CLADOENDESIS OF EPHEMEROPTERA

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Characters of Euephemeroptera of unclear phylogenetic status.

(1) Wings of both pairs have a costal brace – a short vein, which goes from wing base between C and Sc, falls into Sc and at the same place is connected by a cross vein with RA. Unique character. For Protephemeroidea costal brace is not described. In known Permoplectoptera costal brace is situated between C and Sc (Kluge 2004: Fig.14:B), but in Euplectoptera it is stout, convex anteriorly, and projects dorsad-anteriad of C (Kluge 2004: Fig.6); only in Discoglossata it is modified (Kluge 2004: Fig.42:A).

(2) Vein RS arises not from RA, but from MA (unlike Protephemeroidea); the common basal stem RS+MA can be independent from RA (Kluge 2004: Fig.7:C), or basally fused with RA (particularly on hind wings of Euplectoptera – Fig.7:D), or secondary reduced (Kluge 2004: Fig.17:A). Non-unique character, the same in some other Pterygota.

(3) Vein RSa₂ [concave – see Panephemeroptera (4)] forms a triad of concave RSa₂' and RSa₂'' and convex iRSa₂ between them (Kluge 2004: Fig.7:C). Unique character. This third triad of RS is present on wings of both pairs in Permoplectoptera and fore wings of many Euplectoptera [but not on their hind wings – see Euplectoptera (1) below]; on fore wings of some Euplectoptera veins RSa₂' and iRSa₂ secondarily become intercalaries or lost (see Index of characters [2.2.38–39]).

(4) On wings of both pairs MA [convex – see Panephemeroptera (3)] forms a triad of convex MA₁ and MA₂ and concave iMA between them (Kluge 2004: Fig.7:C-D). This branching of MA secondary disappears on vestigial hind winds of some Euplectoptera and on fore wings in some groups with especially modified venation (see Index of characters [2.2.43]). Usually furcation of MA is situated approximately in middle of wing, but sometimes it can be secondarily transferred proximally (on fore wings of some specialized Euplectoptera) or toward wing margin (on vestigial hind wings of some Euplectoptera).

(5) Larva is aquatic, with peculiar specialization for swimming (called siphlonuroid specialization) (Kluge 2004: Fig.9:A-B, 14:C-D, 28:A): abdomen is elongate and able to make undulate dorsoventral swimming movements; caudalii are not long (shorter than in imago), with primary swimming setae - i.e. each cercus has a row of setae on inner side, and paracercus has a pair of rows of setae of the same kind on its lateral sides; thanks to this, caudalii can function as a horizontal caudal flipper. As larvae of other Panephemeroptera are unknown, it is unclear if this specialization is an autapomorphy of Euephemeroptera or an autapomorphy of a larger taxon. In many Euplectoptera this swimming specialization is secondarily lost.

(6) Larva has tergalii on abdominal segments I–IX (Kluge 2004: Fig.14:D). As larvae of other Panephemeroptera are unknown for certain, it is unclear, if the presence of tergalii is a character of Euephemeroptera or of a larger taxon; if proceed from the assumption that tergalii are serial homologues of wings, their presence is a plesiomorphy. In various Euephemeroptera tergalii of these or that pairs are lost (see Index of characters [1.3.20–21]).