Thermocyclops minutus (Lowndes, 1934)

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 : 40

Thermocyclops minutus (Lowndes, 1934)

Fig. 39

Diagnosis. Adult female, 500 µm in length excluding caudal setae ( Fig. 39A ). Seminal receptacle reaches ¾ of the the genital double—somite length ( Fig. 39B ). Seminal receptacle lateral arms relatively short, with curveted expansion ( Fig. 39B ). P5 terminal spine and seta approximately of the same length ( Fig. 39C ). P4-endopod last segment with sigmoid inner distal spine and longer than the segment, 5 times longer than the outer spine ( Fig. 39D ). Caudal rami 2.5–2.8 times longer than wide, with a small spine at the base of the lateral seta of the caudal ramus ( Fig. 39E ).

Remarks.This species is common in Brazilian reservoirs and has been recorded in many studies. It generally predominates in oligo/mesotrophic waters, a trend observed in recent studies ( Landa et al. 2007, Silva 2011, Perbiche-Neves et al. 2016). The proportion of this species compared to T. decipiens may indicate the trophic status, with a potential high abundance of T. decipiens in more trophic waters. However, this must be carefully evaluated since T.decipiens can also dominate in oligo/mesotrophic waters. Nevertheless, T. minutus is rare in eutrophic waters. This species is small compared to other cyclopoids, and extra care must be taken to avoid confusing it with copepodites of larger species. The curved inner terminal spine and the short outer spine of the third endopodal segment of P4 are useful for the correct identification of this species.

Figures

Figure 39. Thermocyclops minutus, female:(A) dorsal view;(B) ventral view of genital double somite; (C) P5; (D) terminal segment of the P4-endopod, arrow indicates inner terminal spine; (E) dorsal view of the caudal rami, arrow indicates the insertion position of lateral seta and a small spine at base. Scale bars: 50 µm.