Acroperus Baird, 1843

Sousa, Francisco Diogo Rocha & Elmoor-Loureiro, Lourdes Maria Abdu, 2019, Identification key for the Brazilian genera and species of Aloninae (Crustacea, Branchiopoda, Anomopoda, Chydoridae), Papéis Avulsos de Zoologia 59, pp. 1-16 : 4-9

Acroperus Baird, 1843 : Oval body, elongated, dorsal

keel present, anterior marginal setae of valves longer than posterior; 1-2 short denticles with wide base on the posteroventral corner of valves. Rostrum triangular shaped, short, not projected;three connected main head pores, tiny lateral head pores; antenna I with two long sensorial setae, one apical and lateral. Postabdomen rel- atively narrow with margins parallel, marginal denticles not developed,short setulae near to base of postabdominal claw, pecten on the postabdominal claw armed with thick spines, basal spine long. Six pairs of limbs; first limb with two setae on the first endite, Inner Distal Lobe (IDL) with three setae: seta 1 long, setae 2-3 armed with setae; exopodite of second limb with a seta; third limb with seven setae on the exopodite; fourth limb with six setae on the exopodite; exopodite of fifth limb bilobed, notch angular between lobes, filter plate with three setae; sixth limb trapezium-shaped.

Comments: Before the description of Acroperus tupinamba Sinev & Elmoor-Loureiro, 2010 , the only species of the genus known for Brazil, this species was treated as the Palearctic Acroperus harpae (Baird, 1835) .

Alona sensu stricto: Oval body, elongated, maximum height at posterior part of body; 7-9 long setulae insert- ed on the posteroventral corner of carapace. Rostrum short, projected in lateral view; labral keel convex, apex with a notch, posterior margin armed two groups of setulae. Posterior part of head shield triangular-shaped, three connected main head pores, tiny lateral head pores; postabdomen relatively massive, dorsal margin rounded, marginal denticles merged, distalmost marginal denticles about 0.6 of basal spine, lateral fascicles with short setulae. Five pairs of limbs; first limb with three setae on the first endite, Inner Distal Lobe with three setae: first seta long, setae 2-3 armed with setulae, setulae of the corm limb not organized in groups; exopodite of second limb armed with long seta setulated on the tip; third limb with seven setae on the exopodite; fourth limb with six setae on the exopodite; exopodite of fifth limb oval, filter plate absent.

Comments: Alona yara Sinev & Elmoor-Loureiro, 2010 , the only species of Alona sensu stricto reported from Brazil. Formerly, this species was treated as the Palearctic Alona quadrangularis (O.F. Müller, 1776) .

affinis -group of Alona sensu lato: Body strongly elongated; 6-8 groups of setulae on the posteroventral corner of carapace. Rostrum short, projected in lateral view; labral keel convex or polygonal, apex without notch,posterior margin with two cluster of setulae. Posterior part of head shield triangular-shaped, two connected main head pores, tiny lateral head pores; the dorsal margin of valve has a tiny pore-like located behind posterior border of head shield. Postabdomen relatively massive, dorsal margin rounded, marginal denticles merged, distalmost marginal denticles about 0.9 of basal spine, with short setulae. Six pairs of limbs; first limb with three setae on the first endite, Inner Distal Lobe (IDL) with three setae: first seta is long, hook-like, setae 2-3 armed with setulae, setulae of the corm limb organized in groups; exopodite of second limb armed with a long seta; third limb with seven setae on the exopodite; fourth limb with six setae on the exopodite; fifth limb oval, filter plate with three setae; sixths limb as an elongate lobe.

Comments: Alona ossiani Sinev, 1998 is the only species of the affinis -group of Alona sensu lato reported from Brazil. This species was formerly treated as Biapertura affinis and Alona affinis (Leydig, 1860) . It is likely that the affinis -group of Alona sensu lato belongs to a new, yet undescribed genus.

intermedia -group of Alona sensu lato: Oval body, maximum height at middle or posterior part of body; 1-3 groups of long setulae on the posteroventral corner of valves. Rostrum short, projected in latera view; labral keel

convex, proximal part armed with a group of short setulae, posterior margin with two clusters of short setulae. Head shield with posterior part triangular-shaped, two connected main head pores. Postabdomen with distal part broadly rounded,marginal denticles merged,setulae of lateral fascicles exceeding the margin of postabdomen, anal margin occupying 60% of postabdomen length. Six pairs of limb: fist limb with three setae on the first endite, Inner Distal Lobe (IDL) with three setae: firs setae relatively long, setae 2-3 armed with setulae; exopodite of second limb armed with a short seta; third limb with seven setae on the exopodite; fourth limb with six setae on the exopodite; exopodite of fifth limb bilobed, filter plate with three setae; sixth limb as an elongated lobe.

Comments: The two species of the intermedia -group of Alona sensu lato that occur in Brazil were treated in literature as Biapertura intermedia (Sars, 1862) or Alona intermedia Sars, 1862 . After its description, the genus Biapertura was considered as another polyphyletic group within the subfamily and fell out of use. It is likely that the intermedia -group of Alona sensu lato may belong to a new, yet undescribed genus.

Key to species of the intermedia -group