Mesocyclops ellipticus Kiefer 1936

Mesocyclops ellipticus Kiefer, 1936 Fig. 21 Diagnosis. Adult female, 960 µm in length excluding caudal setae (Fig. 21A). Setules on inner margin of caudal rami (Fig. 21B). Genital double-somite 1.0–1.2 times longer than wide, seminal receptacle with very narrow elliptical ducts expanding horizontally (Fig. 21C). Ornamentation of P4-coxa in posterior view composed of 5 or 6 groups of spinules; with one proximal row in the middle, one inner row (close to the intercoxal sclerite) medially on the segment, two spinules rows on the distal outer margin and one row on the distal inner margin; occasionally, individual spinules also occur in the middle portion (Fig. 21D). P5 terminal seta slightly longer than the inner spine and the outer seta of the anterior segment (Fig. 21E). P4 endopod outer terminal spine 1.1 times longer than the inner one (Fig. 21G). Terminal segment of the antennule with a finely serrulate hyaline membrane (Fig. 21F). Antenna basis with row of spinules on the inner concave margin in anterior and posterior views in a similar trend, slightly smaller spines in the proximal and distal regions and larger spinules in the middle, giving a semi elliptical shape to this ornamentation (Fig. 21H, I). Remarks. In this study, this species was found only in the upper stretch of the Paraguay River, which has a slow flow and many drifting aquatic macrophyte banks, especially Eichhornia sp. Holyńska et al. (2003) mentioned that this species occurred in small puddles (type locality is Bom Conselho, Pernambuco, Brazil) and in large lakes such as Lake Maracaibo in Venezuela, and these authors mentioned a variation for the P4 terminal endopod inner spine between 0.9–1.2 times than the outer one. In Brazil, Perbiche-Neves et al. (2014) found this species in the eutrophic Barra Bonita Reservoir, contrasting with the suggestions by Dussart (1984) and Rocha and Botelho (1998) that this species prefers oligotrophic waters. Probably the association with macrophytes is valid. This species is easily recognizable by the elliptical seminal receptacle, the basis of the antenna, and the P4 coxa. It can be confused with Mesocyclops reidae, but this latter species has been recorded only in Central America and southern North America.