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, 5A–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 4A–C, G, H, 6A). EnpP5 2-segmented (Fig. 6B, F).

Figure 4. 

Argyrodiaptomus azevedoi male. A, B, C Different views of Right P5 D Segments 12, 13 and 14 of A1R E, F Different views of Left P5, showing details of spinular ornamentation G Right Exp2P5 H Right P5 I Basal segments of right and left P5 J Segments 20, 21 and 22 of A1R K Detail showing spinules on BspP5R L Endopod of A2, showing pore and spinular ornamentation.

Figure 5. 

Argyrodiaptomus azevedoi male, SEM photographs. A Geniculate right antennule (500 µm) B Segments 12–17 of A1R (300 µm) C Segments 13–14 of A1R (100 µm) D Enp of A2, showing pore and spinular ornamentation (50 µm) E Segments 20–22 of A1R (100 µm) F Inset showing pore on segment 20 of A1R (5 µm) G Segments 12–16 of A1R (100 µm) H A2 (200 µm) I Maxillipeds (200 µm) J Distal endite of maxilliped (50 µm) K Maxilliped (200 µm).

Figure 6. 

Argyrodiaptomus azevedoi male, SEM photographs. A P5R (100 µm) B P5L and P5R (200 µm) C P5R (200 µm) D P5L (100 µm) E P5L (50 µm) F EnpP5R (20 µm) G BspP5L, showing ornamentation of spinules (50 µm).

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).

Figure 7. 

Argyrodiaptomus azevedoi female. A Dorsal view of Ped4 and Ped5 and GS B P5R.

Figure 8. 

Argyrodiaptomus azevedoi female, SEM photographs. A Ventral view of fifth pediger bearing P5, and GS with eggs attached (200 µm) B Distal endite of maxilliped (50 µm) C Detail of spinules on basis of antenna (50 µm) D P5L (50 µm) E P5R (50 µm) F Distal part of ExpP5R (50 µm) G Apical spine of Enp3P4 (100 µm) H Genital area (fertilized female) on ventral surface of GS (50 µm) I P5 (100 µm).

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 A. 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 5I–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.

Figure 9. 

Geographical distribution of A. azevedoi in de la Plata river basin.

Adult male, body length 1657 µm. Dorsal surface of Ped5 ornamented with irregular rows of spinules (Figs 10D, 11A). Ur4 with rows of spinules on dorsal surface. Antennules (Fig. 11D) long, reaching beyond posterior margin of Ur2 but not exceeding CR. Modified seta of segment 13 of A1R with acute apex and reaching middle of segment 14 (Figs 10A, 11C); spinous process on anterior margin of segment 15 always present and well developed, slightly curved. Segment 20 typically with long, curved distal process (Figs 10C, 11B). Enp1A2 with row of spinules on dorsal margin and single pore. BspP5R with proximal expansion on internal margin, overlapping BspP5L (Fig. 10B); BspP5R ornamented with small spinules on surface of rounded distal process on inner margin; inner surface of BspP5L with spinules. Exp2P5 ornamented with minute spinules on process on outer margin proximal to insertion of lateral seta (Fig. 11E–H).

Figure 10. 

Argyrodiaptomus denticulatus male. A Segments 13–16 of A1R, showing spinous processes on segments 13 and 15 (arrowed) B Complete P5, showing proximal lobe on right Bsp overlapping margin of left Bsp C Segment 20 of A1R D Part of boundary between Ped4 and Ped5, showing ornamentation of dorsal spinules.

Figure 11. 

SEM photographs. Argyrodiaptomus denticulatus male. A Dorsolateral view of right side of Ped4 and Ped5 (100 µm) B Segment 20 of A1R (100 µm) C Segments 11–15 of A1R (200 µm) D A1R (500 µm) E P5R (200 µm) F, G Detail showing spinular ornamentation on process at base of lateral spine of Exp2P5R (F = 10 µm; G = 10 µm) H Right P5 (200 µm).

Adult female, body length 1753 µm. Spinules present dorsally along posterior margins of Ped3 and Ped4 (Fig. 13A). Complete suture present between Ped4 and Ped5. Lateral wings on Ped5 slightly asymmetrical, left wing longer than right; both wings projecting posteriorly, carrying two sensillae each, one at postero-distal corner (Fig. 13B). GS slightly asymmetrical, about twice as long as wide and slightly swollen anteriorly (Fig. 12A). P5 symmetrical (Fig. 12B), with small conical process at outer distal corner of Cx, bearing short triangular sensilla, bifid apically. BspP5 with short external seta, approximately one third length of Exp1P5. EnpP5 2-segmented, with two apical setae and distal row of spinules (Fig. 12B, C). ExpP5 3-segmented; lateral spine of Exp2P5 short, extending only to middle of Exp3P5; internal seta of Exp3P5 reaching beyond middle of terminal claw (Fig. 13E); external seta of Exp3P5 about 1/4 length of inner seta; terminal claw with two rows of 10–15 strong spinules (Fig. 13C–D).

Figure 12. 

Argyrodiaptomus denticulatus female. A Dorsal view of posterior pedigers and GS B Complete P5 C Lateral view of left P5, with enlargement showing EnpP5.

Figure 13. 

Argyrodiaptomus denticulatus female, SEM photographs. A Dorsolateral view of Ped4 and Ped5, showing ornamentation of spinules (200 µm) B Lateral wings on left side of Ped5, showing sensilla at apex of each projection (100 µm) C Left terminal claw (50 µm) D Right terminal claw (50 µm) E Lateral view of P5 (100 µm).

The male illustrated was collected from the Salto Grande reservoir (SGRA-D), Uruguay River. The female illustrated here belongs to the collection of the Museo Argentino de Ciencias Naturales (Buenos Aires) (MACN-In 29733), and was examined because of the scarcity of females in the samples from de la Plata river basin. This species can be readily identified because of the distinctive structure of its P5 and the presence of dorsal rows of spinules on the male pedigers, which are lacking in other species of Argyrodiaptomus.

This species is common in the lower regions of the basins of the Paraná and Uruguay rivers (Figure 14), and has been reported in several studies, particularly by Argentinian researchers. Santos-Silva (2008) recorded this species in southern Brazil, in the state of Rio Grande do Sul. Previattelli et al. (2013) included a record of this species from Bolivia, a distance of about 1,300 km north of the previous northernmost record. It is possible that the distribution of this species extends beyond this northern limit to at least the line of latitude 35°, but verification is needed.

Figure 14. 

Geographical distribution of A. denticulatus in de la Plata river basin.

Adult male, body length 1495 µm. Ur4 with patches of fine spinules on dorsal surface (Fig. 15A–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).

Figure 15. 

Argyrodiaptomus falcifer male. A Ped4, Ped5, and urosome somites B Details of ornamentation of spinules dorsally on Ur4 C Segments 1–11 of A1R D Complete P5 E P5R in caudal view F Segments 12–17 of A1R G P5L, showing spinular ornamentation on Bsp.

Figure 16. 

Argyrodiaptomus falcifer male, SEM photographs. A Segments 12–15 of A1R, showing detail of spinous process on segment 14 (arrowed) (100 µm) B Entire A1R (500 µm) C Segments 11–15 of A1R (100 µm) D Adult male, lateral view (1000 µm) E Spinous processes on segments 13 and 14 A1R (20 µm) F Segment 20 of A1R, showing falciform process (50 µm) G Complete P5, caudal view (200 µm) H Medial surface of BspP5L, showing spinular ornamentation (50 µm).

Adult female, body length 1648 µm. Dorsal surface of pedigers lacking ornamentation of spinules (Fig. 18A–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. 18G–H).

Figure 17. 

Argyrodiaptomus falcifer female. A Dorsal view of last two pedigers of prosome, GS and CR B P5 C EnpP5L.

Figure 18. 

Argyrodiaptomus falcifer female, SEM photographs. A Dorsal view (1000 µm) B Ped4, Ped5, and GS (150 µm) C Ped4, Ped5, and GS D EnpP5R (20 µm) E EnpP5L (20 µm) F ExpP5L (100 µm) G P5 (100 µm) H ExpP5L (100 µm).

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 A. 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).

Figure 19. 

Geographical distribution of A. falcifer in de la Plata river basin.

Adult male, body length 1354 µm. Modified seta of segment 13 of A1R with bifid apex, reaching or exceeding proximal border of segment 14 (Fig. 20K); spinous process on anterior margin of segment 15 present, or sometimes absent; distal process of segment 20 sometimes absent, if present, variable from short (Fig. 20G) to strong, long and curved (Fig. 21A, C, D). Basipodite of A2 with spinular ornamentation (Fig. 21B, I); Enp1A2 with row of spinules and single pore (Fig. 20F). Left BspP5 ornamented with setules and patches of small spinules (Fig. 20H–J); left Exp2P5 with long lateral seta (Fig. 21F); right CxP5 with distal process, ornamented with fine spinules (Fig. 20D, E); right BspP5 with smooth surface, with simple distal process (Fig. 20B); lateral spine of right Exp2P5 slightly curved at apex, inserted posterodistally on segment very close to base of claw (Figs 20A–E, 21E), reaching about to middle of terminal claw; terminal claw curved and twisted, with torsion in three planes. Leg 1 with distinctive spinulation on coxa, basipodite and both rami (Fig. 21G, H).

