Argyrodiaptomus paggii, Previattelli, Daniel & Santos-Silva, Edinaldo Nelson Dos, 2007

Previattelli, Daniel & Santos-Silva, Edinaldo Nelson Dos, 2007, A new Argyrodiaptomus (Copepoda: Calanoida: Diaptomidae) from the southwestern Brazilian Amazon, Zootaxa 1518, pp. 1-29 : 3-24

Argyrodiaptomus paggii n. sp.

Figs 1–21

Material examined: Holotype ď, dissected and mounted on slide in glycerin ( INPA 1451), Igarapé Boa Viagem, 08°43'45''S, 63°24'26''W, right tributary of Jamari river, 6 km upstream of Samuel hydroelectric dam, 47 km east of the city of Porto Velho, in the state of Rondônia, Brazil.

Paratypes: 5 ď dissected and mounted on slides in glycerin ( INPA 1445–1449); 5 Ψ dissected and mounted on slides in glycerin ( INPA 1440–1444); 50 Ψ and 50 ď ( INPA 1450) undissected, kept in 4% formalin. All collected from Igarapé Boa Viagem, State of Rondônia, Brazil, 0 2 Dec 1986 and 20 Aug 1987.

Diagnosis. Cephalosome with dorsal depression at suture, with a nucal organ broader than long (ratio = 3:2) and soft angles. Outer margin of A2, Enp 1, with patch of spinules (15 approx.). Group of spinules between first and second coxal endites of Mxp. Right basis of P5 of ď with 5 patches of spinules of similar number and shape. Exp 1 with expansion strongly sclerotized, located posteriorly at distal margin (projected over second segment); expansion with digitiform, blunt tip, larger than endopod and perpendicularly inserted to segment; ovoid process adjacent to expansion; outer distal region of segment with additional triangular expansion, terminally acute. Left basis of P5 of ď with 6 patches of spinules of similar number and shape. Spinose seta on P5 Exp 2 (left) of ď 4 times length of digitiform process. Enp of left P5 of ď with complete suture. Suture between Th4 and Th5 of Ψ incomplete dorsally. Ψ lateral wings symmetrical formed by 1 pair of lobes. Left lateral wing posteriorly directed, unarmed, inwardly curved over the GS, with posterior margin continuous with lateral wings. Dorsal lobes absent. Ornamentation composed by small, spiniform sensillum, 1 at each end of lobes. GS of Ψ symmetric, with lateral expansions at anterior portion. Ur2 of Ψ partially fused into the GS. Coxa of P5 of Ψ without conical process at posterior face. In same region, 1 small, spiniform sensillum with rounded apex. P5 Enp of Ψ long, as long as or longer than Exp-1, with complete, well-defined suture.

Description. Male (figs 1–15): Length of holotype, excluding caudal setae, 1887 µm. Mean length ď: 1856.8 µm (n = 20, s.d. = ± 40.7, range = 1794–1932 µm). Body smaller and more slender than Ψ. Widest region is at distal portion of Th2.

Cephalosome with incomplete dorsal suture. Modified region forming thin depression at suture level, with nucal organ broader than long (width/length ratio 3:2) and soft angles (fig. 2B). Rostrum with paired filaments; rostrum asymmetrical, with process on right side of basal part; defined from frontal margin of dorsal cephalic shield by complete suture; with pair of sensilla adjacent to suture (fig. 2A–B).

Prosome 5-segmented. Th4 and Th5 distinct, separated by complete suture. Lateral surface (dorsal view) of the suture deeper than on medial region. Th5 smaller and more curved than on the posterior edge, also bearing a small spine on each posterior side of the dorsal extremity. Hyaline frill between Th5 and GS. Lateral wings formed by 1 pair of lobes. Lateral wings posteriorly directed, without spines. Ornamentation composed by spiniform sensilla, 1 at each end of lobes.

Urosome formed by 4 urosomites, followed by the anal somite and caudal rami. Genital somite asymmetrical, with 2 sensilla, 1 at right/posterior region and 1 at left/posterior region, more medial than right. Genital aperture on ventral/lateral posterior corner of GS on left side. Caudal rami symmetrical, longer than wide, with 6 setae; setules along medial margin.

Antennules asymmetrical, extending beyond prosome but not extending past distal portion of second urosomite. Ancestral segments II–IV, XXI–XXIII, XXIV–XXV and XXVII–XXVIII completely fused. Tip of setae on segments 3 (V), 7 (IX), 9 (XI) and 14 (XVI) acute.

