Mesocyclops aspericornis (Daday, 1906)

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 : 17-18

Mesocyclops aspericornis (Daday, 1906)

Fig. 20

Diagnosis. Adult female, 1,300 µm in length excluding caudal setae ( Fig. 20A ). Caudal rami about 3 times longer than wide, setules along the entire inner margin; telson has a continuous row of spinules near each caudal rami insertion ( Fig. 20B ). Genital double-somite 1.1–1.3 times longer than wide, without setules ( Fig. 20C ). Seminal receptacle tapering distally in the lateral projections; proximal margin usually sinuous in the middle ( Fig. 20C , arrow). Transverse seminal ducts forming a fused V shape in the copulatory pore; copulatory duct usually strongly curved ( Fig. 20C ). Irregular intervals of 4–10 spinules rows on the distal margin of P4 coxa; 4–11 spinules usually arranged in a single row at the latero-distal angle; proximal row of 4–12 large spinules, and dense outer setulae patch ( Fig. 20D ). Inner apical spine of terminal P4-endopod segment 1.1 times longer than the outer one ( Fig. 20F ). Basis of antenna spinule ornamentation patterns similar to the M. leuckarti - type, a wide field of spinules on posterior margin at the level of the insertion of the median seta, a group of very small longitudinal spinules along the outer margin, and an inner row of longitudinal spinules at irregular intervals, near the concave margin ( Fig. 20G, H ). Anterior face of the antenna basis composed of 17–35 spinules arranged in a longitudinal row along the inner concave margin, transverse row of small spinules on the distal margin, and a transverse row of spinules medially, on the outer margin ( Fig. 20G, H ). Strongly serrulate hyaline membrane on the last segment of antennule, large indentation in its medial portion ( Fig. 20E ) .

Remarks. Collected in the middle stretch of the Paraguay River, which has slow flow and many drifting macrophyte banks. Perbiche-Neves et al. (2014) found this species in the Barra Bonita reservoir, which is the first record of this species for São Paulo state. The species was previously recorded by Reid et al. (1988) in Minas Gerais and Reid (1994) in the Federal District. Reid (1985) stated that this species has been recorded from Colombia, Venezuela, Antilles, Africa, Asia and islands of the Pacific Ocean. It is one of Mesocyclops species considered as a pantropical species ( Holyńska 2000), and present in Australia. Holyńska et al. (2003) mentioned this species from the islands of Sumatra, Singapore, and Hawaii.

Figures

Figure 20. Mesocyclops aspericornis, female: (A) dorsal view of female; (B) dorsal view of caudal ramus; (C) ventral view of genital double-somite, arrow indicates the genital receptacle; (D) P4-intercoxal sclerite, coxa-basis, arrow indicates row of spinules; (E) last segment of antennule, arrow indicates serrated hyaline membrane ornamentation; (F) terminal segment of P4-endopod; (G) basis of antenna, posterior view, arrow indicates a row of spinules; (H) basis of antenna, anterior view, arrow indicates a row of spinules. Scale bars: A–D, F–H = 50 µm, E = 100 µm.