Figure 20. 

Argyrodiaptomus furcatus male. A P5; B–E Different views of P5R F Segment 1 of Enp of antenna 2 G Segment 20 of A1R; H–J Different views of P5L, showing details of ornamentation K Segments 12–16 of A1R.

Figure 21. 

Argyrodiaptomus furcatus male, SEM photographs. A A1R (500 µm) B A2R (200 µm) C Segments 10–15 and 20–22 of A1R (200 µm) D A1R (500 µm) E P5 (300 µm) F Distal segments of Exp2P5L (50 µm) G Right P1 (200 µm), anterior view H Distal segments of right P4 rami (50 µm), posterior view I Basis of right A2 showing spinules (20 µm).

Adult female, body length 1712 µm. Dorsal surface of Ped4 and Ped5 unornamented, lacking lines of spinules (Figs 22A, 23A). Incomplete suture present dorsally between Ped4 and Ped5; lateral wings slightly asymmetrical, left side larger than right (Fig. 23B); both wings with pair of sensillae, located at distal corner. GS asymmetrical, about twice as long as wide; slightly swollen anteriorly, more on left side than on right (Fig. 22A). P5 symmetrical, with small conical process at outer distal corner of CxP5 bearing short, triangular sensilla (Fig. 22B). BspP5 with short outer seta (Fig. 22C), measuring about 70–80% of external margin of EnpP5. EndP5 2-segmented, although suture only visible from certain angles (Figs 22C, 23C–E). ExpP5 3-segmented; lateral spine of Exp2P5 short, not exceeding length of external margin of Exp3P5; external seta of Exp3P5 about ¼ (25%) length of internal seta; internal seta about 2/3 length of terminal claw (Fig. 23E).

Figure 22. 

Argyrodiaptomus furcatus male. A Dorsal view of posterior pedigers and GS B P5 C Caudal view of left P5, with inset showing EnpP5.

Figure 23. 

Argyrodiaptomus furcatus female, SEM photographs. A Dorsal view (1000 µm) B Ped4, Ped5, and GS (500 µm) C P5 (300 µm) D P5 (150 µm) E EnpP5R and ExpP5R (100 µm).

The figured specimens were collected from the Iguaçu River at the reservoir of Foz do Areia (FARE-D) (Figure 24). This species was originally described from material collected in the state of São Paulo and, according to Wright (1927), occurs in Brazil (south and southeastern, and possibly also in the mid-west) and in Argentina. Santos-Silva (2008) and Previattelli et al. (2013) cited several records of A. furcatus from south and southeastern Brazil. Together these studies confirm the occurrence of this species mainly in reservoirs of southeastern and southern Brazil, and in northern Argentina. Along with other large species of this genus, this species can co-occur with A. azevedoi (in southeastern Brazil) and with Notodiaptomus spiniger (Brian, 1925) (in southern Brazil and northern Argentina). Argyrodiaptomus furcatus tends to be closer to N. spiniger in body size, whereas A. azevedoi is larger.

Figure 24. 

Geographical distribution of A. furcatus in de la Plata river basin.

Adult male, body length 1144 µm. Row of spinules present along posterior margins of Ped3 and Ped4 (Fig. 26A, B), Ped4 and Ped5 completely fused; A1R with well-developed spinous process on segments 15 and 16 (Figs 25A, 26C, E, F); segment 20 often with short curved distal process (Fig. 26C). Right Exp2P5 with two small nodules on surface (Fig. 25B); and bearing curved lateral spine inserted in middle of segment margin (Fig. 26G, H), and nearly half as long as terminal claw.

Figure 25. 

Notodiaptomus anisitsi male. A Segments 13–16 of A1R B P5.

Figure 26. 

Notodiaptomus anisitsi male, SEM photographs. A Ped3, Ped4, and Ped5 (100 µm) B Details of ornamentation on Ped3, Ped4 and Ped5 (100 µm) C Segments 10–22 of A1R (300 µm) D P5L (500 µm) E Segments 9–18 of A1R (200 µm) F A1R (500 µm) G Terminal somites of urosome and Exp2P5R (100 µm) H ExpP5R (100 µm).

Adult female, body length 1309 µm. Single row of spinules present along posterior margin of Ped3; irregular rows of spinules present, marking plane of posterior margin of Ped4; discrete transverse row of minute spinules present across middle of Ped5 (Fig. 27A). Lateral wings asymmetrical, similar in size but left wing located more anteriorly and right wing positioned and directed more posteriorly; both lateral wings with single sensilla at apex (Fig. 27A). GS nearly symmetrical, no more than 20% longer than wide; dilated anteriorly with left and right swellings of similar size, left sensilla on apex of swelling and aligned perpendicular to longitudinal axis of body; right sensilla directed postero-laterally. P5 symmetrical (Fig. 27B) with conical process at outer distal corner of CxP5 bearing strong triangular sensilla at apex. BspP5 with long outer seta, extending beyond middle of outer margin of Exp1P5. EnpP5 2-segmented, not reaching middle of inner margin of Exp1P5. ExpP5 3-segmented; lateral spine of Exp2P5 about as long as outer margin of Exp3P5; external seta of Exp3P5 less than 1/4 (25%) length of internal seta; internal seta almost reaching tip of terminal claw.

Figure 27. 

Notodiaptomus anisitsi female. A Dorsal view of Ped4 and Ped5, showing spinular ornamentation on dorsal surface, and GS B P5R.

The specimens illustrated were collected from the lower Paraná River (RPAR-L2). This species appears to be widely distributed in the south of the basin, from the Iguaçu River into more temperate conditions (Fig. 28).

Figure 28. 

Geographical distribution of N. anisitsi in de la Plata river basin.

Paggi (2001) provided good illustrations of this species and, in the same work, described a new species, N. dentatus Paggi, 2001, resembling and potentially confused with N. anisitsi. These two species deserve further investigation, as they may be part of a larger complex of species with very similar morphology.

Adult male, body length 1484 µm. Modified seta on segment 13 of A1R reaching distal end of segment 14 (Fig. 29A). Right BspP5 with longitudinal groove in surface, ornamented with small surface granulations (Fig. 29C). Right Exp2P5 with slightly outwardly curved lateral spine inserted on distal margin of segment, length about 1/3 of terminal claw; insertion of lateral spine separated from base of terminal claw by gap barely greater than basal width of spine (Fig. 29B, C).

Figure 29. 

Notodiaptomus carteri male. A Segments 13–16 of A1R B, C P5R, different views.

Adult female, body length 1770 µm. Ped4 and Ped5 separated by incomplete suture; process present on mid-dorsal surface of Ped4 (Fig. 30A, C); lateral wings slightly asymmetrical, with two pairs of sensillae on each side; internal sensilla of right side thin, setule-like; left sensilla slightly larger than right. GS asymmetrical, about 1.5 times longer than wide, swollen anteriorly (Fig. 30C), swelling on left side greater than that on right margin; left side swelling hemispherical, bearing single posterolaterally-directed sensilla; swelling on right side with projecting semi-circular lobe with posteriorly-directed sensilla. Right distal margin of GS longer than left, each side with rounded process at posterior end. P5 symmetrical (Fig. 30B) with small conical process at distal corner of Cx bearing short and triangular sensilla, about as long as wide. BspP5 with outer seta barely reaching middle of outer margin of Exp1P5. EnpP5 one-segmented, reaching 2/3 distance along inner margin of Exp1P5. ExpP5 3-segmented; lateral spine of Exp2P5 short, about as long as outer margin of Exp3P5; external seta of Exp3 about half length of internal seta; internal seta reaching middle of terminal claw.

Figure 30. 

Notodiaptomus carteri female. A Lateral view of dorsal process on prosome located near suture incomplete between Ped4 and Ped5 B P5R C Posterior pedigers and GS.

The illustrated specimens were collected from the lower Paraná River (RPAR-L2). The body length is slightly larger than the known range for males, 1315 to 1439 μm, given by Ringuelet and Martínez de Ferrato (1967). These authors published the first record from Argentina, near Santa Fe (equivalent to site RPAR-M3 in this study, Fig. 1), and they associated this species with the presence of floating aquatic macrophytes. The original description of this species (Lowndes 1934) was based on material from Paraguay, collected in flooded regions and wetlands, typically where there are macrophytes. In the present study the records of this species (Fig. 31) were about 500 km downstream from the locality sampled by Ringuelet and Martínez de Ferrato (1967). Santos-Silva (2008) provided records of this species from Paraguay, Argentina and southern Brazil, in the Patos Lagoon. Ringuelet and Martínez de Ferrato (1967) provided physical and chemical data for the water in the ponds where they found this species. Given the range of sites reported in this study, we infer that this species can occur in a wide range of habitat types.

Figure 31. 

Geographical distribution of N. carteri in de la Plata river basin.

Females of N. carteri can be readily distinguished from congeners by the asymmetrical swellings of the genital double-somite.

