Mesocyclops ogunnus Onabamiro, 1957

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 : 23

Mesocyclops ogunnus Onabamiro, 1957

Fig. 25

Diagnosis. Adult female, 1,180 µm in length excluding caudal setae. Genital double-somite 1.2 times longer than wide, seminal receptacle with lateral and posterior expansions ( Fig. 25A ). The last P4 endopod segment 1.1 times longer than the inner terminal spine of this segment; this inner terminal spine not exceeds the outer apical spine length ( Fig. 25B ). Last segment of antennule is ornamented with a narrow, finely serrulate hyaline membrane almost entirely, except to a large subterminal invagination ( Fig. 25C ). Row of spinules in the anterior region of the maxillule palp ( Fig. 25D ). Antenna basis is of the “leuckarti ” type with proximal, medial, and distal rows of spinules; in anterior view a row of spinules on the lateral outer margin and two rows of spinules in the middle of the segment, three rows in the inner margin, and a row of larger spinules on the distal margin, close to the insertion of the terminal setae ( Fig. 25E ). P4 basis with three rows of large spinules in anterior view, two on distal margin and one transverse row close to the outer margin, almost in the middle of the segment ( Fig. 25F ). P4 intercoxal sclerite has small projections on the distal margin. Caudal ramus 2.7 times longer than wide, without setules on the inner margin.

Remarks. Specimen collected in the Rio Grande River, Água Vermelha Reservoir. This species is native from Africa and is now widely distributed in southeastern Brazil. Until now, the records indicate that this invasion began in the upper Paraná River Basin. It may have been introduced with tilapia culture ( Coelho and Henry 2017, Macêdo et al. 2022). More studies are needed to determine its true distribution, whether it is restricted to specific regions, or whether it is limited to the tropics, as it has been found only in southeastern Brazil, not occurring farther south in the La Plata Basin ( Perbiche-Neves et al. 2014). Based on data from Castilho-Noll et al. (2023), this species was found in 43 studies in Brazil, the first dated from 1994 in Furnas Reservoir ( Reid and Pinto-Coelho 1994), followed by 2001 and 2002 in the Upper Paraná River floodplain ( Velho et al. 2001, Lansac-Tôha et al. 2002), and several records were published after 2002 in São Paulo State, especially in reservoirs (e.g., Matsumura-Tundisi and Silva 2002). Custodio et al. (2024) listed 63 records of M. ogunnus in Brazil distributed in 70 articles, and these authors provided models for the distribution of M. ogunnus in the main river basins in Brazil, with potential colonization across the Paraná River Basin, the main watercourses of the Amazon River Basin, and the San Francisco River. The first record in Northeast Brazil was published in 2013 ( Cardôso et al. 2013) and in the Amazon in 2017 ( Silva and Roche 2017). Probably previous records of Mesocyclops kieferi in São Paulo State refer to M. ogunnus , as Matsumura-Tundisi et al. (1990) corrected by Matsumura-Tundisi and Silva (2002), Nogueira (2001), Rocha et al. (2002), Santos-Wisniewski and Rocha (2007), and Sartori et al. (2009), according to Castilho-Noll et al. (2023).

Figures

Figure 25. Mesocyclops ogunnus, female: (A) genital double-somite; (B) terminal segment P4-endopod; (C) last segment of antennule with finely serrate hyaline membrane and a large subterminal invagination (arrowed); (D) maxillule palp, arrow indicates spinule row; (E) Antenna basis spinule ornamentation (arrowed), anterior view; (F) P4 basis. Scale bars: A, C, D, F = 50 µm, B, E = 100 µm.