Right A1 22-segmented (figs 3 & 5), geniculate between segments 18 and 19. Number of armature elements presented in table 2. In posterior view, for segment 8–12, space between each segment obtuse relative to the

other segments, hyaline membrane also present (fig. 5B–C). In anterior view this membrane is smaller and space is parallel relative to the other segments. Posterior surface of segment 12 with incomplete cuticle, partially separating the internal region of the surface (fig. 5B–C). Segment 13 with grooves at posterior surface (fig. 5C). Modified region (posterior view) comprising segments 13 (XV) to 18 (XX). Widest region at segment 14 (XVI), longer at segment 19 (XXI–XXIII). Segment 3 (V) with 1 aesthetasc. Segments 4 (VI), 14 (XVI), 15 (XVII), 16 (XVIII) and 17 (XIX) with outer margin ornamented with thin tubercles. Vestigial setae on segments 2 (III), 3 (V) and 5 (VII). Segments 8 (X) and 12 (XIV) with small conical setae (smaller than modified setae of segments 10 (XII) and 11 (XIII)), forming a strong spiniform process. Conical seta of segment 8 smaller than conical seta of segment 12. Segments 10 and 11 with modified setae parallel to main axis of antennule. Seta of segment 11 larger than seta on segment 10, but smaller than modified seta of segment 13 (XV). Segment 11 with 1 aesthetasc. Modified seta on segment 13 different from modified setae on segments 17 (XIX), 18 (XX) and 19 (XXI–XXIII), forming a strong process, reaching or exceeding the distal margin of the next segment (14). Tip of modified seta acute. Spinouse process at outer margin of segment 15 (XVII) always present. Segments 17 (XIX) and 18 (XX) with 1 seta-like aesthetasc. Segment 18 with modified seta of similar size to the aesthetasc. Segment 19 (XXI–XXIII) with distal seta, as long as or longer than segment size. Segment 20 (XXIV–XXV) with 2 setae inserted posteriorly, process on distal margin always present. Process curved, not exceeding half the length of the next segment. Segment 21 (XXVI) with seta inserted ventrally.

Left A1 25-segmented (fig. 4). Number of armature elements as shown in table 2. Segment 11 (XIII) with single seta. Modified setae on segments 8 (X) and 12 (XIV) similar to those on corresponding segments of right A1. One of the setae of segments 22 (XXIV) and 23 (XXV) inserted dorsally on distal inner margin. Seta of segment 24 (XXVI) inserted ventrally at distal outer margin.

A2 biramous (fig. 6A–B). Coxa with inner seta. Basis with 2 setae on the inner face, inserted posteriorly. Exopod 8-segmented; second (II–IV) and penultimate (IX–X) segments compounded with regions of discontinuous cuticle surface, forming grooves; penultimate segment elongated; distal segment small, with 3 long, apical setae. Endopod 2-segmented; outer margin of first segment ornamented with 1 patch of spinules (approx. 15); inner margin with 2 setae and pore between patch of spinules and setae; second segment bilobed, with groove between lobes; outer lobe with 7 distal setae and 1 group of spinules on dorsal/outer margin; inner lobe with 8 distal setae.

Mandible divided into praecoxa, coxa, basis, Enp and Exp (fig. 6C). Gnathobase strongly sclerotized, transformed into a prominent lobe on caudal margin. Gnathal blade separated from lobe by deep diastema, with 1 sub-triangular tooth plus 6 multicuspidal teeth (fig. 6C & E). Dorsal seta unique, inserted at apical margin. Mandibular palp biramous. Basis of the palp with 4 inner setae (3 distal). Exp with 4 segments; setal formula 1, 1, 1, 3. Enp 2-segmented; first segment with distal lobe and 4 setae; second segment with 7 distal setae and 3 patches of spinules on posterior margin (1 line situated sub-terminally, 1 patch on outer margin and 1 distal: fig. 6D).

Mxl (fig. 7A) praecoxal arthrite bearing 10 marginal setae, 2 armed with sub-distal spines; sub-marginally, 5 setae inserted—4 naked, 1 spinulated. Epipod of coxa bearing 9 setae; coxal endite with 4 distal setae. Basal exite represented by outer seta; basal proximal endite well defined, with 4 setae. Distal endite fused with basis, with 4 setae and row of marginal spinules. Exp fused, bearing 6 distal setae and a group of spinules on anterior surface. Enp 2-segmented; first segment with 3 distal setae, Enp-2 with 5 setae and row of spinules on anterior surface (fig. 7B–C).

Mx (fig. 8) with praecoxa and coxa fused medially, separated laterally. Proximal praecoxal endite with 5 setae and 1 spine. Distal praecoxal endite naked. Coxal endites with 3 setae and distal row of spinules. Allobasis well developed, bearing 4 setae. First endopod partially segmented, with a lobe on posterior surface. Endopod 3-segmented with 5 setae (1, 1, 3).

