Asthenopus Eaton

Molineri, Carlos, Salles, Frederico F. & Peters, Janice G., 2015, Phylogeny and biogeography of Asthenopodinae with a revision of Asthenopus, reinstatement of Asthenopodes, and the description of the new genera Hubbardipes and Priasthenopus (Ephemeroptera, Polymitarcyidae), ZooKeys 478, pp. 45-128 : 80-82

Taxon classification Animalia Ephemeroptera Polymitarcyidae

Asthenopus Eaton Figs 4 C–D, 14, 15, 16, 17, 18, 20 F–J

Asthenopus Eaton 1871: 59; Lestage 1922: 142; Traver 1950: 605; Traver 1956 b: 7; Hubbard and Domínguez 1988: 209; Domínguez 1988 a: 24.

Type-species.

Palingenia curta Hagen, original designation.

Species included.

Asthenopus curtus , Asthenopus angelae , Asthenopus magnus sp. n., Asthenopus hubbardi sp. n., Asthenopus guarani sp. n.

Diagnosis.

Five autapomorphies were recovered for Asthenopus : 1) character 1 (ratio length second foretarsal segment/foretibia) decreases from 0.645-0.652 to 0.584-0.587; 2) char. 7 (marginal connectivity = n°of connections among imv/n°of imv) decreases from 0.700-1.167 to 0.222-0.300; 3) male foretarsal segment 1 subrectangular; 4) penes with an apical spine; and 5) long and open cleft present between penial lobe and thumb. The following combination of characters is useful to distinguish Asthenopus from other genera in Polymitarcyidae : 1) ratio length male FW/foreleg = 1.4-1.8; 2) tarsal segment 1 distinct and subrectangular in form (not fused to tibia), ratio subapical width of foretibia/subbasal width of second tarsal segment 1.5-2.3 (Fig. 20 F–J); 3) pronotum width/length ratio 1.7-2.4 (male, but frequently around 2.0), 2.0-3.0 (female); 4) in both sexes FW marginal intercalary veins short and not anastomosed (4-25 in number, Fig. 16); 5) in both sexes FW with 0-4 (most commonly 2, but variable depending on size of specimen) crossveins between R and M, basally to R fork; 6) FW vein IMP basally free, subequal in length to MP2, forming a characteristic oblique “Y” with associated cross veins (arrow Fig. 16A, E); 7) median remnant of styliger plate present, pedestals well developed (Fig. 17); 8) forceps relatively stout, ratio length/basal-width = 4.7-7.0; 9) penes relatively short and stout, curved ventrally (and medially), with a thumb attached at the base, and with the apex of penial lobe distinctly shaped as a spine; 10) female abdominal sternum VIII with anteromedian paired sockets, much reduced in size, and with a keel as in Figs 18 F–H; 11) eggs with relatively large polar caps formed by 3-8 (commonly 5) long coiled threads, chorion covered with disk-like structures (Fig. 18 A–E); 12) head dorsally strongly convex on occiput, frons not projecting medially (Fig. 14 I–J); 13) nymphs with very short and robust tusks (Fig. 14 A–C, E–G), with large submedian inner tubercle, with 2 or 3-pointed apex (asymmetric); 14) nymphal foretarsal claw with a single row of denticles (Fig. 15G); 15) apex of femur 3 with a group of ca. 50 stout pointed spines (Fig. 15F).

Male imago. Length: body, 6.5-10.5; FW, 7.0-10.1; HW, 2.9-4.8; foreleg, 5.1-7.5; cerci, 22.0-37.0. Antennae: scape slightly longer than pedicel, flagellum bristle-like. Thorax. Pronotum width/length: 1.7-2.4. Legs. Forelegs subequal to shorter than body, ratio length FW/foreleg 1.4-1.8; longest segment is tibia (ratio length tarsal segment 2/tibia = 0.4-0.7); tarsal segment 1 distinct, not fused, very short (Fig. 20 F–J); remaining tarsal segments relatively short subequal in length except tarsal segment 2 slightly longer; claws differing in length, one long the other short, very slightly widened distally. Wings (Fig. 16). FW with 4-25 marginal intercalaries, sometimes present in HW but not in all spaces; intercalaries not strongly anastomosed; 0-4 cross veins between MA and R, basad to R stem; R stem length/Rs from fork to margin = 0.17-0.31. Ratio MA length from fork to margin/stem length = 7-15; IMP fused basally to MP1 or free; MP2 fused to IMP. Genitalia (Fig. 17): median remnant of styliger plate subrectangular to subovate; pedestals subrectangular to subovate, relatively small; forceps relatively wide to very wide, ratio length/basal width 4.7-7.0; penes tubular and robust, curved ventro-medially, and with well-developed basal thumb. Terminal filament reduced, cerci long (ratio length FW/cercus = 0.25-0.36).

Female adult. Length: body, 8.0-19.5; FW, 12.0-18.5; HW, 4.6-7.8; cerci, 3.0-7.0. Thorax. Pronotum width/length = 2-3. Wings with more crossveins and intercalaries than in male. Abdominal sternum VIII with anteromedian keel (Fig. 18 F–H), at each side of keel´s base a very small “socket” is present ( “s” in Fig. 18F). Terminal filament reduced, shorter than tergum VIII, with few thin annuli. Cercus short, 0.25-0.50 times length of FW.

