4)]; apex of hypopharynx has an unpaired sclerotized protuberance on dorsal side; when labrum and hypopharynx are pressed together, the sclerotized protuberance of hypopharynx is inserted between the sclerotized protuberances of labrum. Usually the protuberances of labrum are distinctly outlined, but in floridanus [Callibaetis] they are fused with other sclerotization of distal margin of labrum.

(2) Mandibles are characteristic and uniform in all representatives: outer margin laterad of incisor convex, denticles of «Centroptilum-type»: kinetodontium is separated from incisor (but immovable) and rotated perpendicular to plane of mandible, so that its denticles hide one another in dorsal or ventral view; left prostheca is bifurcate and rotated in the same manner (Fig. ) (see Index of characters [1.1.22], [1.1.24]); right prostheca bifurcate.

(3) Maxilla always has characteristic shape: relatively short, with especially convex outer margin.

(4) Labial palp has boundary between 2^nd and 3^rd segments oblique, so that 2^nd segment is long at outer side and short at inner side; 2^nd and 3^rd segments together form integral figure. 

Characters of Callibaetis/fg1 of unclear phylogenetic status. 

(5) Unlike other Turbanoculata, in Callibaetis/fg1 external larval gonostyli buds are long, projected far behind sternum IX; this resembles a plesiomorphic condition present in Siphlaenigma and majority of other Ephemeroptera. In mature larva ready to moult to subimago, buds of subimaginal gonostyli are folded under larval cuticle ?similar to the "Nigrobaetis-type":??? 2^nd segment of gonostylus is directed posteriorly and curved by its convexity medially and by apex laterally [see Baetovectata (3)] (see Index of characters [2.3.9]).

(6) Larval antennae bases are not brought together, frons between them does not form a keel (unlike Paracloeodes and some Baetungulata – see Index of characters [1.1.3]).

(7) Tergalii are able to make rhythmical respiratory movements (see Index of characters [1.3.30]).

Plesiomorphies of Callibaetis/fg1.

Hind wings are always developed [being strongly diminished – see Turbanoculata (10)]. 

Larva always of siphlonuroid (actively-swimming) type: legs slender, not tenacious; abdomen large, not flattened ventrally (terga not wider than sterna), paracercus and primary swimming setae well-developed. Larval claw with 2 rows of denticles [see Tetramerotarsata (11); see bellow, Callibaetis/fg2 (3)].

Variable characters of Callibaetis/fg1. On fore wing intercalaries are situated mainly in twos in each field [see Baetovectata (1)]; sometimes one of two veins is lost, and in each field a single intercalary is present, being situated either eccentrically, or in centre of field; sometimes male has two intercalaries, and female has one intercalary in each space.