Adult male, body length 1008 µm. Ped4 lacking row of spinules along posterior margin. First segment of A1R unornamented (lacking typical spinule row) (Fig. 32B); modified seta of A1R on segment 13 forming strong process with bifid apex and reaching middle of segment 14 (Fig. 32C). Segment 11 of A1L with 2 setae (Fig. 32D). Right BspP5 slightly longer than wide with longitudinal groove ornamented with small surface granules (Fig. 32A); longitudinal groove also present on Exp2P5; lateral spine of Exp2P5 short and straight, length approximately 1/6 (16%) of length of terminal claw, inserted sub-terminally.

Figure 32. 

Notodiaptomus cearensis male. A P5 B Segments 1 and 2 of A1R C Segments 13–17 of A1R D Segments 12–10 of A1L.

Adult female, body length 1485 µm. Ped4 and Ped5 fused, without trace of suture; lateral wings symmetrical, both with two pairs of sensillae (Fig. 33A), one at distal tip, the other close to inner margin of wing. GS almost symmetrical, 1.3 times longer than wide; slightly dilated anteriorly, with swelling on right side slightly more marked than on left, both swellings with apical sensilla; left sensilla aligned perpendicular to longitudinal axis of body, right sensilla directed slightly anteriorly. P5 symmetrical (Fig. 33B), with short conical process at distal corner of Cx bearing triangular sensilla, longer than wide; BspP5 with long outer seta, almost reaching distal margin of Exp1P5; EnpP5 2-segmented, about as long as internal margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 similar in length to external margin of Exp3P5; external seta of Exp3 1/3 as long as internal seta; internal seta almost reaching apex of terminal claw.

Figure 33. 

Notodiaptomus cearensis female. A Dorsal view of posterior pedigers and GS B P5.

The illustrated specimens were collected from the Parnaíba River at Emborcação Reservoir (Fig. 34), where this species co-occurred with at least two other diaptomids: A. azevedoi and N. iheringi (Wright, 1935). This species has been widely reported from across the north and northeast of Brazil and in Venezuela. In de la Plata river basin, Tundisi and Matsumura-Tundisi (1994) found this species in Barra Bonita Reservoir. This species can be confused with N. iheringi, but differs in the setal formula of some segments of the A1, in the absence of a row of spinules on the first segment of A1R, and in having a smaller body than N. iheringi.

Figure 34. 

Geographical distribution of N. cearensis in de la Plata river basin.

Adult male, body length 1548 µm. Segment 1 of A1R with spinule row (Fig. 36F, G); segment 15 typically with well-developed spinous process reaching to end of segment (Figs 35A, 36A, B, E); process sometimes absent; segment 20 of A1R lacking distal projection. Enp1 of A2 ornamented with spinule row and single pore (Figs 35G, 36J). Right BspP5 with longitudinal fissure ornamented with surface granulations (Fig. 36H, I); Right Exp2P5 twice as long as wide (Figs 35B, 36C, D); lateral spine positioned close to outer distal angle of segment and directed posteriorly relative to longitudinal axis of body, length of lateral spine less than width of segment; terminal claw long and slightly curved (Fig. 35C–F), more slender than in N. cearensis.

Figure 35. 

Notodiaptomus conifer male. A Segments 13–16 of A1R B P5; C–F Different views of ExpP5R G First segment of Enp A2.

Figure 36. 

Notodiaptomus conifer male, SEM photographs. A Segments 13–16 of A1R (100 µm) B Segments 12–15 of A1R (100 µm) C Caudal view of P5 (100 µm) D Frontal view of P5 (100 µm) E Segments 13–17 of A1R (200 µm) F, G Segment 1 of A1R with spinule row arrowed (F = 50 µm; G = 20 µm) H P5L, and right Cx, Bsp and Exp1P5 (100 µm) I Detail of surface ornamentation of BspP5R (20 µm) J Segment 1 of Enp of A2 (50 µm).

Adult female, body length 1734 µm. Ped4 and Ped5 separated by complete suture; lateral wings slightly asymmetrical, each wing with sensilla at apex (Fig. 37A). GS asymmetrical, about 1.5 times longer than wide; slightly dilated anteriorly, with swelling on left side larger than on right, left swelling hemispherical with sensilla directed slightly posteriorly; right swelling more pronounced, sensilla located on dorsal surface, not on lateral margin; right lateral margin of GS with small projection about at 2/3 length and with small notch at posterior border (Fig. 37A). P5 symmetrical (Fig. 37B), with small expansion at outer distal corner of Cx, bearing large robust, triangular sensilla, approximately 1.5 times longer than wide. BspP5 with long outer seta, almost reaching distal margin of Exp1P5. EnpP5 with incomplete suture, similar in length to inner margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 similar in length to external margin of Exp3P5; external seta of Exp3P5 about 1/5 (20%) length of internal seta; internal seta attaining 3/4 length of terminal claw.

Figure 37. 

Notodiaptomus conifer female. A Dorsal view of posterior segments of prosome and GS B P5L.

The illustrated specimens were collected from the upper Tiete River, at the Barra Bonita Reservoir. In addition to the well-developed spinous process on segment 15 of A1R of the male, N. conifer can be distinguished from other congeners like N. iheringi and N. cearensis, by its larger body size. These species also differ in their relative lengths of the lateral spines on the right Exp3P5 of the male.

Earlier studies (Nogueira 2001, Nogueira et al. 2008; Matsumura-Tundisi and Tundisi 2003), which sampled several rivers in São Paulo State (Brazil) between 1970 and 2005 noted changes in the abundance of N. conifer. Matsumura-Tundisi and Tundisi (2003) suggested that such changes might be in response to variations in the ionic concentrations resulting from decreasing water quality and increasing conductivity over the surveyed period. Notodiaptomus conifer was found in the current study (based on samples taken in 2010) in only two reservoirs (JUR and BBON) (Fig. 38), and in both of these Matsumura-Tundisi and Tundisi (2003) had indicated that the species had disappeared. Studies on long time series (e.g. Polli and Simona 1992) have demonstrated cycles of 25 years for some diaptomid species, over which they dramatically decrease in population density but subsequently recover to become dominant again. It is necessary to sample extensively before putative disappearances can be confirmed.

Figure 38. 

Geographical distribution of N. conifer in de la Plata river basin.

Notodiaptomus conifer has been reported from Argentina to the northeast of Brazil, thus suggesting a widespread but scattered occurrence across South America.

Adult male, body length 1051 µm. Ped2, Ped3 and Ped4 ornamented with spinules near posterior margin (Fig. 40A). Ur3 to Ur5 lacking ventral spinulation (Fig. 40B). Segment 13 of A1R with strong spinous process (Fig. 39B) reaching distal margin of segment 14; segment 15 with short spinous process slightly larger than spinous process on segment 16 (Fig. 40C, G, H). Lateral spine of right Exp2P5 short, inserted on small lobe-like protuberance (Figs 39A, 40D, F); spine slightly curved towards terminal claw. Terminal claw smooth and relatively long (Fig. 40E) compared to other species, approximately twice length of internal margin of right Exp2P5.

Figure 39. 

Notodiaptomus coniferoides male. A P5 B Segments 13–16 of A1R.

Figure 40. 

Notodiaptomus coniferoides male, SEM photographs. A Pedigers 2–5 (200 µm) B Last 3 urosome somites, CR, and P5R (300 µm) C Segments 9–18 of A1R (200 µm) D Detail showing insertion of lateral spine on Exp2P5R (20 µm) E Exp2P5R (100 µm) F P5 (100 µm) G A1R (300 µm) H A1R from segment 7 to tip (200 µm).

Adult female, body length 1411 µm. Suture between Ped4 and Ped5 incomplete; conical dorsal process present on Ped4 (Figs 41A, 42A, B); lateral wings symmetrical, with two pairs of sensillae, larger pair on apex of each wing (Fig. 42B), each about twice as long as wide; inner pair of sensillae located dorsally near internal margin of each wing, each about as long as wide. GS asymmetrical, approximately 1.7/1.8 times longer than wide; anterior part slightly dilated, each anterior swelling with apical sensilla; left sensilla distinctly curved posteriorly, right sensilla aligned perpendicular to longitudinal body axis (Fig. 41A). P5 symmetrical with small conical process at outer distal corner of Cx bearing short, robust and triangular sensilla (Fig. 41B). BspP5 with external seta almost reaching middle of external margin of Exp1P5. EnpP5 2-segmented, almost reaching end of inner margin of Exp1P5; EnpP5 with 2 strong unequal apical spines. ExpP5 3-segmented; lateral spine of Exp2P5 almost as long as external margin of Exp3P5; internal seta on Exp3P5 about 3.5 times longer than external seta; internal seta reaching middle of terminal claw.

Figure 41. 

Notodiaptomus coniferoides female. A Posterior part of prosome and GS B P5.

Figure 42. 

Notodiaptomus coniferoides female, SEM photographs. A Posterior part of prosome, and GS (300 µm) B Posterior view of prosome and GS, showing detail of dorsal process on Ped4 and dorsal rows of spinules (200 µm).

The specimens illustrated here were collected in the upper Paraguay River. This is the only calanoid species that was found throughout the Paraguay basin (Fig. 43). Frutos et al. (2006) previously reported this species from along the Paraguay River. We did not find it in the basin of the Paraná River or the Uruguay River but it was previously observed in the middle section of the Paraná River by Dussart and Frutos (1985). Santos-Silva (2008) mentioned a record from the Itaipu Reservoir in the upper Paraná River basin, and other reports indicate its presence in the lower Paraná River, near the delta (e.g. Ringuelet 1958). The type locality of this species is in the Amazon (Wright 1927).

