Thraulodes sternimaculatus, Lima, Mariano & Pinheiro, 2013

Nascimento, Stênio R. S., Lima, Lucas R. C. & Azevêdo, Carlos A. S., 2019, Description of the nymph of Thraulodes sternimaculatus Lima, Mariano & Pinheiro, 2013 (Leptophlebiidae: Ephemeroptera) from Northeastern Region of Brazil, Zootaxa 4683 (2), pp. 286-290 : 286-289

Thraulodes sternimaculatus ( Figs. 1–15 )

Diagnosis. Male imago: (1) costal membrane basal to bulla without cross veins; (2) costal and subcostal zones of the forewing translucent; (3) one band on femora; (4) abdominal segments in dorsal view predominantly translucent, with three lateral dark spots on terga II–VII; (5) subapical spines of penes short and narrow, apicolateral area not forming an “ear”, lateral pouch present and without recurved folds ( Lima et al. 2013). Nymph: 1) labrum with apical and subapical rows of whitish bristles; anterior margin with three small crenulations and ventrally with a medial, deep excavation; lateral margins rounded ( Figs. 5, 6 ); 2) femur of all legs with sub-apical dark brown band ( Figs. 1,2 , 13–15 ); 3) tarsal claws with seven denticles progressively larger apically tarsal claws with 7 denticles, 4 very small basal and sub-equal in size ( Fig. 12 ); 4) gills lanceolate, tapering abruptly on apical third ward the apex, tapering abruptly toward the apex, with main trachea not branched ( Fig. 4 ).

Mature nymph. Lengths. Body: 6.19 mm. Foreleg: 2.94 mm; middle leg: 3.03 mm; hind leg: 3.58 mm (coxa and trochanter not included). Medial caudal filament: 7.28 mm. Cerci: 5.17 mm.

Coloration ( Figs. 1–4 ). Head: light brown with pale area around eyes; antenna with scape and pedicel dark brown, flagellum yellowish. Eye: upper portion of turbinate eye of male reddish brown, lower portion black, ocelli apically blackish and basally dark brown. Mouthparts: labrum dark brown; mandible dark brown basally, translucent apically (except incisors and molar area both brownish yellow); maxillae yellow translucent, lateral margins dark brown; hypopharynx yellowish brown; labium yellow translucent.

Thorax: pro-, meso-, and metanotum brown with medial line pale light brown. Pronotum light brown with scattered dark brown spots medially; mesonotum dark brown with two light brown longitudinal lines one on each side of medial line; metanotum dark brown with lateral margins light brown. Pronotum light brown; metanotum dark brown. Base of wing pads with two dark brown marks ( Figs. 1, 2 ). Thoracic sterna yellowish.

Legs: pale yellow, all femora with sub-apical dark brown band; tibiae of middle and hind legs whitish, posterior tibia stained medially with light brown ( Figs. 1, 2 ).

Abdomen: segments evenly light brown in dorsal view, except tergum X darker, and terga II–VI with three lateral dark maculae ( Figs. 1, 2 ); sternum pale yellow ( Fig. 3 ). Gills gray and tracheae blackish ( Fig. 4 ). Caudal filaments brownish, basally with blackish annulations on each segment, then alternating every 3-4 segments towards apex ( Figs. 1–3 ).

Morphology. Head: labrum with apical and subapical rows of whitish bristles along anterior margin with medial excavation and three small crenulations ventrally; lateral margins rounded; ventral surface with two median rows of robust median bristles ( Figs. 5–6 ). Mandibles with row of setae on outer margin extending to base of outer incisor; setae long on distal half and short on basal half; molar area with serrated ridges; prosthecae well-developed ( Figs. 7, 8 ); outer incisor of left mandible with three denticles on inner and outer incisors ( Fig. 7 ); outer incisor of right mandible with three apical denticles and inner incisor with two denticles ( Fig. 8 ). Maxilla rectangular, with apical row of long bristles, palpi with few and scattered setae on segments I and II, segment III covered by dense setae. ( Fig. 9 ). Hypopharynx with superlinguae bearing long setae on apical margin; apex of lingua with emargination, ventrally covered by short setae ( Fig. 10 ). Labium densely covered by bristles on glossae and apical third of paraglossae; first segment of palp with both margins bearing long setae; second and third segments with fewer thin setae, concentrated apically ( Fig. 11 ).