Mxp well developed, comprising syncoxa, basis and 6 free endopod segments. Praecoxal endite with 1 seta and a group of spinules on posterior surface. Coxal endites not developed, represented by 8 setae, distributed in 3 medial patches. Setal formula: 2, 3, 3 (fig. 9A). Ornamentation: proximal group of setules adjacent to the group of setae on first coxal endite, 1 group of spinules between first and second coxal endites, 1 group of spinules (longer and more numerous than previous), on anterior surface of the second coxal endite, adjacent to setal group, 1 group of setules between the groups of setae of first and second coxal endites. Distal angle of syncoxa with setules along margin. Basis with 3 setae at medial margin (fig. 9B). Ornamentation represented by row of sub-medial spinules on one side and setules on the other. Enp-1 distinct but reduced. Setal formula of the endopod as: 2, 3, 2, 2, 1 + 1, 4.

P1–P4 symmetrical and biramous. Armature formula in table 3.

P1: Coxa with setules on inner margin; no spines on posterior surface. Basis with setules at proximal margin (fig. 10A & C). Exp 3-segmented (fig. 10A); setules along inner and outer margins of all segments. Exp-3 spine with cirrose apex (fig. 10A), anterior surface Exp-3 with line of spinules. Enp 2-segmented; setules present along all outer margins and inner margin of second segment (fig. 10D).

P2: Lateral and posterior portion of basis smooth (not ornamented with setules). Exp 3-segmented; setules along inner and outer margins of all segments (fig. 10B). Anterior surface Exp-3 with distal row of spinules (fig. 10F). Enp 3-segmented. Schmeil's organ present on posterior surface of segment 2. Setules along outer margin of all segments and at inner margin of segments 2 and 3 (fig. 10E). Enp-3 anterior surface with 2 distal rows of spinules. Groups of spinules in different sizes and numbers (distal ones larger, but less numerous than proximal ones) (fig. 10G).

P3: Setules along inner margin of all segments and on outer margin of segments 2 and 3 (fig. 11A). Anterior surface of Enp-3 with 2 lines of spinules at distal portion. Groups of spinules with different sizes and numbers (distal ones larger, but less in number than proximal ones) (fig. 11E). Remaining characteristics similar to P2.

P4: Basis with seta on posterior surface. Exp 3-segmented. Setules on inner margin of all segments and outer margin of segments 2 and 3 (fig. 11B). Anterior surface of Exp-3 segment with 1 line of spinules at distal portion (fig. 11G). Enp with 3 segments. Setules on outer margin of all segments and inner margin of segments 2 and 3 (fig. 11F). Anterior surface of Enp-3 with 2 lines of spinules on distal portion. Groups of spinules with different sizes and numbers (distal ones larger, but fewer than proximal ones) (fig. 11H).

P5 asymmetrical, biramous (figs 12–15). Intercoxal plate (coupler) as long as it is wide, equally wide as coxa, inserted laterally (not overlapping plate).

Right P5: Rudimentary praecoxa present. Coxa with conical process, posteriorly directed, not projected above basis. Conical process reduced. Apex of the process with small sensillum, acute at tip. Basis without expansion on posterior surface. Posterior surface with oblique groove, ornamented with small spinules along distal rim. Inner margin ornamented with small spinules, forming patches of similar number and shape (fig. 13). Seta of outer margin inserted posteriorly. Semicircular lamella present on inner margin of basis. Exp 2- segmented. First segment cylindrical; expansion strongly sclerotized, located posteriorly at distal margin (projected over the second segment); expansion digitiform, blunt tip, larger than Enp and inserted perpendicularly inserted to the segment; ovoid process adjacent to the expansion; outer distal region of segment present another expansion with triangular shape and acute apex. Enp-2 wide and sub–triangular; lateral spine straight; length of spine reaching between half and 2/3 of terminal claw; ornamentation composed by 1 row of spinules along inner margin. Terminal claw strong, inserted distally, curved in tree planes. Presence of a row of spines from second half of the inner margin; apex acute and curved. Enp distinct from basis, with 2 incompletely separated segments; distal portion of segment 2 ornamented with terminal spinules, arranged in crown on anterior inner surface (fig. 13E).

