Caenis marataoan Nascimento & Lima sp. nov.

(Figs 2A–E, 3A–E, 4A–C, 5A–C).

Diagnosis. This species can be characterized by the following combination of characters in the imagos: 1) male body length 1.5–2.0 mm, female body length 2.5–2.8 mm; 2) base of antennal flagellum not dilated; 3) forceps apically rounded, covered with trichomes, with 2–3 minute spines at apex (Figs 2B–E); 4) styliger plate short with posterior margin convex (Fig. 2A); 5) penis square-shaped, fused and not laterally projected; ventral surface without tubercles and groove (Fig. 2A); 6) eggs oval-shaped; micropyle linear with narrow and long micropylar canal, preceded by an oval sperm guide (Figs 5A, B).

Description. Male imago. Body length: 1.5–2.0 mm; forewing: 1.4–1.8 mm; foreleg: 1.4–1.5 mm; hind leg: 0.8–1.1 mm; cercus: broken off.

Ratios. Foreleg 1.2–1.8 × the length of hind leg. Ratio of first segment of the foretarsus length to 2 nd:3 rd:4 th:5 th = 0.2:0.3–0.4:0.3–0.5:0.5–0.7. Genitalia: forceps length 2.7–3.5 × the width at half length; distance between the extreme lateral points of the forceps bases to forceps length = 2.3–3.0.

Coloration. Head: whitish shaded with gray in dorsal view (Fig. 2A); venter of head whitish (Fig. 2C). Antenna: scape and pedicel whitish, flagellum hyaline (Figs 2A–C). Thorax. Prothorax yellowish translucent shaded with gray on lateral and posterior margin (Figs 2A–D). Meso- and metanotum yellowish shaded with gray on carinae; mesonotum yellowish; pleurae and sterna paler. Wing membrane hyaline, veins translucent except C, Sc and Rs grayish. Legs. Foreleg whitish translucent with coxa and femur shaded with gray. Middle and hind legs whitish translucent. Abdomen. Abdominal segments I–VIII translucent white, IX–X yellowish; abdominal terga I–II with a blackish line on posterior margin (Figs 2A, E). Sterna translucent white with segments IX–X yellowish (Fig. 2C). Pleura white (Fig. 2B). Genitalia. Sternum IX with weak and uncolored sclerites (Fig. 2C). Forceps, penis and caudal filaments translucent white (Figs 2B, C).

Morphology. Antenna: Base of antennal flagellum not dilated. Thorax. Lateral margins straight, not protruding; prosternal longitudinal ridges forming a triangle shaped structure, open anteriorly and with straight lateral margins (Fig. 2A). Abdomen. Lateral filaments and finger-like process on tergum II lacking. Genitalia. Styliger plate rectangular, not sclerotized, covering the basal 2/3 of penis; anterior margin almost straight and posterior margin slightly convex; central sclerite circular, apophyses short and pointed, basolateral and lateral sclerites weakly discernible (Fig. 3A). Forceps, apically rounded, densely covered with trichomes, and not fused to lateral margins of styliger plate (Figs 3A–E). Penis square-shaped, fused and not laterally projected; ventral surface without tubercles and groove (Fig. 3A).

Female imago. Body length: 2.5–2.8 mm; forewing: 2.2–2.3 mm; foreleg: 1.4–1.8 mm; cercus: broken off. Thorax: same as males except dark lines on sutures of mesonotum (Fig. 4A); katepisternum not paler than rest of mesopleural sclerites (Fig. 4B). Abdomen: same as males except abdomen with segments I–VI shaded with gray; abdominal sternum IX with posterior margin straight, not projected (Fig. 4A, C). Lateral filaments absent.

Egg. Length: 102–114 μm; width: 62–68 μm. Coloration light yellow. Oval-shaped with length 1.7–1.9 × width. Chorion surface with small pores. Micropyle linear with narrow and long micropylar canal, preceded by an oval sperm guide (Figs 5A, B). Two polar caps hood-like (multithread with short filaments and small knobs). (Figs 5A, C).

Nymph. Unknown.

Etymology. The specific epithet is given to this species as a noun in apposition, and refers to the Marataoan River, type locality of the new species.

Type material. Holotype: one ♂ imago (genitalia on slide) from Brazil, Piauí State, Barras municipality, Marataoan River, Pesqueiro, S4°15’13.7”, W42°17’19.1”, 84m, 18.iv.2017, Lima, L. R.C. col. (INPA-EPH000030) . Paratypes: 75 ♂ imagos (light trap), same data as holotype (INPA-EPH000031); eight ♂ imagos and two ♀ imagos (light trap), same data as holotype except 10.x.2015 (INPA-EPH000032). Two ♂ imagos (light trap) from Brazil, Piauí State, Batalha municipality, Longá River, Cachoeira do Urubu, Pedra Dela, S3°54’51.7”, W42°06’37.8”, 68m, 10.x.2015, Lima, L. R . C. col. (UFVB000425) . 15 ♂ imagos (light trap), from Brazil, Piauí State, Barras municipality, Longa River, near the PI-113 brigde, S4°12’08.4”, W42°14’21.2”, 74m, 18.iv.2017, Lima, L. R . C. col. (UFVB000426) .