Eggs (Fig. 18 A–E). Length, 210-285 µ; width, 135-163 µ. Oval (ratio maximum length / maximum width = 1.4-1.8), with two relatively large polar caps (ratio maximum with of egg/maximum width of uncoiled polar cap = 1.1-1.5), formed by 3-8 very long coiled threads. Chorionic surface with large subcircular chorionic plates, sometimes each plate is divided in 2-3 portions.

Nymphs. Length (mm): body, 9.7-15.0 mm; cerci, 4.0-7.0; terminal filament, 5.0-5.1. Head suboval in dorsal view, smooth (without pilose area); occipital region well developed, strongly convex (Figs 4 C–D, 14 I–J). Head capsule with a dorsal spine-like projection at bases of antennae. Antennae 1.1-1.5 times length of head (length of head taken from hind margin to the apex of clypeus); pedicel with tuft of setae on dorsum, flagellum with minute scattered setae; length (mm): scape (0.5), pedicel (0.28), flagellum (2.0). Frons with anterior margin more or less straight (arrow in Fig. 14J), with a small blunt lateral projection ( “a” in Fig. 14I), without median projection. Clypeus and labrum small, membranous, with many setae on dorsum of labrum. Mandibular tusks robust, relatively stout, left tusk (Fig. 14 A–C, E) with 3 apical teeth, increasing in size from the median (smallest), inner and outer; inner tooth slightly directed medially, others directed distally; right tusk (Fig. 14 F–G) with 2 teeth, the inner shorter. Inner margin of both tusks with a rounded small tubercle near subapex and a larger and pointed subbasal tubercle (associated with a tuft of rigid setae), this large basal tubercle shows a small basal protuberance (giving the impression of a bifid tubercle but with one of the sides aborted); ventral surface and outer margin of tusks with small rounded protuberances on the extremely hard cuticle; dorsal surface of tusks with numerous setae and with a small basal tubercle; this small dorsal tubercle is easily seen without dissecting the mandible and gives an additional point of articulation between the mandible and the head capsule ( “a” and “b” in Fig. 14I). Incisors and prostheca of both mandibles very reduced in size, molae relatively well developed. Maxillae with a small subtriangular basal membranous “gill” (membranous outgrouth). Thorax. Anterior ring of pronotum (or collar sensu Kluge 2004) short (ca. 1/4 the length of posterior ring), anteriorly projecting as spines on lateral corners; posterior ring longer, ring-like. Legs (Fig. 15 A–D, F–G). Leg I (Fig. 15 A–B): femora very wide, well developed, with a double ventro-basal row of long filtering setae; tibio-tarsus (fused, but fusion line distinguishable) with 3 rows of filtering setae (2 on dorsal “face” and 1 on inner margin), tarsus slightly and bluntly projecting apically (arrow in Fig. 15B); tarsal claw relatively large and stout with a row of marginal denticles (Fig. 15G). Leg II (Fig. 15C): smaller, with thinner femora, with scattered long setae, mostly basally and along hind margin; tibia and tarsi with row of long setae on outer (dorsal) margin, ventrally with many stout spines on apical half, with a distal brush of thick setae (arrow in Fig. 15C); tarsal claw relatively small, without denticles. Leg III (Fig. 15D, F): as leg II except larger and with anterior margin of femur densely covered with thick setae, and posterior margin roundly expanded at apex bearing a group of stout acute spines (Fig. 15F); tibia without distal brush. Coxae I and II directed ventrally, coxae III directed laterally. Abdomen. Gill I reduced in size, double, both portions subequal in length and width. Gills II–VII well developed, ventral portion smaller than dorsal portion; tergum X with well developed ventral spine on posterior margin (not visible dorsally, Fig. 15E). Caudal filaments short (curved in mature nymphs) with whorls of stout spines and simple setae at joinings.

Distribution.

Amazonas and Parana biogeographic subregions (Argentina, Bolivia, Brazil, Colombia, Ecuador, Peru).

Discussion.

The genus Asthenopus has been distinguished by means of the following characters ( Domínguez 1988): 1) ratio foreleg/FW male: 3/5-4/5; 2) male foretarsus 2.5 times longer than foretibia; 3) foretarsal segment 2 similar to the others, and 2/3 the length of tibia); 4) ratio length of Rs stem/fork to margin 1/4 (or fork Rs at 2/10 from base to margin); 5) cubital intercalaries slightly diverging toward hind margin, ICu2 and ICu1 basally fused to CuA by cross veins; 6) ICu2 ending at anal margin or in the tornus, 7) marginal intercalary veins absent; 8) forceps ratio width/length: 1/7; 8) penes robust on basal 2/3; 9) MA fork base to margin 10/100; 11) IMP–MP 1 not fused basally; 12) MP2-IMP similar in length, not fused; 13) foretarsal claws of male not so expanded distally (as in Asthenopodes ). Our phylogenetic analyses only recovered some of these character states as synapomorphies of this genus (see diagnosis and Appendix 2). The proposal of Domínguez (1988) and Hubbard & Domínguez (1988) concerning the intermediacy of Priasthenopus gilliesi with respect to Asthenopus curtus and Asthenopodes picteti is in concordance with our results. Priasthenopus gilliesi resulted sister to the Povilla - Asthenopus clade, presenting some plesiomorphic character states shared with Asthenopodes .

Key to the species of Asthenopus

Male

Female and eggs of Asthenopus species are strongly similar. They may be identified by comparison with co-occurring males. Nevertheless the eggs extracted from female adults or mature nymphs may be keyed as follows:

Nymphs (only 3 species known, almost undistinguishable, the characters below should be confirmed with the study of more material)