Diaptomus frutosae, 2013

Perbiche-Neves, Gilmar, Boxshall, Geoff A., Paggi, Juan C., da Rocha, Carlos E. F., Previattelli, Daniel & Nogueira, Marcos G., 2013, Two new species of Diaptomidae (Crustacea: Copepoda: Calanoida) from the Neotropical Region (Paraná River), Journal of Natural History 47 (5 - 12), pp. 449-477 : 462-473

“ Diaptomus ” frutosae Perbiche-Neves and Boxshall , sp. nov.

( Figures 10 to 19)

Material examined

Holotype. One ♂, entire, alcohol + glycerine ( MZUSP 24480 ), Yacyretá Reservoir (27 ◦ 30 ′ 9.12 ′′ S; 56 ◦ 31 ′ 56.69 ′′ W), 15 km upstream from the dam, on border between Argentina / Paraguay.

Paratypes. Two ♂ ( MZUSP 24482 ) , 1 ♀ ( MZUSP 24481 ) , and 2 ♀ ( MZUSP 24483 ) , entire, alcohol + glycerine; 5♂ and 5♀ ( NHM-UK 2011.1202 - 1211 ) ; 2♂ and 2♀ (1932 INPA). All collected from Yacyretá Reservoir, border between Argentina and Paraguay, 28 February 2010 and 5 June 2010 .

Etymology

Named after Dr Margarita S. Frutos in honour of her many contributions to the study of Neotropical zooplankton.

Diagnosis

Male. Prosome with incomplete dorsal suture between pedigerous somites 4 and 5; plane of suture marked by dorsal row of spinules. Posterolateral wings of prosome symmetrical, each with small sensilla at apex. Genital somite asymmetrical; left side with semicircular expansion with sensilla at tip; right side smooth with sensilla located near posterolateral corner. Right caudal ramus larger than left. Chitinous protuberances present at base of modified seta on segment 13 of right geniculate antennule; small spinous processes present on segments 15 and 16; distinctive hook-like process present distally on segment 20 of right geniculate antennule, with chitinous protuberance on outer margin of hook. Second exopod segment of right leg 5 with distinctive subtriangular shape; lateral spine inserted in distal half of outer margin of segment, about 3.5 times smaller than terminal claw.

Female. Plane of suture between pedigerous somites 4 and 5 marked by presence of dorsal row of spinules; posterolateral wings on prosome asymmetrical, left wing forming semicircular expansion with sensilla at tip, and right wing more elongate with sensilla at tip, larger than on left side. Genital double-somite with asymmetrical lateral

margins; left margin with circular expansion and downwardly curved sensilla; right margin with smaller expansion with sensilla at tip. Caudal rami symmetrical.

Description – male

Prosome ( Figure 10A ). Body length 1,308 µm, maximum width 345 µm. Rostrum slightly asymmetrical, right filament broader than left ( Figures 12A ; 17A ). Plane of suture between pedigerous somites 4 and 5 marked dorsally by presence of row of spinules. Posterolateral wings in prosome symmetrical, each with small sensilla at apex.

Urosome ( Figure 10A ). Four-segmented, lateral margins of genital segment asymmetrical; left margin with semicircular expansion with sensilla at tip; right side smooth with sensilla located close to posterolateral corner.

Caudal rami ( Figures 10A ; 13F ). Asymmetrical. Right caudal ramus twice as long as broad; left caudal ramus 1.5 times longer than broad. Both rami with setules along inner margin. Caudal rami bearing six setae with normal ornamentation.