Figure 43. 

Geographical distribution of N. coniferoides in de la Plata river basin.

This species has a wide distribution in rivers and associated systems like marginal ponds, but it is not typically recorded in reservoirs. This species is easily distinguishable by the position of the lateral spine on a lobe on the coxa of P5 and by the length of spinous processes on segments 13 and 15 of the male A1R. Some studies have reported this species under the name Notodiaptomus coniferoide (sic.) (see Matsumura-Tundisi 1986), but the name presented in the original description by Wright (1927) is N. coniferoides.

Cicchino et al. (2001) described a new species from the Amazon region, which they named N. simmilimus, and its etymology alluded to its close resemblance with N. coniferoides. Comparison of the specimens described here with the observations made by previous authors revealed some distinctive features. However, we consider that the specimens from Venezuela identified as N. coniferoides by Dussart (1984) are in fact N. simmilimus, based on the differences in the proportions of BspP5 and the size of the modified seta on segment 13 of A1R. Dussart (1984) and Cicchino et al. (2001) did not refer to differences in the size of the modified seta on this segment, which tends to be smaller in N. simmilimus than in N. coniferoides. In the Amazonian specimens of N. coniferoides, the modified seta reaches the end of segment 14, according to the original description (Wright 1927), whereas in N. simmilimus it only extends to the middle of this segment.

We recommend a thorough comparative analysis of specimens of N. coniferoides found in the south of Brazil and in the lower Parana River. Comparison of our N. coniferoides with Amazonian specimens indicates that the material described in the present study was relatively smaller and we consider it is necessary to confirm the identity and status of N. coniferoides in de la Plata River Basin.

Adult male, body length 1046 µm. Posterior margin of Ped4 ornamented with more or less regular row of spinules (Fig. 44B). Small denticle present on outer margin of external caudal seta, near base (Fig. 44H). Modified seta on segment 13 of A1R well developed with minutely bifid apex, reaching middle of segment 14 (Fig. 44C); segment 20 of A1R variable, with or without falciform process. Right BspP5 1.8 times longer than wide, with longitudinal fissure ornamented with surface granulations. Surface of right Exp3P5 with 3-6 sclerotized processes (Fig. 44A, F, G); lateral spine of Exp2P5R short (Fig. 44A, D, E).

Figure 44. 

Notodiaptomus dentatus male. A P5 B Detail of spinular ornamentation on prosome 4 C Segments 12–16 of A1R D–G Different views of P5R H Caudal ramus showing tooth-like denticle on external seta.

Adult female, body length 1335 µm. Incomplete suture present between Ped4 and Ped5, with spinule row marking plane of fusion (Fig. 45A); row of spinules present dorsally along posterior margin of Ped4 (Fig. 45A); lateral wings of similar size but slightly asymmetrical; two sensillae, one large and one small, present on each wing; apical sensilla on left side located on small projection and with apex directed posteriorly; right sensilla located at apex of projection directed perpendicular to body axis. GS asymmetrical (Fig. 45A), approximately 1.9 times longer than wide. Anterior part slightly dilated, left swelling larger than right one; left side hemispherical, with strong sensilla at apex of swelling, about 1.5 times longer than wide; right side ornamented with sensilla at apex of triangular projection, sensilla about twice as long as wide; posterior to sensillate swelling, external margin sinuous in dorsal view, ending in well-developed lobe at posterior end of right side. P5 symmetrical (Fig. 45B), with small conical process at outer distal corner of CxP5 bearing triangular sensilla, about 1.4 times longer than wide. BspP5 with long outer seta long, reaching almost to end of outer margin of Exp1P5. EnpP5 one-segmented, length exceeding middle of inner margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 just reaching end of external margin of Exp3P5; external seta of Exp3P5 about 1/4 (25%) length of internal seta; internal seta extending almost to tip of terminal claw.

Figure 45. 

Notodiaptomus dentatus female. A Dorsal posterior part of prosome and GS B P5.

The illustrated specimens were collected from the middle stretch of the Paraná River (Fig. 46, RPAR-M3). The body length of the sampled specimens is slightly less than that reported by Paggi (2001) but falls within the known range for this species. Paggi (2001) highlighted two important characteristics of this species: 1) the presence of sclerotized processes on the surface of the right Exp2P5 of the male, and 2) the presence of a small tooth-like denticle on the outer margin of external caudal seta, near its base. This tooth-like process provides the basis for the etymology of the species.

Figure 46. 

Geographical distribution of N. dentatus in de la Plata river basin.

Adult male, body length 1123 µm. Dorsal suture between Ped4 and Ped5 incomplete (Fig. 48B); surface of Ped3, Ped4, and Ped5 ornamented postero-dorsally and laterally with fine covering of slender spinules (Fig. 48C–D). Lateral wings small, slightly asymmetrical, directed posteriorly; left side larger than right; both lateral wings with short, posteriorly-directed sensilla at distal corner, left sensilla better developed than right (Fig. 48B). GS slightly asymmetrical. Rostrum asymmetrical (Fig. 48H). Segment 1 of A1R ornamented with spinule row (Fig. 48E, F); modified seta on segment 13 reaching to end of segment 14 (Figs 47A, 48A, I). Bsp of A2 ornamented with spinules (Fig. 48G, J); Enp1 of A2 with spinule row (Fig. 47E). Cx and Bsp of P1 ornamented with long setules laterally (Fig. 49A). Right CxP5 with conical process bearing sensilla at apex (Figs 47H, J, 49G). Inner margin of right BspP5 with sclerotized knob, covered with tiny granulations (Figs 47C, D, 49C, E, F); right BspP5 with oblique fissure ornamented with small surface granulations (Fig. 47C); external seta of right BspP5 inserted subdistally, short, typically shorter than outer margin of Exp1P5. Right Exp1P5 bearing triangular process distally; right Exp2P5 with internal margin concave proximally, lateral spine slightly curved (Figs 47K, 49D) and inserted sub-terminally on external margin, less than 1/3 length of terminal claw (Fig. 47G–K). CxP5L with small conical process at outer distal corner bearing short apical sensilla; BspP5L with short external seta inserted distally; internal margin of BspP5L slightly concave, bearing two small sclerotized knobs proximally (Figs 47B–D, 49B, G), each ornamented with tiny granulations (Fig. 49C, E, F). EndP5 one-segmented, with row of spinules on inner distal margin (Fig. 47B, F). Exp2P5L with digitiform and sclerotized terminal process, lacking ornamentation.

Figure 47. 

Notodiaptomus henseni male. A Segments 12–16 of A1R B Left P5 C, D Different views of P5 E Segment 1 of Enp of A2 F P5L G–K Different views of P5R.

Figure 48. 

Notodiaptomus henseni male, SEM photographs. A Segments 13–16 of A1R (100 µm) B Ped4 and Ped5, and anterior part of urosome (100 µm) C Detail showing spinular ornamentation of Ped3 and Ped4 (100 µm) D Detail of spinules on Ped2-Ped4 (100 µm) E, F Segment 1 of A1R, showing spinular ornamentation (50 µm) G A2 (100 µm) H Rostrum and spinules on segment 1 of A1L (50 µm) I Segments 11–16 of A1R (100 µm) J Detail of Bsp of A2 (20 µm).

Figure 49. 

Notodiaptomus henseni male, SEM photographs. A P1, Details of spinular ornamentation on Cx and Bsp (50 µm) B Left and right P5 (150 µm) C Sclerotized processes on left and right BspP5 (10 µm) D P5 (100 µm) E, F Detail of sclerotized processes on left and right BspP5 (E = 20 µm; F = 10 µm) G P5 (200 µm).

Adult female, body length 1275 µm. Complete suture present between Ped4 and Ped5 (Fig. 50A); lateral surfaces of Ped3, Ped4 and Ped5 ornamented with covering of fine spinules (Fig. 51C); lateral wings more or less symmetrical (Fig. 51A); both wings with two sensillae, larger sensilla located at apex of wing and about 1.5 times longer than wide, smaller sensilla located near posterior margin of wing (Fig. 50A). GS asymmetrical, about 1.9 to 2 times longer than wide; slightly dilated anteriorly, with swelling of similar size on each side; each swelling with sensilla at apex; sensilla on right side of GS located at apex of hemispherical swelling; small lobe located at posterior end of right margin of GS (Figs 50A, 51A). Rostrum symmetrical (Fig. 51B). Fine setules present on segments 1 and 3 to 5 of A1 (Fig. 51E, F). P5 symmetrical (Fig. 50B) with small conical process at outer distal angle of CxP5, with short and strong sensilla, barely longer than wide. BspP5 with long external seta, extending beyond middle of external margin of Exp1P5. EnpP5 extending to middle of internal margin of Exp1P5, with incomplete suture (Fig. 51D). Exp 3-segmented; external seta of Exp2P5 exceeding length of external margin of Exp3P5 and similar in length to external seta of Exp3P5; external seta of Exp3P5 about 40% length of internal seta. Internal seta about 2/3 length of terminal claw.

Figure 50. 

