Caenis tenella (Navas) Navas, 2007

Molineri, Carlos & Malzacher, Peter, 2007, South American Caenis Stephens (Ephemeroptera, Caenidae), new species and stage descriptions, Zootaxa 1660, pp. 1-31 : 21-24

publication ID	https://doi.org/ 10.5281/zenodo.179923
DOI	https://doi.org/10.5281/zenodo.6244721
persistent identifier	https://treatment.plazi.org/id/03E91135-4F36-E600-FF02-837682DCFCEE
treatment provided by	Plazi
scientific name	Caenis tenella (Navas)
status	comb. nov.

Treatment

Caenis tenella (Navas) View in CoL comb. nov. ( Figs. 123–138 View FIGURES 123 – 138 , 147–148 View FIGURES 139 – 157 , 162 View FIGURES 162 – 164 , 168, 176, 182)

Eurycaenis tenella Navas, 1932a: 112 (male, female)

Brachycercus tenella ; Thew, 1960: 202; Domínguez et al., 2006: 197 Brachycercus tenellus ; Soldán, 1986: 294

Caenis grimi Malzacher, 2001: 15 (male, female, eggs) syn. nov.

Type material. Eurycaenis tenella : holotype male imago and allotype female imago ( MUNSA) from ARGENTINA : Buenos Aires, San Miguel, 9-XII-1932 and 3-XI-1931, Williner S. J. col. Caenis grimi : holotype male imago ( IFML) from ARGENTINA : Formosa, Laguna Yema, S 24° 22' – W 61° 09', 11-XI-1985, E. Domínguez col.; 50 paratypes imagos of both sexes, data as holotype.

Additional material. One reared male subimago and nymphal exuviae from ARGENTINA : Misiones, P.P. Urugua-í, arroyo Uruzú , S 25º 51' – W 54º 10', 322 m, 7-11-XII-1999, C. Molineri col.; 3 male imagos and 1 nymph Misiones, San Pedro, confluencia ríos Alegría y Pirai-Guazu, 22-23-XI-1998, E. Domínguez et al. cols.; 11 female imagos Misiones, 25 km S El Soberbio, 21-XI-1998, E. Domínguez et al. cols.; 1 nymph, 1 male and 2 female imagos Misiones, Candelaria, 2 km E Bonpland, río del Camping, 15-II-1985, E. Domínguez col.; 1 male and 7 female imagos Misiones, Mado, 16-II-1985, E. Domínguez col.; 5 male and 5 female imagos Misiones, 10 km NE de San Vicente, INTA Cuartel Victoria, 30-XI-1986, E. Domínguez col.; 1 nymph Misiones, Puerto Mado, arroyo Yacutinga, 19-20-XI-1998, E. Domínguez et al. cols.; 11 male and 3 female imagos Misiones, P.N. Iguazú, 26-XI-1998, río Iguazú, Puerto Canoas, Domínguez, Molineri & Nieto cols.; 9 male and 15 female imagos Misiones, 10 km NE de San Vicente, INTA Cuartel Victoria, 20-XI-1998, E. Domínguez et al. cols.; 6 male and 20 female imagos URUGUAY: Salto Arapey, 4 km de Las Termas, Carbonell col.; 2 male and 2 female imagos Cerro Largo, arroyo Quebracho (curso superior), 4-8-III-1959, Carbonell col.; 30 male and 30 female imagos Tacuarembó, arroyo Laureles, 10-XI-1954, Carbonell col.; 50 female adults Salto, Paso Yacaré, arroyo Itapebi, Zolessi et al. cols. BRAZIL: 3 nymphs, Nova Teutonia, 100 km E. Cacado, S 27° 11' – W 52° 23', III-1962; 1 nymph, Seara, S 27° 09' – W 52° 15', 18-IV-1962; 2 nymphs, Tupitinga, Santa Cruz Riv., S 27° 30' – W 51° 12', XII-1962; Rio Grande do Sul, Arroio do Hilario, S 30° 43' – W 53° 30', XI-1964. All the material in IFML, except 20 male and 50 female imagos in MCFU and nymphs from Brazil in col. Malzacher.

Imagos. Navas (1932a) descriptions are uninformative, but Malzacher (2001) give a complete treatment of male and female imagos (as C. grimi ).

