Eucyclops serrulatus serrulatus (Fischer, 1851)

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 : 14

Eucyclops serrulatus serrulatus (Fischer, 1851)

Figs 14 , 15

Diagnosis. Adult female, 1,390 µm in length excluding caudal setae. Caudal ramus 5 times longer than wide ( Fig. 15A, D, E ); row of spines extending over half or up to the entire outer margin of the caudal ramus ( Figs 14A, D , 15D, E ). Seminal receptacle ducts horizontally divided into two parts ( Fig. 14B ). P5 middle seta 1.8–1.9 times longer than the inner spine ( Figs 14C , 15B, C ). Inner spine of the terminal P4-endopod segment 1.2 times shorter than the outer spine ( Fig. 12D ).

Remarks. Species with a wide geographic distribution in the Americas, often found in coastal regions, aquatic macrophytes and rivers. It is seldom found in pelagic regions of reservoirs or lakes. Animals dark or brown-colored and usually with debris attached to the body segments and appendages, due to the benthic or littoral habit. This species can be distinguished from the other congeners by the proportions of the caudal rami and the extent of the spinules along the outer margin. The division of the genital double-somite and the proportions of the spines and setae on the P5 are also distinctive characters. Possibly, a complex of cryptic or semi-cryptic species is hidden under similar morphologies.

Figures

Figure 12. Eucyclops prionophorus, female: (A) genital double-somite, ventral view; (B) caudal rami; (C) P4 right, anterior view; (D) P4 left, anterior view. Scale bars: A, C, D = 50 µm; B = 100 µm.

Figure 14. Eucyclops serrulatus serrulatus, female: (A) caudal ramus and caudal setae; (B) genital double-somite, seminal receptacle in the middle; (C) P5; (D) P4 terminal endopod; (E) caudal ramus. Scale bars: A, B, E = 100 µm; C = 100 µm.

Figure 15. Eucyclops serrulatus serrulatus, female: (A) habitus, ventrolateral view; (B) P5; (C) prosomite 5 and genital double-somite in lateral view, showing P5 (indicated by arrow); (D–E) caudal rami. Scale bars: A = 500 µm; B = 20 µm; C = 50 µm; D, E = 100 µm.