Notodiaptomus henseni female. A Posterior part of prosome, GS and urosome B P5.

Figure 51. 

Notodiaptomus henseni female, SEM photographs. A Dorsal view of posterior part of prosome and GS (300 µm) B Ventral view of anterior end of cephalothorax, with rostrum and basal segments of antennule (150 µm) C Lateral view of posterior part of prosome, with arrows showing surface ornamentation of spinules, GS, urosome and CR (100 µm) D P5 (100 µm) E Dorsal view of segments 1 and 2 of left antennule, showing spinules (50 µm) F Dorsal view of segments 3–5 of left antennule, with some spinules (50 µm).

The specimens depicted here were collected in Furnas Reservoir on the Grande River (Fig. 52, FUR-U). Wright (1936) commented on the possible confusion between N. amazonicus (Wright, 1935) and N. henseni. However, comparisons between the specimens of N. henseni found in this work and N. amazonicus collected in Balbina Reservoir (Uatumã River, Amazonas) showed clear differences in the structure of P5 (Fig. 53), the dorsal spinular ornamentation of the prosomal somites, and in body length. In the present study, specimens of N. amazonicus similar to those obtained in the Amazon region were not found, but N. henseni was found to be widely distributed in the Upper Paraná River. There are significant differences in size range between N. henseni and N. amazonicus (Fig. 54). Notodiaptomus amazonicus males had a body length of 1608 µm and a body width of 397 µm, both significantly larger than N. henseni, whose body length does not exceed 1300 µm. It is possible that some records of N. amazonicus from de la Plata basin are erroneous, reflecting the taxonomic confusion between this species and N. henseni. For example, Ringuelet and Martinez de Ferrato (1967) reported a body length of about 1270 µm for a diaptomid identified as N. amazonicus in Argentina. However, this length is much less than would be expected for this species and falls within the typical size range of N. henseni.

Figure 52. 

Geographical distribution of N. henseni in de la Plata river basin.

Figure 53. 

Notodiaptomus amazonicus male. P5. Specimen sampled in the Balbina Reservoir, Uatumã River (Central Amazonia), in the State of Amazonas, Brazil.

Figure 54. 

Light micrograph comparing males of N. henseni (on left) – specimen from the Grande River (FUR-D), and N. amazonicus (on right) – specimen from Uatumã River, State of Amazonas, Brazil.

In addition, Ringuelet and Martinez de Ferrato (1967) mentioned that their specimens of N. amazonicus that carried a process on segment 20 of the male A1R were larger (about 1375 µm), a condition which is closer to the expected size of N. amazonicus from the Amazon region, although still relatively small. More comparisons are needed between specimens of N. amazonicus from the Amazon basin and those reported by other researchers from de la Plata River Basin.

Recently, Matsumura-Tundisi et al. (2010) described a new species, Notodiaptomus oliveirai Matsumura-Tundisi, Espindola, Tundisi, Souza-Soares & Degani, 2010, which shows a close similarity to N. henseni, and stated that many records of N. henseni from the state of São Paulo (Brazil) would represent records of N. oliveirai. However, their description is supported by illustrations lacking many important details (e.g. description of A1 formula, dorsal spinules) and the diagnostic difference between these two species as stated by these authors was based only on the curvature of the outer margin of the second segment of the exopod of right P5 (Exp2P5R). We consider this evidence insufficient to justify the establishment of a new species. The form of the P5 appears to vary according to the angle of observation (e.g. Fig. 47G to 47K), and this can be misleading. The degree of curvature alone does not provide adequate evidence upon which to base the establishment of a new species. The typical sclerotized processes on internal margins of left and right BspP5 of N. henseni are visible in the photograph of N. oliveirai included by Matsumura-Tundisi et al. (2010) and their presence provides further evidence pointing to the synonymy of this nominal species. We formally propose the recognition of N. oliveirai as a junior subjective synonym of N. henseni.

Adult male, body length 922 µm. Posterior margin of Ped3 ornamented with rows of spinules; Ped4 and Ped5 ornamented with spinule rows along posterior margins and on lateral surfaces (Fig. 56B–F). Rostral filaments asymmetrical (Fig. 56A). Single row of spinules present on first segment of A1R (Figs 55D, 56G, H); modified seta on segment 13 of A1R strong, with minutely bifid apex, reaching beyond level of insertion of proximal seta on segment 14 (Fig. 55A); spinous process of segment 15 longer than spinous process of segment 16) (Fig. 57A, B). Enp1 of A2 ornamented with pore and spinule row (Figs 55G, 56I). Cx of P1 with setules on outer surface (Fig. 57E). Right and left internal margins of P5 without sclerotized processes (Figs 55B, C, 57G). Right BspP5 with irregular oblique fissure on middle of surface; distal part of fissure ornamented with small surface granulations; external seta inserted distally on lateral margin. Lateral spine on right Exp2P5 inserted in distal third of external margin, length about 1/6 (16%) of length of terminal claw (Figs 55E, F, 57C, D, F, G).

Figure 55. 

Notodiaptomus iheringi male. A Segments 13–15 of A1R B, C Different views of P5 D Segments 1 and 2 of A1R E, F Different views of terminal segments of ExpP5 G Segment 1 of Enp of A2.

Figure 56. 

Notodiaptomus iheringi male, SEM photographs. A Rostrum (20 µm) B Ped4 and Ped5, lateral view (50 µm) C Ped3, Ped4, Ped5, lateral view (100 µm) D Detail of spinular ornamentation adjacent to sensilla on Ped5 (50 µm) E Ped4 and Ped5 (100 µm) F Ped3 and Ped4 (20 µm) G, H Segment 1 of A1R, showing row of spinules (50 µm) I Segment 1 of Enp of A2 (50 µm).

Figure 57. 

Notodiaptomus iheringi male, SEM photographs. A Segments 12–16 of A1R (100 µm) B Segments 13–16 of A1R C, D P5R (C = 100 µm; D = 200 µm) E Detail of spinules on Cx and BspP1 (20 µm) F P5R (200 µm) G P5 (100 µm).

Adult female, body length 1093 µm. Incomplete suture present between Ped4 and Ped5 with plane of fusion marked by transverse row of strong spinules, with double row in middle section of dorsal surface (Figs 58A, 59D); lateral surfaces of posterior prosomal somites ornamented with spinules (Fig. 59F). Lateral wings bearing two unequal sensillae; large sensilla located at apex about 1.5 times longer than wide. GS asymmetrical, about 1.3 to 1.4 times longer than wide; dilated anteriorly, swellings of similar size; left swelling hemispherical; both swellings bearing sensilla approximately 2.5 times longer than wide, right sensilla inserted on dorso-lateral surface and not on apex of swelling (Figs 58A, 59A). P5 symmetrical (Fig. 58B) with small conical process at outer distal corner of Cx bearing short, robust triangular sensilla, about 1.1 times longer than wide. BspP5 with long external seta, extending beyond distal end of external margin of Exp1P5 (Fig. 58B). EnpP5 one-segmented (Fig. 59C, G), about 3/4 length of internal margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 not reaching end of external margin of Exp3P5; external seta of Exp3P5 approximately 3.5 times shorter than internal seta; internal seta reaching just beyond middle of terminal claw (Fig. 59D).

Figure 58. 

Notodiaptomus iheringi female. A Dorsal posterior part of prosome, GS and Ur2 B P5.

Figure 59. 

Notodiaptomus iheringi female, SEM photographs. A Dorsal posterior pedigers and GS (500 µm) B Male, ventral view (500 µm) C P5L (100 µm) D Posterior pedigers (100 µm) E Exp3P5 and terminal claw (20 µm) F Ventral view of posterior part of prosome (100 µm) G P5L (100 µm).

Our specimens were taken in the Grande River at Furnas Reservoir. In the present study this species was found in southeastern and southern Brazil and in the upper part of the Paraná River basin, with its southerly distribution boundary represented by the Iguaçu River (Fig. 60). Other studies (Santos-Silva 2008) indicate a widespread distribution in Brazil, and the type locality is in Paraiba State in northeastern Brazil, but it also occurs in some parts of northern Argentina. This species can be confused with its congeners N. cearensis and N. isabelae (Wright, 1936), but details of the male A1R and P5 are useful to distinguish N. iheringi from these other two species. This species also resembles N. conifer in possessing a small lateral spine on the P5, but N. conifer has a well-developed spinous process on segment 15 of A1R (Fig. 35A), which is much larger than that of N. iheringi (Fig. 55A). In the present study this species occurred in a variety of habitats with different trophic states, from oligotrophic, such as the Emborcação and Furnas reservoirs, to the eutrophic Barra Bonita and Foz do Areia reservoirs. Its presence or absence, therefore, is not indicative of trophic status and this species is not suitable for biomonitoring purposes.

Figure 60. 

Geographical distribution of N. iheringi in de la Plata river basin.