Mature nymph ( Fig. 162 View FIGURES 162 – 164 ). Length of female: body, 3.8 mm; caudal filaments, 2.5–2.8 mm; length of male: body, 2.7 mm; caudal filaments, 2.0 mm. General coloration yellowish to brownish. Head shaded gray on occiput and between antennae (Fig. 168), stronger on a transverse band behind lateral ocelli; venter of head paler than dorsum; antennae whitish, with strong setae on scape and pedicel; hind margin of the head with short bifid setules. Mouthparts: clypeus ( Fig. 123 View FIGURES 123 – 138 ) with strong setae directed posteriorly, labrum as in Fig. 123 View FIGURES 123 – 138 , sometimes with small bifid setae; labium ( Fig. 124 View FIGURES 123 – 138 ) with short and conic distal segment on palpi (segment II of labial palp 1.80–2.43 times the length of segment III), and large subquadrate glossae. Thorax. Pro- and mesonotum brownish-yellow with pale blotches, with very few grayish markings. Anterolateral margin of pronotum rounded and with setae ( Fig. 125 View FIGURES 123 – 138 ). Wingbuds shaded with gray on posterior half. Metanotum whitish. Legs ( Figs. 130–132 View FIGURES 123 – 138 ): forelegs yellowish, middle and hind legs whitish; shaded with gray on coxae; coxal projections rounded with serrated margin ( Figs. 127–128 View FIGURES 123 – 138 ); fore femora with subdistal transverse row of dorsal

setae ( Figs. 129–130 View FIGURES 123 – 138 ), middle and hind femora with few dorsal setae, mainly along posterior margin ( Figs. 131–132 View FIGURES 123 – 138 ); fore tarsus with one row of robust simple setae; middle tarsus with one row of serrated setae; hind tarsus with one row of simple setae and one row of serrated setae; tarsal claws with small denticles, more numerous on hind claws ( Figs. 136–138 View FIGURES 123 – 138 ), apex moderately to strongly curved. Abdomen whitish with yellowish zones on median projection of tergum II, lateral zones of terga VII–IX, and on tergum X ( Fig. 176 View FIGURES 172 – 178 ); median projection of abdominal tergum II small ( Fig. 126 View FIGURES 123 – 138 ). Abdominal sterna whitish without marks ( Fig. 182 View FIGURES 179 – 184 ). Posterolateral pointed projections on abdominal segments III–IX. Abdominal gill II ( Fig. 134 View FIGURES 123 – 138 ) yellowish translucent very slightly shaded with gray, dorsum only with simple setae, stout setae ( Fig. 133 View FIGURES 123 – 138 ) present on the ventral submarginal row; gills III–VI shaded completely with grayish, with a blackish spot at the base (visible through operculate gills, Fig. 176 View FIGURES 172 – 178 ). Sternum IX apically with a deep V-shaped notch ( Fig. 135 View FIGURES 123 – 138 ) and with bifid setules on hind margin. Cerci whitish.

Diagnosis. Caenis tenella can be distinguished from the other species of Caenis by the following combination of characters. In the imago: 1) general coloration whitish-yellow; 2) prosternal triangle anteriorly elongated, pointed to slightly rounded in males, somewhat wider and rounded apically in females; 3) median filament on abdominal tergum II absent; 4) fore legs 0.5–0.6 times length of body; 5) forceps apically rounded; 6) central sclerite of styliger dome-shaped; 7) apophyses of styliger sclerite bent inwards; 8) penes with projected and pointed lateral lobes; 9) color of katepisternum similar to the rest of thoracic sclerites. In the nymph: 1) head color pattern as in Fig. 168, hind margin with short bifid setules; 2) meso- and metacoxal processes present but small ( Figs. 127–128 View FIGURES 123 – 138 ); 3) middle tarsus generally with one row of serrated setae; 4) tarsal claws with small denticles, apex curved ( Figs. 136–138 View FIGURES 123 – 138 ); 5) labrum with slightly rounded lateral margins, clypeus with strong setae ( Fig. 123 View FIGURES 123 – 138 ); 6) labial glossae large and subquadrate ( Fig. 124 View FIGURES 123 – 138 ), segment II of labial palp 1.80–2.43 times the length of segment III ( Fig. 124 View FIGURES 123 – 138 ); 7) lingua of hypopharynx relatively large and with concave fore margin ( Fig. 157 View FIGURES 139 – 157 ); 8) IX sternum apically with a deep V-shaped notch and with bifid setules on hind margin.

Discussion. Navas (1932) described this species from a pair of imagos of both sexes. As the types have been lost, serious doubts about the identity of the species existed ( Thew 1960, Soldán 1986, Domínguez et al. 2006), but the pinned holotype and allotype of Eurycaenis tenella Navas (1932) were recently discovered in Salta ( Argentina ). The examination of these types and those of Caenis grimi Malzacher (2001) , showed that both species are the same, and are here proposed as subjective synonyms. Thus the new combination Caenis tenella (Navás) is created to accommodate this species.

Distribution ( Fig. 186). Argentina ( Formosa, Misiones, Buenos Aires), Uruguay, Brazil (Rio Grande do Sul).