Argyrodiaptomus azevedoi (Wright, 1935)

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 : 11

Taxon classification Animalia Calanoida Diaptomidae

Argyrodiaptomus azevedoi (Wright, 1935) Figs 4, 5, 6, 7, 8, 9

Diaptomus azevedoi Wright, 1935

Diagnosis.

Adult male, body length (excluding caudal setae) 1704 µm. Segment 11 of A1R with modified seta about twice length of modified seta on segment 10; segment 13 with long modified seta extending well beyond mid-point of segment 14 (Figs 4D, 5 A–C, G); segment 20 with or without small distal process (cf. Figs 4J and 5E). First endopodal segment of A2 ornamented with pore and patch of spinules (Figs 4L, 5D). Inner margin of left and right BspP5 ornamented with several groups of small spinules (Figs 4E, F, I, K, 6D, E, G). Lateral spine moderately long, about 1/3 length of terminal claw, inserted at outer-distal angle (Figs 4H, 6C). Terminal claw weakly sinuously curved over most of its length, strongly recurved distally (Figs 4 A–C, G, H, 6A). EnpP5 2-segmented (Fig. 6B, F).

Adult female, body length (excluding caudal setae) 1851 µm. Dorsal surface of Ped4 and Ped5 without spinule rows; complete suture present between Ped4 and Ped5; lateral wings slightly asymmetrical, with right wing larger than left; each wing with two sensillae close to postero-distal corner (Fig. 7A). GS asymmetrical, about 1.6 times longer than wide; anterior part weakly swollen, right side more swollen than left (Figs 7A, 8A, H). P5 symmetrical (Figs 7B, 8I), with small conical process at outer distal corner of Cx with strong triangular apical sensilla. BspP5 with short outer seta about 1/3 length of EnpP5. EnpP5 unisegmented, with longitudinal groove (Fig. 8D-E). Exp 3-segmented; lateral spine of Exp2 exceeding length of Exp3 (Fig. 8F); external seta on Exp3 about 1/3 length of internal seta (Fig. 7B); internal seta reaching 2/3 of terminal claw length (Fig. 8F).

Remarks.

In identifying species of Diaptomidae in general, caution must be exercised in using the shape of segment 20 of A1R for species identification because it is often variable within a population. This segment has a falciform process at the distal angle in several species ( Paggi 1976) but, as Wright (1935) points out, in a sample of 25 males of Argyrodiaptomus azevedoi , 11 did not exhibit any process (Fig. 4J) while the remaining 14 carried a short process (Fig. 5E). There is an extensive ornamentation of spinule patches on the surface of the male BspP5 in this species.

Ultrafine-scale ornamentation characters might prove to be valuable in future comparative studies, including 1) the presence of a pore on segment 20 of male A1R (Fig. 5F), 2) the presence/absence of spinules of the basepodite of the A2B in both sexes (Figs 5H, 8C), 3), the presence of a pore on the outer surface of the syncoxa, and of spinules on the distal syncoxal endite of the maxilliped (Figs 5 I–K, 8B), and 4) details of the spinulation on the terminal setae of ExpP4 (Fig. 8G). In the absence of comparable SEM-based data on other species, such data cannot be used for routine species discrimination at present.

This species is widely distributed, extending from northeastern Brazil to the Itaipu Reservoir at the end of the upper Paraná River in southern Brazil (Fig. 9). Typically, few individuals are found in any one sample, so this is not a common species. However, among Argyrodiaptomus , this species is rarely misidentified, given its large body size and distinctive P5.