Adult male, body length 1029 µm. Rows of spinules present dorsally along posterior margins of Ped3 and Ped4 (Fig. 62A), and dorsal surfaces of Ur3 and Ur4 extensively ornamented with patches of small spinules (Fig. 62E, F). Caudal setae modified; each seta with strong plumose setules bilaterally and rounded apex (Fig. 61B, C). Modified seta of segment 13 of A1R strong, with bifid apex and not extending beyond distal margin of segment 14; spiniform process on segment 15 larger than on segment 16 (Figs 61A, 62D). Enp1 of A2 ornamented with pore and spinule row (Fig. 61E). Right BspP5 with internal and outer margins smooth (Fig. 62G). Right Exp1P5 longer than wide; right Exp2P5 cylindrical, internal margin with sclerotized process near middle (Figs 61D, 62B); lateral spine of Exp2P5 inserted subterminally, slightly curved, short, less than 1/3 length of terminal claw (Fig. 62C).

Figure 61. 

Notodiaptomus incompositus male. A Segments 13–16 of A1R B Caudal seta showing reticulate form C Dorsal view of CR D P5 E First segment of Enp of antenna.

Figure 62. 

Notodiaptomus incompositus male, SEM photographs. A Dorsal view of Ped3, Ped4, Ped5 and GS (100 µm), showing detail of dorsal rows of spinules B, C P5 (100 µm) D Segments 10–15 of A1R (100 µm) E Dorsal view of Ur4 (50 µm) F Dorsal view of Ur3 (20 µm) G P5L, and Cx and Bsp of P5R (100 µm).

Adult female, body length 1310 µm. Complete suture present between Ped4 and Ped5; transverse row of short spinules present along posterior margin of Ped4 (Fig. 63A); row of long setules, present dorsally on Ped5 (Fig. 64B); lateral wings asymmetrical (Fig. 64A, B), left wing narrower than right, each with two unequal sensillae, large sensilla at apex of wing. Sensilla about 1.5 times longer than wide. GS asymmetrical, approximately 1.5 times longer than wide: slightly dilated anteriorly, with swelling on right side larger than left; sensilla present at apex of each swelling, slightly on dorso-lateral surface on right side (Fig. 63A). P5 symmetrical (Figs 63B, 64C) with small conical process at outer distal corner of CxP5 bearing long blunt sensilla, approximately 2.6 times longer than wide. BspP5 with long external seta, equal in length to external margin of Exp1P5. EnpP5 approximately 3/4 of length of internal margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 as long as external margin of Exp3P5; internal seta of Exp3 about 2.3 times longer than external seta; internal seta reaching almost to middle of terminal claw (Fig. 64C).

Figure 63. 

Notodiaptomus incompositus female. A Posterior part of prosome and GS, showing details of dorsal spinule row B P5.

Figure 64. 

Notodiaptomus incompositus female, SEM photographs. A Dorsal view (100 µm) B Posterior pedigers and GS (50 µm) C P5 (100 µm).

This species was collected in the Machadinho Reservoir (MAC-U) on the Uruguay River and it can be easily identified by the unusual form of the caudal setae. It is distributed across the southern part of de la Plata river basin, including southern Brazil, south of the Iguaçu River (Fig. 65), and it also occurs widely in Argentina and Uruguay. In the present study, N. incompositus was among the dominant species and it tended to occur abundantly in reservoirs and river stretches irrespective of their trophic status (eutrophic, mesotrophic, and oligotrophic), as observed for N. henseni. In general, N. henseni was the dominant species in the northern part of de la Plata river basin, while N. incompositus was dominant in the southern sector.

Figure 65. 

Geographical distribution of N. incompositus in de la Plata river basin.

Adult male, body length 919 µm. Transverse row of strong spinules present along posterior margin of Ped4 (Fig. 66B, C). Modified seta on segment 13 of A1R extending beyond middle of segment 14, but not reaching end of segment; spinous process present on segments 15 and 16 of A1R (Fig. 66G). Two small expansions present proximally on internal margin of right BspP5 (arrowed in Fig. 66A); right Exp1P5 with wide distal expansion on margin (Fig. 66D, F); right Exp2P5 broad, with width about ¾ length (Fig. 66A, E); lateral spine short, inserted distally, close to insertion of terminal claw.

Figure 66. 

Notodiaptomus isabelae male. A P5 B Ornamentation of spinules on Ped4 C Lateral view of Ped3, Ped4 and Ped5, showing details of the spinule rows D–F Different views of P5R G Segments 12–16 of A1R.

Adult female, body length 1056 µm. Complete suture present between Ped4 and Ped5, ornamented with row of strong spinules dorsally (Fig. 67A); lateral wings asymmetrical, left wing smaller and located anterior to right wing; two pairs of sensillae present on each wing, large sensilla on left positioned on small dorsal projection; large sensilla on right positioned at apex of wing. GS asymmetrical, approximately 2.5 times longer than wide; anterior part slightly dilated, with swelling on right side larger than that on left; left swelling rounded with strong sensilla at apex, approximately 1.5 times long than wide; anterior swelling on right side with strong sensilla at apex, approximately twice as long as wide; anterior swelling extending back along two thirds of lateral margin to acute indentation; margin straight posterior to indentation (Fig. 67A). P5 symmetrical (Fig. 67B) with small conical process at outer distal corner of CxP5, bearing sensilla with rounded apex, barely longer than wide. BspP5 with external seta reaching middle of external margin of Exp1P5. EnpP5 one-segmented, about as long as inner margin of Exp1P5. ExpP5 three-segmented; lateral spine of Exp2P5 almost reaching distal tip of external margin of Exp3P5; external seta of Exp3P5 about one third length of internal seta; internal seta about two thirds length of terminal claw.

Figure 67. 

Notodiaptomus isabelae female. A Dorsal posterior pedigers and GS B P5.

The specimens were collected in the middle section of the Paraná River at Yaciretá Reservoir (Fig. 68, YACI-D). The type locality of this species is in the state of Pernambuco (northeastern Brazil) but this species is distributed across much of Brazil and Argentina, with its southernmost boundary in the middle region of the Paraná River. It does not seem to occur in the Iguaçu and Uruguay rivers, and the low winter temperatures in this region may be a factor limiting its distribution. Dussart and Frutos (1986) recorded this species in the middle section of the Paraná River.

Figure 68. 

Geographical distribution of N. isabelae in de la Plata river basin.

This species can be easily distinguished from its congeners by the proximal processes on the internal margin of the male right BspP5 and by the shape of the wings and GS of females. A comparison with the description by Paggi (1976) revealed minor differences in the shape of segment 20 of the male A1R. No falciform process was found on this segment in our specimens, but this absence can occur in some populations, and a similar range of variability of this process has been noted for other species (Ringuelet and Martínez de Ferrato 1967, Paggi 1976).

Adult male, body length 967 µm. Dorsal and lateral surfaces of Ped3, Ped4 and Ped5 ornamented with scattered setules (Fig. 70A). Segment 1 of A1R with setule row (Fig. 70H); segment 13 with modified seta reaching beyond middle of segment 14; segments 15 and 16 each with small spinous processes (Figs 69I, 70D); distal margin of segment 20 of A1R terminating in small bifid process (Fig. 69J, K). Tips of rami of P4 ornamented with minute spinule combs (Fig. 70C, G). Left and right CxP5 each with conical process bearing sensilla at apex (Figs 69A, G, 70B, E). BspP5L with smooth inner surface, lacking spinulation or processes (Figs 69A, 70E). Right BspP5 with smooth inner surface, lacking spinulation or processes (Fig. 69A), outer seta short, less than half length of external margin Exp1P5; lateral spine on right Exp2P5 inserted close to insertion of terminal claw, strong and slightly outward curved, approximately four times longer than wide (Figs 69B–H, 70F); terminal claw with main curvature in proximal 1/3.

Figure 69. 

Notodiaptomus santafesinus male. A P5 B Right Exp2P5; C–H Different views of P5R I Segments 13–16 of A1R J, K Different views of segment 20 of A1R.

Figure 70. 

Notodiaptomus santafesinus male, SEM photographs. A Dorsal view of right side of Ped3, Ped4 and Ped5 (100 µm) B Right P5 (300 µm) C Terminal segments of EnpP4 and ExpP4 (100 µm) D Segments 13–17 of A1R (200 µm) E P5L (100 µm) F Detail of Exp2P5R (50 µm) G Detail of ornamentation of spinules of EnpP4 and ExpP4 (50 µm) H Segments 1 and 2 of A1R (100 µm).

Adult female, body length 1271 µm. Incomplete suture present between Ped4 and Ped5; lacking rows of spinules on posterior margin of pedigers (Fig. 71A). Dorsal process present on midline of Ped4 (Fig. 71A, C); lateral wings slightly asymmetrical; both projections with pair of sensillae, one large and one small. GS slightly asymmetrical, about 1.8 to 1.9 times longer than wide; anterior part slightly dilated, with sensilla at apex of each swelling; left sensilla positioned slightly anterior to right; left sensilla directed slightly posteriorly, right sensilla directed slightly anteriorly. P5 symmetrical (Figs 71D, 72A) with small conical process at outer distal corner of CxP5, bearing sensilla approximately 1.5 times longer than wide; BspP5 with external seta of medium length, not exceeding length of internal margin of Exp3P5. EnpP5 unsegmented, reaching middle of inner margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 shorter than external margin of Exp3; external seta of Exp3 about half length of internal seta; internal seta almost reaching middle of terminal claw (Fig. 72B).

Figure 71. 

