(Panephemeroptera Euephemeroptera Euplectoptera Anteritorna pm.Tridentiseta
 - Ameletus/fg1)

Nomen hierarchicum: Ameletus/fg1 [f:1991; g:1885] (incl. Metreletus 

In circumscription fits:

— gen. Ameletus: Fizaine 1931: 25

— Ameletus-complex: Koss & Edmunds 1974: 301

— fam. Ameletidae: Kluge & Studemann & Landolt & Gonser 1995: 111

— Ameletus/fg1: Kluge 2004: 80

References. Koss & Edmunds 1974: *; – Kluge & al. 1995: * * * *; – Kluge 2004: * * *; – Kluge 2007: * * *.

Autapomorphies of Ameletus/fg1.

(1) Mouth apparatus is specialized, with mouthparts elongate and maxillae filtering (Eaton 1883-1888: Pl.49:4-9). Labrum is more or less elongate. Mandibles are elongate perpendicular to their axis of articulation, with thin weak incisor and kinetodontium, prostheca on left mandible is setiform, on right mandible is lost. Maxilla is strongly modified: its apical margin is widened, pectinate setae of apical-ventral row are elongate, forming a filtering apparatus; maxillary canines are completely lost, among dentisetae only one is retained, being poorly visible and directed dorsally (Kluge 2004: Fig.20:B-C). Unlike other parts, labium is not elongate (Kluge 2004: Fig.20:A, D).

(2) Imaginal and subimaginal lateroparapsidal suture is elongate; subimaginal lateral pigmented area of mesonotum includes entire sublateroscutum and submedioscutum up to medioparapsidal suture (Kluge 2004: Fig.21:B). Similar form of this area in Isonychia/fg1 only (see Index of characters [2.2.14]).

(3) Imaginal and subimaginal epimeron of mesothorax has a membranous area between anepimeron and katepimeron (Kluge 2004: Fig.21:C).

(4) Tergalii (see Variable characters) lost ability of rhythmical respiratory movements. Non-unique apomorphy (see Index of characters [1.3.30]). Larvae inhabit mountain streams and lakes with high oxygen concentration, thus usually do not need in respiratory movements. Being placed into stagnant water with low oxygen concentration, larva does not move by its tergalii, but makes dorsoventral undulation by abdomen (Kluge 2004: Fig.9:I-M). Such respiratory movement is rather primitive, as it proceeds from the initial swimming movement (see Plesiomorphies), but is done slower and with legs fixed on the substrate (Kluge & Novikova & Brodsky 1984).

(5) Male imaginal styliger dorsally has a membranous area (Kluge 2004: Fig.11:B-D).

(6) Imaginal penis bears a pair of sclerotized lateral lobes located laterad-distad of gonopores, and a pair of membranous or sclerotized ventral plates located proximad of gonopores (Kluge 2004: Fig.11:B-D, Kluge 2007: Fig.11-12).

(7) Imaginal and subimaginal paracercus is vestigial (Kluge 2004: Fig.11:B-C). Non-unique apomorphy (see Index of characters [2.3.22]); particularly, the same in Siphlonurus/fg1 and Metretopus/fg1.

Plesiomorphies of Ameletus/fg1. Larva has primary swimming siphlonuroid specialization: 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 [see (1)], 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.

In imago and subimago: Mesonotal suture is stretched backward medially (Kluge 2004: Fig.21:B-C). Anterior paracoxal suture is complete (Kluge 2004: Fig.21:C) (unlike Rallidens and some Bidentiseta). Furcasternal protuberances are contiguous (unlike Amphinotic groups of Tridentiseta and some others – see Index of characters [2.2.23]). Hind wing is well-developed, as long as 0.35–0.4 of fore wing length. Imaginal and subimaginal tarsi are 5-segmented, 1st segment is non-shortened and fused with tibia. All claws of imago and subimago are ephemeropteroid. Gonostylus has 2 distal segments.

Variable characters of Ameletus/fg1. In different species costal and anal ribs are either present on all tergalii I–VII, or lost on tergalii I–II; anal rib can be located either far from anal margin or close to anal margin; tergalius margin usually with denticles at apical part of costal rib and at the place where anal rib reaches anal margin (Zloty 1997: Fig.22-23).

Size. Fore wing length 7–17 mm.

Age and distribution. Palaeogene – recent; Holarctic and Oriental Region. A reliably determined fossil specimen is a female imago from Baltic amber (deposited in Mus. Nat. Hist. of Inst. Syst. Evol. Anim. in Krakow), which has characteristic epimeron structure [see (3)]; its wing venation has plesiomorphic condition characteristic for Ameletus/fg2.

The taxon Ameletus/fg1 is divided into:

1. Metreletus

2. extinct Electroletus

3. Ameletus/fg2