Eusetisura, or Oligoneuria/f1=g2

(Panephemeroptera Euephemeroptera Euplectoptera Anteritorna Bidentiseta Branchitergaliae - Eusetisura)

Nomen hierarchicum: Oligoneuria/f1=g2 [f:1914; g:1843] (incl. Coloburiscus, Isonychia  

Nomen circumscribens: Eusetisura Kluge 1998: 256. 

In circumscription fits:

 subtribus Oligoneuriina: Lameere 1917: 62

 fam. Oligoneuriidae: Riek 1973: 164

 superfam. Oligoneurioidea: Kluge & Studemann & Landolt & Gonser 1995: 105

 Eusetisura Kluge 1998: 256

 Eusetisura = Oligoneuria/f1=g2: Kluge 2000: 251

References. Lameere 1917: * *; Riek 1973: *; McCafferty & Edmunds 1979: *; Kluge 2004: * * * *. 

Autapomorphies of Eusetisura.

(1) Larval fore legs are specialized as filtering, with femur and tibia modified (Kluge 2004: Fig.38:B, 41:E, 44:A; Kluge 2007: Fig.1): On inner side of femur long filtering setae form 2 longitudinal rows, which convergent proximally. Inner side of fore tibia (lacking patella-tibial suture, as in most mayflies) is convex in its proximal part, thus tibia in this part is thickened or curved, unlike tibiae of middle and hind legs; on inner side of tibia long filtering setae also form 2 regular longitudinal rows convergenting proximally (Kluge 2004: Fig.38:B). Filtering setae of femur and tibia have such structure of their bases, which allow them to fold along the leg; these setae can bear thin seta-like processes, especially prominent in Discoglossata. 

Similar setal rows on inner side of fore femur and tibia, besides Eusetisura, are present in Polymitarcys/f1=Ephoron/g2 only (Kluge 2004: Fig.77:C); in other mayflies, if fore tibia has two regular rows of filtering setae (for example, in Hagenulus/fg*), the form of fore tibia does not differ from middle and hind ones, and femur has no two rows of setae.

(2) Maxillary and labial palps are specialized for gathering food particles dispersed in water: each palp has 2nd+3rd segment massive, densely covered with long thin setae (non-unique apomorphy see Index of characters [1.1.44] and [1.1.57]). Degree of fusion of 2nd and 3rd segments varies: boundary between them is retained in Coloburiscus/fg1 (Kluge 2004: Fig.37:D), but lost in Isonychia/fg1 (Kluge 2004: Fig.41:B) and Discoglossata (Kluge 2004: Fig.45:B), muscle inside 2nd segment of labial palp is retained in Coloburiscoides (Kluge 2004: Fig.37:D), Coloburiscus/fg3 and Isonychia/fg1 (Kluge 2004: Fig.41:B), but lost in Murphyella and Discoglossata.

(3) Base of each maxilla [see (4)] bears a tracheal gill in a form of soft process or a tuft of processes; this gill arises from articulatory membrane, which connects posterior (or ventral) side of stipes and cardo with ventral side of head (Kluge 2004: Fig.37:C, 41:D; Eaton 1883-1888: Pl.26:11). Unique apomorphy; in other mayflies similar gills evolved independently on variable parts of  body, including maxillae, but not exactly on the same place as in Eusetisura (for example, in Nesameletus/f1=Metamonius/g1 and Rallidens a gill is present on lateral side of maxilla, in articulation of cardo with stipes. Besides the gills on maxillae, which are present in all Eusetisura, other gills can be present: on sides of mentum between paraglossae and bases of labial palps (in Murphyella and Coloburiscoides Kluge 2004: Fig.37:D); on median side of joining of fore coxae with sternum (in Murphyella and Isonychia/fg1 Kluge 2004: Fig.41:E); at the middle of prosternum, mesosternum and metasternum (in Murphyella only). 

(4) Maxilla lacks regular apical-ventral row of setae (non-unique character see Index of characters [1.1.31]); apical and lateral sides bear more or less dense long simple irregular setae (Kluge 2004: Fig.37:C).

(5) Larval fore protoptera are fused with scutellum up to apex of scutellum. Non-unique apomorphy (see Index of characters [1.2.6]); in Isonychia/fg1 fore protoptera are separated beginning from the apex of scutellum (Kluge 2004: Fig.40:C), while in other taxa they are variously fused one with another behind scutellum (Kluge 2004: Fig.37:A, 44:A) [see below, Coloburiscus/fg1 (2) and Discoglossata (3)]. Mesal plate between fore protoptera can contain plumidia anlages: in Isonychia/fg1 such anlages occur at the beginning of last larval instar (Kluge 2004: Fig.40:C), but disappear at the end of this instar, and their space is filled by crumpled subimaginal wings; in Geminovenata plumidia anlages (Kluge 2004: Fig.44:A) develop to adult plumidia a pair of membranous processes on posterior margin of scutellum (Kluge 2004: Fig.46:A,C; Kluge 2007: Fig.13). Non-unique apomorphy (see Index of characters [1.2.6] and [2.2.13]).

Characters of Eusetisura of unclear phylogenetic status. 

(6) Larval claws usually with one row of denticles on inner margin (only in Coloburiscus/fg2 and Homoeoneuria/g2 denticles are absent, and in Oligoneurisca denticles form two rows). Non-unique character (see Index of characters [1.2.21]).

(7) Tergalii lost ability to make rhythmical respiratory movements (at least in the species examined). Non-unique apomorphy (see Index of characters [1.3.30]). Well-developed lamellate lobes of tergalii [bearing fibrillose branchial lobes see Branchitergaliae (3)] are present in Isonychia/fg1 and some Geminovenata, while in Coloburiscus/fg1, Chromarcys and many Geminovenata the lamellate lobes are diminished, sclerotized and useless for respiration.

Plesiomorphies of Eusetisura. Larval caudalii nearly always retain well-developed primary swimming setae (these setae are lost in Coloburiscus/fg2 only) and never have secondary swimming setae.

In imago and subimago: Anterior paracoxal suture is complete (unlike Heptagennota and some others); furcasternal protuberances are contiguous (Kluge 2004: Fig.39:A-B, 40:E-F, 46:C-D) (only in females of Geminovenata they are separated at posterior part). 1st tarsal segment is fused with tibia (unlike Pentamerotarsata).

Size. Fore wing length 727 mm. 

Age and distribution.  Possibly, Late Jurassic (see Eusetisura INCERTAE SEDIS) Recent; world-wide.

The taxon Eusetisura (or Oligoneuria/f1=g2) ise divided into:

1. Coloburiscus/fg1

1.1. Coloburiscoides

1.2. Coloburiscus/fg2

1.2.1. plesiomorphon Coloburiscus/fg3

1.2.2. Murphyella

2. Isonychia/fg1

2.1. Isonychia/fg2

2.2. Prionoides

3. Discoglossata (or Oligoneuria/f2=g3)

3.1. Chromarcys

3.2. Geminovenata, or Oligoneuria/f3=g4

Some extinct Mesozoic taxa have uncertain systematic position