Notodiaptomus santafesinus female. A Dorsal posterior segments of prosome, with dorsal process, and GS B Lateral view of posterior margin of prosome, GS and urosome C Lateral view of prosome, showing dorsal process D P5.

Figure 72. 

Notodiaptomus santafesinus female, SEM photographs. A P5 (100 µm) B Detail of Exp3P5 and terminal claw (50 µm).

The specimens examined were collected in the lower stretch of the Paraguay River (RPAG–B). This species is found in Argentina in the middle and lower stretches of the Paraná River and it can be considered to be a common species in the zooplankton community of this region (Fig. 73). However, Ringuelet and Martínez de Ferrato (1967) found that this species was uncommon during the period of their study, occurring in lotic or adjacent systems only between February and April. It was not found in reservoirs. This species can be readily distinguished from its congeners because of the position of the robust lateral spine on the right Exp2P5, close to the insertion of the terminal claw.

Figure 73. 

Geographical distribution of N. santafesinus in de la Plata river basin.

Adult male, body length 1466 µm. Patches of spinules present dorsally and laterally along suture between Ped3 and Ped4 (Figs 74B, C, 75A), and on the surface of Ur3 and Ur4 (Fig. 75E). Modified seta well developed on segment 13 (Fig. 74D, Q) and spinous process well developed on segment 15 of A1R (Figs 74Q, 75H); segment 20 of A1R typically produced into distal falciform process, longer than wide (Figs 74J, 75D, F), but process sometimes absent (see Dussart and Frutos 1985). End1 of A2 ornamented with spinule row, lacking pore (Fig. 74I). Rounded mammiform process present on internal margin of right BspP5 (Figs 74A, P, 75B, G). Left CxP5 1.5 times longer than wide; BspP5L about 1.2 longer than wide (Fig. 74K–M). Lateral spine of right Exp2P5 straight, almost as long as segment, inserted close to origin of terminal claw; terminal claw long, approximately 3 times as long as lateral spine (Figs 74F–H, N, O, R, 75C).

Figure 74. 

Notodiaptomus spiniger male. A Dorsal P5 B Ped3 and Ped4, showing details of spinular ornamentation C Details of spinules on corner of Ped4 D Spinous process of segment 13 of A1R E–G P5R H First segment of Enp of antenna 2 I Segment 20 of A1R J–L Different views of P5L M, N Different views of P5R O Detail of mammiform process on internal margin of right BspP5 P Segments 13–16 of A1R Q P5R.

Figure 75. 

Notodiaptomus spiniger male, SEM photographs. A Dorsal prosome and urosome, showing details of spinular ornamentation (200 µm) B, C P5 (150 µm) D A1R (120 µm) E Dorsal urosome somites 3 and 4, showing details spinular ornamentation (100 µm) F Segments 19 and 20 of A1R (100 µm) G Mammiform process on internal margin of BspP5R (20 µm) H Spinous process on segment 13 of A1R, and segments 14–17 (200 µm).

Adult female, body length 1688 µm. Complete suture present between Ped4 and Ped5; with several irregular rows of spinules present dorsally along posterior margin of Ped4 (Figs 76A, 77A–C); lateral wings slightly asymmetrical, left wing larger than right; both wings bearing pair of sensillae, one large and one small; large sensilla on left side located on hemispherical projection, right sensilla located on apex of wing (Fig. 77C). GS asymmetrical, about 1.5 times longer than wide; anterior part slightly dilated, with swelling on left side larger than on right, sensilla present on apex of each, both about twice as long as wide; sensilla on right side directed perpendicular to long axis of body (Fig. 76A). Right margin of GS longer than left. Cx of P1 with spinules on antero-lateral surface (Fig. 77G). P5 symmetrical (Fig. 76B) with small conical process at distal corner of CxP5, bearing triangular sensilla approximately 1.8 times longer than wide. BspP5 with outer seta of medium length, reaching middle of external margin of Exp1P5 (Fig. 77D). EnpP5 one-segmented, slightly longer than internal margin of Exp1P5. Exp 3-segmented; lateral spine of Exp2P5 long, reaching middle of external seta of Exp3P5 (Fig. 77E); internal seta of Exp3P5 about 3.5 times longer than external seta of Exp3P5; internal seta of Exp3P5 extending beyond middle of terminal claw.

Figure 76. 

Notodiaptomus spiniger female. A Dorsal posterior pedigers, showing details of spinular ornamentation on dorsal surface, and GS B P5.

Figure 77. 

Notodiaptomus spiniger female, SEM photographs. A Dorsal view of adult (500 µm) B Posterior pedigers, showing details of spinule rows, and GS (150 µm) C Dorsal view of posterior pedigers showing details of spinule rows, and GS (150 µm) D P5L (50 µm) E P5L (100 µm) F ExpP5 (50 µm) G Left P1, showing details of rows of spinules on Cx (100 µm).

The illustrated specimens were caught in the upper reaches of the Uruguay River, in the Machadinho Reservoir. The northernmost boundary of its distribution may lie in the northern sector of Paraná State (Brazil), its northernmost record is from the floodplain of the upper Paraná River (Fig. 78).

Figure 78. 

Geographical distribution of N. spiniger in de la Plata river basin.

This species has been the subject of much taxonomic confusion. Ringuelet and Martínez de Ferrato (1967) argued that misinterpretation of the intraspecific variability of the spinous processes on segment 15 and of the falciform process on segment 20 of the male A1R is responsible for the establishment of “Diaptomus” toldti Pesta, 1927, a junior subjective synonym of N. spiniger. They added that individuals with well-developed spinous processes typically had a larger body size. Brehm (1933) included this species in the genus Argyrodiaptomus, but Kiefer (1936) doubted its inclusion in the genus because of its possession of a mammiform process on the internal margin of the right BspP5 and thus suggested an affinity with Notodiaptomus. Some subsequent authors (e.g. Ringuelet and Martínez de Ferrato 1967) have placed this species in “Diaptomus” as D. spiniger, while Dussart and Defaye (2002) treated it as incertae sedis within Argyrodiaptomus.

There are two other synonyms: “Diaptomus” birabeni Brehm, 1957 and Notodiaptomus orellanai Dussart, 1979 as proposed by Paggi in his MS Thesis in 1994. In each case the new species was established on the basis of morphological characters (Brehm 1957, Dussart 1979), but both synonymies are now widely accepted.

Further study of this species is necessary, including study of museum collections, in order to verify these synonymies and assess the evidence supporting the placement of this species in the genus Notodiaptomus, in part because of the presence of a mammiform process on the internal margin of the right BspP5, a character which conflicts with the current diagnosis of the genus.

Adult male, body length 1088 µm. Small chitinous knob present distally on internal margin of left CR, other small chitinous processes present on right CR (Fig. 80B, E). Modified setae on segments 10, 11 and 13 of A1R large (Figs 79C, 80A); segment 14 lacking spinous process; spinous processes on segments 15 and 16 well developed; segment 20 of A1R bearing dentate hyaline membrane (Fig. 79B). Right CxP5 with small chitinous knob on surface in middle of segment (Fig. 79A). Right BspP5 bearing three rounded chitinous projections on internal margin. Right EnpP5 2-segmented (Figs 79A, 80D). Right Exp1P5 with semi-circular chitinous knob on distal margin, visible in anterior view; right Exp2P5 with lateral spine inserted proximally (Figs 79A, 80C), about 6 to 7 times longer than wide. Terminal claw of right Exp2P5 about 2.3 times longer than lateral spine. CxP5L with distal outer projection bearing sensilla about 3 times longer than wide (Fig. 79A); well-developed outer seta present on BspP5L.

Figure 79. 

Odontodiaptomus thomseni male. A P5 in frontal view B Segment 20 of A1R C Segments 10–16 of A1R.

Figure 80. 

Odontodiaptomus thomseni male, SEM photographs. A Dorsal view of segments 11–16 of A1R (500 µm) B Detail of small chitinous knob on internal margin of left CR (20 µm) C P3, P4 and right P5 (caudal view), showing detail of EnpP5, lateral spine of P5 (200 µm) and were the semi-circular knob in inserted in Exp2P5 in frontal view D Right EnpP5 (2 µm) E Detail of chitinous knob on internal margin of CR (2 µm) F Detail of terminal claw (20 µm).

Adult female, body length 1245 µm. Incomplete suture present between Ped4 and Ped5; surface of Ped4 and Ped5 smooth, lacking rows of spinules dorsally along posterior margin (Fig. 81A); lateral wings slightly asymmetrical, similar in size; left sensilla directed posteriorly, right sensilla perpendicular to body axis (Fig. 82A). GS asymmetrical, about 1.6 times longer than wide; anterior part slightly dilated, with swelling on right side anterior to that on left; right side margin with large rounded process at posterior end (Fig. 81A). Ur2 with small chitinous process on outer margin on left side (Fig. 82B). P5 symmetrical (Fig. 81B) with small conical process at outer distal corner of CxP5, bearing short robust sensilla; BspP5 with short outer seta, about as long as EnpP5. EnpP5 one-segmented. ExpP5 3-segmented; lateral spine of Exp2P5 exceeding external margin of Exp3P5; external seta of Exp3P5 nearly 2/3 length of internal seta; internal seta robust, only about 1/5 length of terminal claw (Fig. 82C, D).

Figure 81. 