P5 left: well developed, reaching distal margin of right Exp-1 (fig. 12). Coxa with a small conical process (smaller than on the right coxa), directed posteriorly directed, on distal outer margin; apex of conical process with sensillum similar to that on right coxa, but smaller. Basis with seta on outer margin; inner margin lightly curved; inner surface with spinules, forming similar patches but different from those on right basis (fig. 14). Exopod 2-segmented; first segment sub–triangular, outer margin curved; semicircular process on inner margin armed with long setules; second segment with inner margin expanded; ornamented with setules and a group of spinules; distal portion with digitiform process strongly sclerotized; process ornamented with small number of spinules; spiniform seta well developed, distally inserted on anterior surface, reaching far beyond (more than double) digitiform process; length ratio of length/width of spinulouse seta 4:1. Endopod conical; 2-segmented, suture complete; proximal portion ornamented with distal row of spinules; segment 2 as long and as wide as segment 1 (fig. 15).

Adult Ψ (figs 16–21): Length excluding caudal setae: 2070 µm. Mean length Ψ (n=20) 2068.3 µm, s.d. ± 48.6, range = 1955–2150 µm. Body wider and longer than ď, widest at distal portion of Th2.

Cephalosome with dorsal suture incomplete; modified region forming a thin depression at suture level, with nucal organ broader than long (ratio = 3:2) and soft-shaped angles (figs 16A & 17A). Rostrum broader than in ď, with paired filaments; symmetrical; defined from frontal margin of dorsal cephalic shield by complete suture; presence of pair of sensilla adjacent to suture (fig. 17B).

Prosome 5-segmented. Th4 and Th5 distinctly defined; suture between them incomplete in dorsal surface; in lateral view, suture conspicuous. Hyaline frill between Th5 and GS. Lateral wings symmetrical, formed by single pair of lobes; left lateral wing posteriorly directed, without spines, inwardly curved against GS, with posterior margin continuous with lateral wings. Dorsal lobes absent. Ornamentation including small spiniform sensilla, one at each extremity of the lobes and sensilla distributed as shown in figure 16A.

Urosome with 2 somites followed by the anal somite and caudal rami. Genital somite saddle shaped at lateral view longer than wide, covering the other urosomites. Lateral sensillum on each side (dorsal view), small and acute at apex. Integument reduced ventrally. Outer genital area delimited by large, symmetrical operculum. Lateral processes well developed, posteriorly directed, with area of flexible cuticle, adjacent to the opercular area. Gonoporal plates located medially between lateral processes (fig. 18). Second urosomite small, partially fused, telescoped and covered by GS. Anal somite with operculum not completely covering the anal opening and with 1 sensillum on each side. Caudal rami symmetrical, 2.5 times longer than wide, with setules along inner margins (fig. 18B).

Antennules: symmetrical, 25-segmented, armature and structure similar to ď left antennule. Antennules extending beyond prosome, but not reaching beyond half of the genital somite. Number of armature elements as in table 2.

P5 (figs 19–21) symmetrical. Coxa without conical processes on posterior surface, coxa with small, spiniform sensillum with rounded apex. Sub-triangular basis (outer margin smaller than inner margin) with seta on outer margin, seta not reaching beyond half the length of Exp-1. Exp-1 segment longer than Exp-2. Exp-2, right, armed with lateral spine (most species do not have this ornament) (figs 19A & 20). Segment 3 distinct, armed with 2 setae; medial seta reaching beyond half the length of terminal claw; lateral seta not reaching beyond half of medial seta; terminal claw symmetrical, straight, with row of lateral/medial spinules. Enp with 2 long segments, as long or longer than Exp-1; suture between segments well defined; distal portion of second segment with 2 rows of setae and subterminal crown of spinules; setae with different length, 1 of them equal or more than 2/3 length of the other.

Distribution. only known from the type locality (fig. 22). As mentioned above, the scarcity of information on the distribution of freshwater copepods from this region prevents us from speculating on the potential distribution of the species. In samples collected from the same river, in an adjacent locality, Notodiaptomus coniferoides ( Wright, 1927) and one species of Rhacodiaptomus Kiefer, 1973 ( R. besti Santos-Silva & Robertson, 1993 ) were found. More studies are needed to define the real distributional limits of these species.

Etymology. The species is named in honor of the Argentinean copepodologist Dr. Juan Cesar Paggi, one of the most important specialists in Latin America, for his overall contribution to the knowledge of the freshwater copepods in South America.

Figures

FIGURE 1. Argyrodiaptomus paggii n. sp., ♂ adult: A – habitus, dorsal view. B – habitus, left lateral view.

FIGURE 2. Argyrodiaptomus paggii n. sp., ♂ adult, scanning electron microscopy (SEM): A – habitus, dorsal view. B – Cephalosome, dorsal view. C – rostrum, ventral view.