Right geniculate antennule ( Figures 11B ; 12A–I ). With 22 expressed segments, modified with enlarged segments in mid section. Formula of setae (s), conical setae (cs), long setae (ls), modified setae (ms), vestigial setae (vs), aesthetascs (ae) and processes (p) on each segment as follows: (segment 1) 1s + 1ae, (2) 3s + 1vs +1ae, (3) 1vs + 1ls + 1ae, (4) 1s, (5) 1s + 1vs + 1ae, (6) 1s, (7) 1ls + 1ae, (8) 1s + 1cs, (9) 1s + 1ls + 1ae, (10) 1s + 1ms, (11) 1s + 1ms, (12) 1s + 1cs + 1ae, (13) 1s + 1ms + 1ae, (14) 1s + 1ls + 1p + 1ae, (15) 1s + 1ls + 1p + 1ae, (16) 1sm + 1ls + 1p + 1ae, (17) 2ms + 1s, (18) 1ms + 2s, (19) 2ms + 1s + 1ls + 1ae, (20) 2s + 2ls + 1p, (21) 2ls, (22) 3ls + 1s + 1ae. Long seta on segment 7 with rounded apex, as in long seta on segment 9. Spinous processes of segments 10 and 11 normal, that on segment 11 longer than that on segment 10 ( Figure 12D ). Chitinous protuberances present at base of modified seta on segment 13, located on semicircular mound ( Figure 12E, I ); modified seta with minutely bifid apex, not reaching base of segment 14 ( Figure 12E, H ); very small process on segment 14, in contrast to segments 15 and 16 each with process of similar length. Modified setae on segments 15, 16 and 17 each with oblique tip. Segment 20 drawn out into large distal hook-like process with square base and chitinous protuberances near base; hook exhibiting size variation, reaching to tip of segment 22 in some specimens ( Figure 12A, B, F, G ).

Left antennule ( Figure 11A ). With 25 expressed segments, numbers of setae (s), conical setae (cs), long setae (ls), vestigial setae (vs) and aesthetascs (ae) on each segment, as follows: (segment 1) 1s + 1ae, (2) 3s + 1ae +1vs, (3) 1ls + 1ae + 1vs, (4) 1s, (5) 1ls + 1vs + 1ae, (6) 1s, (7) 1ls + 1ae, (8) 1s + 1cs, (9) 1s + 1ls + 1ae, (10) 1s, (11) 1ls, (12) 1s + 1cs + 1ae, (13) 1s, (14) 1ls + 1ae, (15) 1ls, (16) 1ls + 1ae, (17) 1s, (18) 1ls, (19) 1s + 1ae, (20) 1s, (21) 1ls, (22) 1s + 1ls, (23) 1ls + 1s, (24) 2ls, (25) 3ls + 1s + 1ae.

Antenna ( Figures 13E, G ; 17B, C ). Biramous; coxa with one seta; basis with two setae. Endopod two-segmented: first segment with two setae at mid-length, and row of 10–11 spinules distally, with pore next to row, compound distal segment with 15 setae, arranged in group of eight on inner lobe and distal group of seven, plus spinule row (five spinules). Exopod seven-segmented, setation as follows: 1, 3, 1, 1, 1, 1, 4; segment 2 with ancestral segments partially or totally separated on one side only.

Mandible ( Figure 14C ). Coxal gnathobase heavily sclerotized, cutting blade with subcaudal and triangular teeth, cutting surface with six multicusped teeth plus seta near toothed margin, with small denticles. Palp comprising basis with four setae, two-segmented endopod with four and nine setae, and two rows of spinules in mid part; exopod four-segmented with 1, 1, 1, 3 setae.

Maxillule ( Figure 14A ). Coxal epipodite with nine setae and row of spinules on distal surface. Coxal endite with four distal setae. Outer seta representing basal exite present; four setae on proximal basal endite, distal basal endite with four setae. Endopod twosegmented; with three setae on margin of proximal segment, and five distal setae on second segment. Exopod with six distal setae.

Maxilla ( Figure 14D ). Proximal praecoxal endite with five setae and one spine (setules present on these setae but not figured here); distal praecoxal endite with three setae: proximal and distal coxal endites each with three setae; allobasis with four setae; free endopod with five setae in total.

Maxilliped ( Figures 14B ; 17D, E ). First syncoxal endite represented by one seta with row of spinules at base; second to fourth syncoxal endites from proximal to distal with 2, 3, 3 setae, distal angle of syncoxa extended into lobe with row of small spinules; basis with three setae, double row of setules proximally; endopod six-segmented, with 2, 3, 2, 2, 1 + 1, 4 setae.

Swimming legs ( Figure 15 ). Exopods three-segmented; endopod three-segmented in legs 2–4 and two-segmented in leg 1; Schmeil’s organ present on second endopod segment of leg 2 ( Figure 15C ). Row of spinules present distally at base of terminal spine on endopod of each leg; setule rows present on basis of leg 1 ( Figure 17D ). Spine and seta formula as in Table 2.

