Argyrodiaptomus falcifer (Daday, 1905)

Perbiche-Neves, Gilmar, Boxshall, Geoffrey Allan, Previattelli, Daniel, Nogueira, Marcos Gomes & da Rocha, Carlos Eduardo Falavigna, 2015, Identification guide to some Diaptomid species (Crustacea, Copepoda, Calanoida, Diaptomidae) of " de la Plata " River Basin (South America), ZooKeys 497, pp. 1-111 : 17

Taxon classification Animalia Calanoida Diaptomidae

Argyrodiaptomus falcifer (Daday, 1905) Figs 15, 16, 17, 18, 19

Diaptomus falcifer Daday, 1905

Diaptomus argentinus Wright, 1938

Argyrodiaptomus argentinus (Wright, 1938)

Diagnosis.

Adult male, body length 1495 µm. Ur4 with patches of fine spinules on dorsal surface (Fig. 15 A–B). Inner margin of CR with setules, outer margin smooth. Modified seta of segment 13 of A1R short, not reaching beyond tip of spinous process on segment 14; spinous process of segment 14 well developed (Fig. 16A, C, E); spinous process of segment 15 of A1R shorter than spinous process of segment 14 (Fig. 15F); segment 20 of A1R typically with falciform process; falciform process variable, when present can attain length up to half length of segment (Fig. 16B, D, F). Right BspP5 approximately 1.5 times longer than wide (Fig. 15D), ornamented with few spinules, lacking spinules in many specimens; left BspP5 approximately 2.5 times longer than wide, with 5 patches of spinules (Figs 15G, 16G, H). Lateral spine of right Exp2P5 about 40% of length of terminal claw (Fig. 15E).

Adult female, body length 1648 µm. Dorsal surface of pedigers lacking ornamentation of spinules (Fig. 18 A–C). Complete suture present between Ped4 and Ped5; lateral wings slightly asymmetrical (Fig. 17A); both wings with two sensillae each, one at distal corner. GS weakly asymmetrical, approximately 1.5 times longer than wide (Fig. 18B). Anterior of GS slightly swollen. P5 symmetrical, with small conical process at outer distal corner of Cx, bearing short triangular sensilla with bifid apex (Fig. 17B). BspP5 with short outer seta, less than half length of outer margin of Exp1P5. EnpP5 2-segmented but with incompletely-expressed transverse articulation and longitudinal groove (Figs 17C, 18D, E). ExpP5 3-segmented; lateral spine of Exp2P5 reaching about to midlength of external margin of Exp3P5 (Fig. 18F); external seta of Exp3P5 about 3/4 length of internal seta; internal seta about half length of terminal claw (Fig. 18 G–H).

Remarks.

The specimens illustrated here were caught in the middle stretch (RPAR-M2) of the Paraná River, and the sample contained only a few females and two males. Paggi (2006) provided a redescription and confirmed the validity of Argyrodiaptomus falcifer , recognizing at the same time that Argyrodiaptomus argentinus (Wright, 1938) should be treated as a junior subjective synonym of this species. Paggi also summarized its geographical distribution across Argentina and Paraguay. Previattelli (2006) also illustrated this species, but he considered this taxon under the binomen Argyrodiaptomus argentinus .

This species, together with others of this genus, can be very abundant in small scale habitats, such as water pools, and is generally scarce in lotic environments. It was found at only three stations in the present study (Fig. 19).