Caenis
Creators: name: Molineri, Carlos
name: Malzacher, Peter
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy

description: Key to Caenis species from Argentina
Mature nymphs
1. Dark pigments on head present on mediolongitudinal line of occiput (Fig. 166); coxal processes narrow, with smooth margins (Figs. 21–22); tarsal claws I–II with 5–7 very large denticles (Figs. 28–29); operculate gills heavily maculated (Figs. 27, 159, 173) [PA, ARG (Corrientes, Formosa)] ............. C. burmeisteri
1´. Dark pigments on head variable but never present on medial line of occiput (Figs. 165, 167–171); coxal processes more or less elongated, with serrated margins (e.g., Figs. 1–2, 39–40, 127–128); tarsal claws I– II with small denticles or without (e.g., Figs. 3–4); operculate gills not maculated (Figs. 44, 134, 110) or slightly maculated (Figs. 158, 172) ............................................................................................................. 2
2. Small species (body length of male <3.0 mm, female <3.8 mm); general coloration very pale, whitish or yellowish almost without grayish shading (Fig. 162); foretibia with a medial row of long setae, as long or longer than width of tibia (Fig. 130); posteromedian projection of abdominal tergum II short and very broad (Figs. 126, 162); IX sternum with a deep V-shaped notch at hind margin and with very short lateral spines (Fig. 135 a–b) [URU, ARG (Formosa, Misiones, Buenos Aires)] ................................... C. tenella
2´. Medium to large species (male length> 3.5 mm, female> 4.1 mm); general coloration darker, yellowish brown to dark brown with grayish markings (Figs. 158, 160–161, 163–164); foretibia only with short setae (Fig. 83); posteromedian projection of abdominal tergum II longer and narrower (e.g., Fig. 48); hind margin of IX sternum rounded, truncate or with an U-shaped indentation, lateral spines longer and stronger (e.g., Fig. 49) ......................................................................................................................................... 3
3. Occiput without submedian marks (Fig. 167); operculate gills only with simple setae dorsally (Fig. 44). 4
3´. Occiput at least with a pair of submedian star-like dark markings (Figs. 165, 168–171); operculate gills with simple setae and plumose or scale-shaped microtrichia1 dorsally (e.g., Figs. 6, 74)........................... 5
4. Abdominal sternum IX with a median U-shaped indentation on posterior margin (Fig. 49) [BO, ARG (Córdoba, Catamarca, Santiago, Salta)] ................................................................................ C. dominguezi
4´Abdominal sternum IX with straight or slightly rounded posterior margin [CHI, ARG (Neuquén, Río Negro)] ........................................................................................................................................... C. gonseri
5. Dorsal surface of body and operculate gills with large, scale-shaped microtrichia (Figs. 8 i-j in Malzacher 2001); lateral margin of segment IX, besides short and apically frayed spines, with small teeth (Fig. 8 l in Malzacher 2001) [BRA, ARG (Misiones)] .............................................................................. C. plaumanni
5’. Dorsal surface of body and operculate gills without or with small ramified or bifurcate microtrichia (Figs. 6, 74, 116); lateral margin of segment IX without small teeth .................................................................... 6
1. Microtrichia can only be seen under high magnification (e.g., x100–x400) 6. Hind margin of the head with relatively long, laterally directed setae; abdominal sterna with blackish sublateral spots and other distinct marks (Fig. 179); coxal processes short, semicircular or semielliptical (Figs. 1–2) [ARG (Buenos Aires, Santiago, Catamarca, Tucumán)] ........................................ C. argentina
description: Published as part of Molineri, Carlos & Malzacher, Peter, 2007, South American Caenis Stephens (Ephemeroptera, Caenidae), new species and stage descriptions, pp. 1-31 in Zootaxa 1660 on page 3, DOI: 10.5281/zenodo.179923