Right leg 5 ( Figures 16D ; 18A–E ). Coxa wider than long; with distal semicircular projection on outer surface bearing reduced seta at tip. Basis 1.5 times longer than wide; with chitinous ridges running parallel to inner margin; bearing seta near outer distal corner. Endopod small, fused to basis and forming triangular process at inner distal corner of basis, ornamented with spinules. Exopod three-segmented; first segment wider than long; second segment longer than wide, with subtriangular shape; lateral spine small, similar in length to width of basis, and inserted distal to strong, almost right-angled curvature in outer margin; third segment represented by terminal claw 1.8 times longer than second segment, with row of small spinules along concave inner margin.

Left leg 5 ( Figures 16D ; 18D, F, G ). Coxa longer than wide; with robust seta on outer margin. Basis longer than wide; with thin seta on outer margin. Endopod onesegmented, as long as first exopod segment, ornamented with row of small spinules around apex. Exopod two-segmented; first segment with convex outer margin; inner margin with rounded process bearing setules; second segment with semicircular process bearing setules proximally on inner margin, inner spinulate spine and apical spinous process.

Description – female

Prosome ( Figures 10B ; 19A–C ). Body length 1346 µm, maximum width 348 µm. Body larger than male. Rostrum slightly asymmetrical, with paired filaments, right broader in mid part than left ( Figure 13B ). Prosome with incomplete dorsal suture separating fourth and fifth pedigerous somites, plane of suture marked by row of spinules dorsally and laterally ( Figure 19B,C ). Posterolateral wings of prosome small and slightly asymmetrical; left wing slightly larger than right and semicircular in shape; right wing elongate; both lateral wings tipped with spinous process.

Urosome ( Figures 10B ; 19B, C, E ). Three-segmented; genital double-somite asymmetrical; left lateral expansion much larger than right, with circular process anteriorly bearing posterolaterally directed spine on apex; right expansion small, elongate, slightly curved anteriorly, with spine on apex. External genital area ventral: delimited anteriorly by broad symmetrical opercular pad, and laterally by posteriorly directed lateral processes. Paired gonoporal plates located adjacent to midline, between lateral processes ( Figures 13C ; 19F ). Urosomite 2 about three times broader than long; urosomite 3 longer than broad and without projections.

Caudal rami ( Figure 10B ). Symmetrical; about 1.7 times longer than broad; with setule row along inner margin; caudal rami bearing six setae with normal ornamentation.

Antennule. Symmetrical; extending to tips of caudal setae; setal formula similar to that of left antennule of male.

Antenna, Mandible, Maxillule, Maxilla, Maxilliped, Swimming legs. As in male.

Leg 5 ( Figures 13D ; 19D, G ). Symmetrical, coxa with spinous process at outer distal corner carrying conical sensilla at tip; basis with curved outer margin, carrying long seta almost reaching end of first exopod segment. Exopod three-segmented; first segment larger than second, about two times longer than broad; second segment with lateral spine and drawn out into terminal claw, ornamented with rows of denticles bilaterally; small third segment offset, with two terminal setae, lateral about three times smaller than inner. Endopod one-segmented, with discontinuity in cuticle; armed with row of spinules at tip.

Geographical distribution of the new species

Both species were found in the middle stretch of the Paraná River. “ Diaptomus ” curvatus occurred along a stretch 1037 km in length and “ Diaptomus ” frutosae for about 500 km ( Figure 20 ). Old records for “ Diaptomus ” curvatus close to Santa Fé city ( Argentina) were made by Juan César Paggi in May 1972 (letter D in Figure 20 , Paraná River, near Villa Constitución: 33 ◦ 13 ′ 5 ′′ S, 60 ◦ 17 ′ 45 ′′ W), March 1981 (letter B, La Cuarentena Lake, Carvajal Island, Paraná River: 31 ◦ 42 ′ 42 ′′ S, 60 ◦ 37 ′ 56 ′′ W), and December 1993 (letter C, Coronda River, secondary channel of Paraná River: 31 ◦ 41 ′ 36 ′′ S, 60 ◦ 43 ′ 7 ′′ W). An additional record of D. frutosae was from the city of Corrientes in Argentina (letter A, Paraná River main channel, 27 ◦ 28 ′ 22 ′′ S, 58 ◦ 51 ′ 25 ′′ W), in a sample obtained by M. S. Frutos in 2010.