Legs: Foreleg: dorsal surface of femur with short and strong spatulate setae medially, inner margin with short spinelike setae, outer margin with simple bristles and spatulate setae of varying sizes; tibia with simple setae on outer margin, short bristles on inner margin with a concentration of short and simple setae at apex; tarsus practically free of simple setae on outer margin ( Fig. 13 ). Middle leg: dorsal surface of femur with short and strong spatulate setae at base, long and simple setae and spatulate setae of varying sizes on outer margin, inner margin with short setae; tibia with simple long setae on outer margin, short spine-like setae and simple setae medially, tarsus with simple setae on outer margin ( Fig. 14 ). Hind leg: femur with short spatulate setae on dorsal surface, spatulate bristles of varying size on outer margin and simple setae at apex, inner margin with short spine-like setae; tibia with simple and long bristles and spatulate setae of varied size on outer margin, short spine-like setae and simple setae on inner margin; tarsus with simple setae on outer margin ( Fig. 15 ). Tarsal claws with seven denticles progressively larger apically. Tarsal claws each with total of seven denticles; four basal denticles very small and sub-equal in size ( Fig. 12 ).

Abdomen: posterolateral spines present on segments III–IX, more evident on segments VI–IX ( Fig. 3 ). Gills lanceolate, tapering abruptly on apical third toward apex, with symmetrical lamellae; main trachea unbranched ( Fig. 4 ).

Biology. The nymphs were collected in a river of moderate current, inhabiting rocks and wood.

Life cycle association. Male imago reared from nymph.

Distribution. Brazil: states of Pernambuco and Piauí. New record for the state of Maranhão: Caxias municipality.

Material examined. One mature male nymph and two male imagos (reared, exuviae mounted on slides), Brazil, Maranhão State, Caxias municipality, Riacho Guarimã, 4°50’02.9”S / 43°29’06.1”W, 16.vi.2018, Nascimento, S. R.S. col. (LEAq).

Comments. Among the seven Brazilian species of Thraulodes known from the nymph, some have little descriptive information and lack illustrations, which makes it difficult to compare structures. The nymphs of T. sternimaculatus have lanceolate gills tapering abruptly towards the apex, with the main trachea not branched, similar to T. bonito . The tarsal claw with denticles progressively larger apically is similar to T. itatiajanus and T. schlingeri ; however, T. sternimaculatus can be distinguished from these species by the color pattern of the legs and abdomen (as in the above description and diagnosis) and details of the labrum with a medial deep emargination, with three small crenulations and lateral margin rounded. The latter character is not observed in other described nymphs from South America.

Figures

FIGURES 1–4. Thraulodes sternimaculatus, nymph. 1, dorsal view; 2, lateral view; 3, detail of abdominal sterna; 4, gill IV. (scale: Figs. 1–2 = 2 mm. Fig. 3 = 1 mm. Fig. 4 = 0.5mm).

FIGURES 5–15. Thraulodes sternimaculatus, nymph. 5, labrum (right, dorsal view; left, ventral view); 6, detail of crenulations on anterior margin of labrum; 7, left mandible; 8, right mandible; 9, maxilla (ventral view); 10, hypopharynx (ventral view); 11, labium (left, dorsal view; right, ventral view); 12, hind tarsal claw; 13, foreleg; 14, middle leg; 15, hind leg. (scale: Figs. 5, 7–11 = 0.5 mm. Figs. 6 and 12 = 0.1 mm. Figs. 13–15 = 1.0 mm).