Tropocyclops prasinus meridionalis (Kiefer, 1931)

Perbiche-Neves, Gilmar, Corgosinho, Paulo H. C., Previattelli, Daniel, Suárez-Morales, Eduardo, Nogueira, Marcos G. & da Rocha, and Carlos E. F., 2025, Catalogue for identification of the most common lacustrine and riverine cyclopoid copepod (Crustacea) species in plankton of La Plata Basin, South America, Zoologia (e 24023) 42, pp. 1-47 : 41-43

Tropocyclops prasinus meridionalis (Kiefer, 1931)

Fig. 40 Diagnosis. Adult female, 500 µm in length excluding caudal setae ( Fig. 40C ). Genital double-somite 1.6 times longer than wide; seminal receptacle with two horizontal projections ( Fig. 40A ). Caudal ramus 1.7–2.1 times longer than wide ( Fig. 40B ). The P5 inner seta and the outer spine has approximately the same length ( Fig. 40D ). The P4-endopod outer terminal spine is slightly less than half the length of the inner terminal spine ( Fig. 40E ).

Remarks. This species is common in reservoirs and other lentic environments (pools, ponds, lakes, burrows) of Brazil and Argentina, and occurs in ephemeral environments where few species can survive, such as very warm waters or areas susceptible to freezing, or in ponds rich in humic acids in Amazonia. This species occurs from latitude 3°N in Brazil (Perbiche-Neves unpublished data) to southern Argentina ( Menu Marque 2001). It can be dominant in eutrophic reservoirs, if conditions are unfavorable for other species. Due to its small size, it may be mistaken for a copepodite. Tropocyclops prasinus meridionalis may co-occur with T. prasinus prasinus , but in the latter species, the caudal rami tend to be slightly longer than in T. prasinus meridionalis 0In addition, there are differences in the terminal outer and inner spine length of the P4-endopod segment, according to Reid (1985). The T. prasinus complex requires an urgent worldwide revision.

Figures

Figure 40. Tropocyclops prasinus meridionalis, female: (A) genital double-somite; (B) caudal ramus; (C) habitus, dorsal view; (D) P5; (E) terminal segment of P4 endopod. Scale bars: A, B, D, E = 50 µm, C = 100 µm.