Microcyclops anceps anceps (Richard, 1897)

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 : 30

Microcyclops anceps anceps (Richard, 1897)

Figs 28 , 29 , 30

Diagnosis. Adult female, 720 µm in length excluding caudal setae ( Fig. 28A ). The distal margin of the second prosomite bears an ornate scalloped membrane, and the other segments have smooth membrane ( Figs 28B , 29B, C ). Caudal ramus 3.1 times longer than wide ( Figs 28C , 29A ). The P1 endopod terminal segment has a pore close to the outer margin in anterior view; P1 endopod terminal spine serrated shape slightly asymmetric compared to Microcyclops finitimus and Microcyclops ceibaensis ( Figs 28D , 30A, B, C ). The inner apical spine on the terminal P4 endopod segment 1.4 times longer than the outer spine ( Fig. 30D ). P5 last segment 2.4 times longer than wide; P5 terminal spine 1.6 times shorter than the width of its segment in the middle portion ( Fig. 30E ).

Remarks. The specimen was collected in the upper stretch of the Paraguay River. Rocha (1998) provided simple and practical characteristics for the identification of five species of Microcyclops that occur in Brazil. Microcyclops anceps is widely distributed in South America ( Dussart and Frutos 1985, José de Paggi and Paggi 2008). Reid (1985) reported it from Brazil, Argentina, Bolivia, Chile, Ecuador, Paraguay, Peru, Uruguay, Venezuela, Central America, and Mexico and Gutiérrez-Aguirre and Cervantes-MartÍnez (2016) examined specimens also from Guyana and Guatemala.

Figures

Figure 28. Microcyclops anceps anceps, female: (A) dorsal view;(B) detail (arrow) of scalloped ornamentation between second and third prosomites; (C) dorsal view of caudal ramus; (D) P1–endopod, pore on surface and terminal spine ornamentation (arrowed). Scale bars: A = 100 µm; B–D = 50 µm.

Figure 29. Microcyclops anceps anceps, female: (A) caudal rami, ventrolateral view; (B) detail of distal margin of the second prosomite, showing a scalloped membrane; (C) cephalothorax in dorsal view, with an ornate scalloped membrane on the distal margin of prosomite 2. Scale bars: A, C = 100 µm; B = 10 µm.

Figure 30. Microcyclops anceps anceps, female: (A) P1 endopod segment, anterior view; (B) left P1 endopod, frontolateral view; (C) detail of surface pore on P1 endopod terminal segment; (D) left P4 endopod last segment; (E) right P5, lateral view. Scale bars: A, B, D, E = 50 µm; C = 20 µm.