Other geographical coordinates are: YACI-Up: 27 ◦ 24 ′ 24 ′′ S, 56 ◦ 15 ′ 19 ′′ W; YACI-D: 27 ◦ 30 ′ 9 ′′ S, 56 ◦ 31 ′ 56 ′′ W; PAR-1: 28 ◦ 30 ′ 10 ′′ S, 59 ◦ 03 ′ 03 ′′ W; PAR-2: 30 ◦ 01 ′ 07 ′′ S, 59 ◦ 33 ′ 50 ′′ W; PAR-3: 31 ◦ 38 ′ 29 ′′ S, 60 ◦ 23 ′ 21 ′′ W.

Limnological parameters

The study of the Paraná River, from Yacyretá Reservoir to the end of the middle stretch (at Station PAR-3), revealed an increase in temperature, electrical conductivity, turbidity, total suspended solids, inorganic suspended solids, total nitrogen, total phosphorus, and chlorophyll a. In contrast there was a decrease in dissolved oxygen and transparency. Low values were found in the dam axis of Yacyretá Reservoir ( Table 3).

Figures

Figure 10. Dorsal habitus of “Diaptomus” frutosae sp. nov. (A) Male; (B) female.

Figure 11. “Diaptomus” frutosae sp. nov. male. (A) Left antennule; (B) right geniculate antennule.

Figure 12. Scanning electron micrograph of “Diaptomus” frutosae sp. nov. male. (A, B, F, G) Segment 20 of right antennule (A, B, F: 20 µm, G: 100 µm); (C) right antennule (400 µm); (D) segments 9–13 of right antennule (50 µm); (E) segments 13 and 14 of right antennule (50 µm); (H) segments 12–14 of right antennule (50 µm); (I) base of modified setae in segment 13 of right antennule (20 µm).

Figure 13. “Diaptomus” frutosae sp. nov. (A) Rostrum of male; (B) rostrum of female; (C) genital double-somite of female; (D) right leg 5 of female; (E) exopod of male antenna; (F) detail of right caudal ramus, ventral view; (G) male antenna, lacking exopod.

Figure 14. “Diaptomus” frutosae sp. nov. mouthparts. (A) Maxillule; (B) maxilliped; (C) mandible; (D) maxilla.

Figure 15. “Diaptomus” frutosae sp. nov., swimming legs of male. (A) Anterior view of last endopod segment of leg 2; (B) posterior view of last endopod segment of leg 2; (C) detail of Schmeil’s organ on second endopod segment of leg 2; (D) leg 1; (E) leg 2; (F) leg 3; (G) anterior view of last endopod segment of leg 3; (H) posterior view of last endopod segment of leg 3; (I) leg 4; (J) anterior view of last endopod segment of leg 4; (K) posterior view of last endopod segment of leg 4.

Figure 16. “Diaptomus” frutosae sp. nov. leg 5 of male. (A–E) Several views of leg 5.

Figure 17. Scanning electron micrograph of “Diaptomus” frutosae sp. nov. male. (A) Rostrum (20 µm); (B) left antenna (100 µm); (C) detail of the segment 1 and 2 of endopod of antenna (20 µm); (D) maxilliped (100 µm); (E) detail of distal syncoxal endite of maxilliped (20 µm).

Figure 18. Scanning electron micrograph of “Diaptomus” frutosae sp. nov. male. (A) Right leg 5 (300 µm); (B) right leg 5 (200 µm); (C) distal part of right leg 5 (200 µm); (D) left and right leg 5 (200 µm); (E) coxa, basis and segment 1 of exopod of right leg 5 (100 µm); (F, G) basis, endopod and exopod of left leg 5 (50 µm).

Figure 19. Scanning electron micrograph of “Diaptomus” frutosae sp. nov. female. (A) Habitus (500 µm); (B) detail of last segment of cephalothorax, genital double-somite and urosome (200 µm); (C) last segment of prosome and genital double-somite (200 µm); (D) leg 5 (100 µm); (E) genital double-somite (100 µm); (F) genital opening (50 µm); (G) detail of terminal claw of leg 5 (20 µm).

Figure 20. Geographical distribution of the two new species. The codes for the sampling sites provide a link to the limnological parameters given in Table 3.