CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphies of Siphlonurus/fg1.

(1) In female imago distal portion of seminal receptacle is sclerotized and transformed to a peculiar copulatory pouch situated in abdominal segment VIII (Kluge 2004: Fig.18:A-C, 19:A-B,G). Posteriorly from copulatory pouch arises a membranous duct, which opens to copulatory opening (situated at boundary of abdominal sterna VIII and IX); from postero-lateral portions of the copulatory pouch arise a pair of oviducts, and anteriorly from copulatory pouch arises a membranous seminal receptacle. Structure of copulatory pouch is species-specific. (As copulatory pouch is covered by muscles, it is invisible neither when abdomen is dissected, nor on translucent slide in Canadian balsam; it can be studied if treat abdomen by alkali to dissolve all tissues and retain cuticle only.) In female subimago sclerotized copulatory pouch is absent. Unique apomorphy: in all other mayflies (including Dipteromimus, Ameletus/fg1, Metretopus/fg1, Acanthametropus/fg1, Ametropus, Nesameletus/f1=Metamonius/g1, Vetulata, Ameletopsis/fg1 and Rallidens, which were formerly mixed with Siphlonurus/fg1) the whole female copulatory apparatus is membranous.

(2) Egg surface has convex rough buttons formed by tops of threads closely pressed together (Kluge & al. 1995: Fig.61-63) (for detailed description of these structures see Gaino & Debora 2001). In other mayflies, if anchors in a form of bundle of threads are present, end of each bundle is covered by integral knob or by a regular rosette-like structure (in Ameletus/fg1, Metretopus/fg1 and some others). Probably, opened tops of bundles in Siphlonurus/fg1 were formed as a result of reduction of the knobs.

(3) Each paired penis lobe is distally split into two lobes – gonopore-bearing medial (or ventral) one and additional lateral (or dorsal) one; shape of these lobes is species-specific.

Characters of Siphlonurus/fg1 of unclear phylogenetic status.

(4) Imaginal and subimaginal claws (initially ephemeropteroid) on each leg are similar and pointed (Kluge 2004: Fig.4:A-B). Non-unique apomorphy (see Index of characters [2.2.85]); among Tridentiseta the same in Dipteromimus and Nesameletus/f1=Metamonius/g1.

(5) Imaginal and subimaginal paracercus is vestigial. Non-unique apomorphy (see Index of characters [2.3.22]); particularly, the same in Ameletus/fg1 and Metretopus/fg1.

(6) Larval abdominal terga and sterna with more or less developed spine-like setae (non-unique character; the same in Metretopus/fg1-Siphloplecton, some Ameletus/fg2 and others). Posterior margins of sterna always lack denticles, posterior margins of terga either with denticles (in Siphlonurus/fg2) or not (in Parameletus/fg1).

(7) On each tergalius I–VII anal rib is located very far from anal margin, on dorsal surface, at anterior half of tergalius, usually just behind middle trachea (while costal rib has usual for mayflies position on costal margin and is developed at least in proximal part of tergalius) (Kluge 2004: Fig.18:F). The same in Dipteromimus and some others (see Index of characters [1.3.28]).

Plesiomorphies of Siphlonurus/fg1. Larva has primary swimming siphlonuroid specialization (Eaton 1883–1888: Pl.50: 1–3): legs are able to stretch posteriorly; abdomen is large, able to make undulate swimming movements; caudalii are not long, paracercus is well-developed, primary swimming setae are dense, secondary swimming setae are absent. Larval head is hypognathous, mouth apparatus is non-specialized (Kluge 2004: Fig.3:A); maxilla has 3 canines and 3 dentisetae [see Anteritorna (2)] (Kluge 2004: Fig.3:B,E), setae of apical-ventral row can be from simple to pectinate (only in Siphlonisca absent); maxillary palp is 3-segmented; labial palp is 3-segmented. Larval (and adult) patella-tibial suture is developed on middle and hind legs only. Larval claws are slightly curved, without denticles or with very small irregular denticles near base. Tergalii [see (7)] retain ability of rhythmical respiratory movement (see Index of characters [1.3.30]).

In imago and subimago: Mesonotal suture can be stretched backward medially (especially in Siphlonurus/fg3) or nearly transverse (especially in Parameletus/fg2). Anterior paracoxal suture is complete (Kluge 2004: Fig.5:A,  5:C) (unlike Rallidens and some Bidentiseta). Furcasternal protuberances are contiguous (Kluge 2004: Fig.5:C) (unlike Amphinotic groups of Tridentiseta and some others – see Index of characters [2.2.23]). Subimaginal lateral sclerotized pigmented area of mesonotum is small, bifurcates posteriorly in such a manner, that one its branch stretches along lateroparapsidal suture, and another branch – along lateral scutal suture (Kluge 2004: Fig.18:E) (see Index of characters [2.2.14]). In cubital field of fore wing several (3–9) veins go from CuA to basitornal margin [see Anteritorna (1)]; hind wing is well-developed, as long as 0.4–0.5 of fore wing length (Kluge 2004: Fig.7:C-D). Imaginal and subimaginal tarsi are 5-segmented, 1^st segment is the longest, fused with tibia (Kluge 2004: Fig.4). Gonostylus has 2 distal segments.