Odontodiaptomus thomseni female. A Posterior pedigers and GS B P5.

Figure 82. 

Odontodiaptomus thomseni female, SEM photographs. A Ventral view of posterior pedigers, GS, urosome and base of CR (100 µm) B Detail of chitinous knobs on left external margin of last somite of urosome (10 µm) C P5 (100 µm) D Exp3P5 and terminal claw (25 µm).

The specimens were collected in the low stretch of the Uruguay River at Salto Grande Reservoir (Fig. 83, SGRA-D). Only three individuals were found and a full re-description was published by Perbiche-Neves et al. (2012). This species is on the red list of endangered species (IUCN–Red List of Threatened Species, 2010–Reid 1996), due to lack of recent records. The only previous confirmed record of this species was its original description (Brehm 1933). There is a subsequent record of this species from pools in Venezuela, but it is doubtful and requires confirmation (Perbiche-Neves et al. 2012). Ringuelet (1958) did not find this species in his work on Argentinian copepods, nor did Paggi and José de Paggi (1990). This was only the second confirmed record of this rare species in 77 years.

Figure 83. 

Geographical distribution of O. thomseni in de la Plata river basin.

The genus Odontodiaptomus comprises three species (equivalent to the thomseni group of Wright 1936), and there is a great interest in the genus because of its apparent isolation from other Neotropical Diaptomidae (Santos-Silva 2008). A second species of this genus, Odontodiaptomus paulistanus (Wright, 1936) is relatively common in Brazil, but was not found in the present study. The third species, O. michaelseni (Mrázek, 1901), was not found in our study.

Adult male, body length 923 µm. Ur4 with triangular-shaped dorsal process ornamented with small granulations at left distal corner (Figs 84F, 85F, G), length similar to width of Ur4. CR asymmetrical, left ramus larger than right, internal seta of CR with narrow section close to base (Fig. 84F). Segment 11 of A1R with modified seta on anterior margin longer than modified seta on segment 13; spinous processes present on segments 15 and 16 (Figs 84C, 85A, C); segment 20 with small, curved, distal process (Fig. 85E). Two rows of spinules present on surface of Enp1 of A2 (Fig. 84D). Small mammiform process present proximally on internal margin of left and right BspP5 (Fig. 84A); lateral spine on right Exp2P5 strong, inserted proximally, curved in midsection, about 2/3 length of terminal claw (Figs 84A, E, 85D); base of terminal claw thick, almost same width as thinnest part of Exp2P5. Right EnpP5 tapering distally, ornamented with spinules subapically (Figs 84A, 85B). Lateral seta of CxP5L as long as width of segment; BspP5L as wide as long (Fig. 84B).

Figure 84. 

“Diaptomus” curvatus male. A P5 B Left P5 C Segments 10–16 of A1R D First segment of Enp of antenna 2 E Right P5 F Urosome somites 2–4 and CR, showing dorsal process on Ur4 (arrowed).

Figure 85. 

“Diaptomus” curvatus male, SEM photographs. A A1R (150 µm) B Detail of endopod of P5R (25 µm) C Segments 11–14 of A1R (50 µm) D P5 (200 µm) E Segment 20 of A1R (50 µm) F End of urosome and CR, showing detail of dorsal process (50 µm) G Detail of dorsal process on Ur4 (20 µm) H Right P5 (100 µm).

Adult female, body length 1120 µm. Incomplete suture present between Ped4 and Ped5; dorsal surface smooth, without spinules (Fig. 86A); lateral wings asymmetrical, left wing larger than right. GS slender, asymmetrical, about 1.6 times longer than wide; anterior part slightly dilated, with swelling on left side larger than right. P5 symmetrical (Fig. 86B) with small conical process at distal corner of CxP5, bearing short, triangular sensilla. BspP5 with long external seta, extending beyond base of terminal claw. EnpP5 one-segmented. ExpP5 3-segmented; lateral spine of Exp2 longer than external margin of Exp3P5; external seta of Exp3P5 about two thirds length of internal seta; internal seta reaching mid-length of terminal claw.

Figure 86. 

“Diaptomus” curvatus female. A Posterior pedigers and GS B P5.

Several individuals of this species were found in the Yaciretá Reservoir (Fig. 87, YACI-B) in the middle Paraná River. This species had been found by S. M. Frutos (pers. comm.) in Yaciretá Reservoir, and J. C. Paggi (pers. comm.) found three males in the middle section of the Paraná River in 1971 and in 1993. This species is distinct from all other Diaptomidae found in South America, especially with regard to the P5 and the dorsal process on the Ur4. A preliminary phylogenetic analysis based on morphological characters was inconclusive with regard to which genus this species should be attributed to, thus suggesting the possibility that it represents a new genus. However, Perbiche-Neves et al. (2013) decided to maintain the status as “Diaptomus” sensu lato until a comprehensive phylogenetic analysis of Neotropical diaptomids could be completed.

Figure 87. 

Geographical distribution of D. curvatus in de la Plata river basin.

Adult male, body length 1292 µm. Irregular row of spinules present dorsally and laterally along posterior margin of Ped4 (Fig. 88A). Modified seta on segments 11 and 13 well developed, that on segment 13 longest, extending to end of segment 14 (Fig. 89G, H); spinous process well developed on segments 15 and 16 of A1R; spinous process on segment 15 longer than that on segment 16; falciform process on segment 20 of A1R in all specimens analysed (N=16), reaching beyond middle of apical segment, proximal surface of process rugose (Fig. 88G, 89I, J). Right CxP5 with well-developed distal process bearing short sensilla (Fig. 89E). Right Exp1P5 short, about 1.5 times wide than long; right Exp2P5 flattened, subtriangular in shape (Fig. 89C–D), wider than long, with swollen outer margin proximal to insertion of outer seta (Fig. 89A, C, 88B); outer seta slightly curved (Fig. 88B, 89C). Terminal claw strongly curved near tip (Figs 88D–F, H, 89F). Strong seta present on distal margin of CxP5L.

Figure 88. 

“Diaptomus” frutosae male. A Ped4 and Ped5, showing details of spinule rows B P5 C Segments 11–16 of A1R D–F Different views of P5 G Segment 20 of A1R, showing falciform process H P5.

Figure 89. 

“Diaptomus” frutosae male, SEM photographs. A P5R, caudal view (300 µm) B P5L (50 µm) C Last segment of ExpP5L (200 µm) D P5 (100 µm) E Cx and Bsp of right P5 (100 µm) F Right P5, lateral view (200 µm) G Segments 12–14 of A1R (50 µm) H Segments 13 and 14, showing details of spinous process on segment 13 (50 µm) I Segment 20 of A1R (20 µm) J A1R (200 µm).

Adult female, body length 1346 µm. Incomplete suture present between Ped4 and Ped5; rows of strong spinules marking position of posterior margin of Ped4 (Figs 90A, 91B, C); lateral wings slightly asymmetrical, similar in size; both wings with sensilla at distal tip (Fig. 91A). GS symmetrical, approximately 1.8 times longer than wide; anterior part dilated, with swelling on left side larger than on right; sensilla on apex of each, about 1.8 times longer than wide; swelling on left side hemispherical, swelling on right more conical (Figs 90A, 91F). P5 symmetrical (Fig. 90B), with small conical process at outer distal corner of CxP5, bearing short, strong, triangular sensilla, about 1.5 times longer than wide. BspP5 with long outer seta, about twice length of EnpP5. EnpP5 one-segmented. Exp 3-segmented; lateral spine of Exp2 as long as external margin of Exp3 (Fig. 91D); external seta of Exp3 reaching one third length of internal seta; internal seta almost reaching mid-length of terminal claw; terminal claw with comb of robust spinules in mid-section (Fig. 91E).

Figure 90. 

“Diaptomus” frutosae female. A Posterior pedigers and GS B P5.

Figure 91. 

“Diaptomus” frutosae female, SEM photographs. A Dorsal view of female (500 µm) B, C Posterior pedigers, GS and urosome, in dorsal view, showing details of spinular ornamentation along posterior margin of Ped4 (B = 100 µm, C = 200 µm) D P5 (100 µm) E Exp3P5 and terminal claw (20 µm) F GS, ventral view (100 µm).

The specimens were found in the middle part of the Paraná River (Fig. 92, RPAR-M2) and in the Yaciretá Reservoir (YACI-D). The species was relatively abundant in the samples and occurs in reservoirs and other water bodies near these locations, according to S. M. Frutos (pers. comm.). In a previous phylogenetic analysis, this species was placed close to the genus Scolodiaptomus Reid, 1987, which is monospecific [Scolodiaptomus corderoi (Wright, 1936)], because they share important features such as the subtriangular shape of Exp2P5R and the presence of modified setae or spinous processes on segments 13, 15 and 16 of the male A1R. However, it is very unlikely that “D.” curvatus belongs to the genus Scolodiaptomus, which is characterised by an unornamented hyaline lamella on segment 20 of A1R and by the presence of a dorsal cylindrical process on the Ped3. Again, the affinities of this species need to be tested as part of a comprehensive phylogenetic analysis of Neotropical diaptomids. It is likely that this species could be assignable to a new genus.

Figure 92. 

Geographical distribution of D. frutosae in de la Plata river basin.