Pseudovaigamus tridentatus, Narciso & Perbiche-Neves & Silva, 2020

Narciso, Rodrigo B., Perbiche-Neves, Gilmar & Silva, Reinaldo José Da, 2020, A new species of Pseudovaigamus Amado, Ho & Rocha, 1984 (Cyclopoida Ergasilidae) from the teleost Pimelodus maculatus Lacepède, 1803, Zootaxa 4881 (2), pp. 349-360 : 351-357

Pseudovaigamus tridentatus n. sp.

( Figs 1–4 )

Host. Pimelodus maculatus Lacepède, 1803 ( Siluriformes : Pimelodidae ).

Locality. Paranapanema River , Jurumirim Reservoir, Upper Paranapanema River (23° 29’16.54” S, 48° 37’12.88” W), municipality of Angatuba, S „o Paulo State, Brazil .

Additional locality. Veados River , Jurumirim Reservoir, Upper Paranapanema River (23° 16’2.49” S, 48° 38’15.72” W), municipality of Itatinga, S „o Paulo State, Brazil .

Site in host. Gill.

Specimens deposited. Holotype MZUSP 41553 (adult female) and Paratypes MZUSP 41554 to MZUSP 41562 (9 adult females) in the the Zoological Collection of the Museu de Zoologia da Universidade de S„o Paulo ( MZUSP), municipality of S„o Paulo, S „o Paulo State, Brazil; and Paratypes INPA 2531 to INPA 2534 (5 adult females) in the Invertebrate Collection of the Instituto Nacional de Pesquisas da Amazônia ( INPA), municipality of Manaus, Amazonas State, Brazil .

Prevalence and mean intensity on the gill filaments: eight of 91 analyzed fish (or 8,8%) and 4,2 ± 1,8 (1–14) copepods per infected fish.

Etymology. The specific name is derived from the Latin word, tridentis (= trident) in reference to the trifid rostral spine that resembles the cutting edge of that old melee weapon.

Differential diagnosis. Trifid rostral spine, armed with a long middle spine and two curved lateral spines. Retrostylets with the innermost portion extending posteriorly to form a spatulate process. Antennule 5-segmented; first segment with a groove on posterior margin. Caudal rami simple, lacking any distal lobe. Second endopodal segment of P1 and third exopodal segment of P1–P2 armed with dilated spine.

Description of adult female. Based on 15 adult females, no males observed. Body cyclopiform ( Fig. 1A ), comprising prosome, urosome, and caudal rami; prosome consisting of cephalosome and PS-1; PS-1 fused to cephalosome; and three free pedigerous somites (PS-2 to PS-4). Cephalothorax bullet-shaped ( Fig. 1A ), decreasing in width anteriorly, maximum width at level of restrostylet tip ( Table 2 ); dorsal surface with several pores and bristles symmetrically distributed and one circular integumental window (located at level of rostrum’s middle spine) (arrowed in Fig. 1A ); and armed with paired dorsolateral stylets (= retrostylets). Rostrum forming trifid rostral spine and ornamented with several pores and bristles on ventral surface ( Fig. 1B ); middle spine long, about three times longer than lateral spines, straight and sharply posteriorly; lateral spine strongly curved, with sharp tip. Retrostylets double ( Fig 1C ) carrying lateral stylet process and medial spatulate process; stylet process slightly curved, with sharply tip; spatulate process slightly longer than stylet, with rounded tip; dorsal surface ornamented with two bristles on lateral margin and one medial pore. Free pedigerous somites decreasing gradually in width from anterior to posterior ( Fig. 1A ); PS-2 with paired integumental windows laterally on tergite (arrowed in Fig. 1D ); dorsal surface ornamented with central pair of pores and two bristles on both lateral margins; PS-3 lacking any integumental window, dorsally ornamented with central pair of pores and three bristles on both lateral margins; PS-4 lacking any integumental window, central pores absent, dorsally ornamented with one bristle on both lateral margins.

Urosome consisting of PS-5, genital double-somite, and three free abdominal somites (AS-1 to AS-3) ( Fig. 2A ). PS-5 reduced ( Fig. 2A ), shorter and narrower than prosome somites, unornamented. Genital double-somite ( Fig. 2A ), about 1.5 times wider than long, bearing slit-like genital apertures dorsally, ornamented with posterior spinules on both lateral margins. Abdominal somites decreasing in width from anterior to posterior, each somite ornamented with posterior spinules on both lateral margins; AS-3 (= anal somite) deeply incised posteriorly (= anus), ornamented with pair of pores on dorsal surface; pores located immediately next to anus ( Fig. 2A ).

Caudal rami ( Fig. 2A ) about 1.5 times longer than wide; each ramus ornamented with one spinule on posterolateral margin (located immediately next to seta 1), and armed with four bare setae: seta 1 and 3 shortest, both setae inserted on ventral surface; seta 2 and 4 both inserted on posterior margin; seta 4 longest, about 2 times longer than seta 2 ( Table 2 ).

Antennule 5-segmented ( Fig. 1F ); first segment with groove on posterior margin; setal formula: 10, 4, 4, 2, 7 (total 27; aesthetascs not distinguished from setae). Antennna 4-segmented ( Fig. 1E ) comprising coxobasis and 3segmented enp; coxobasis (= first segment) broad, ornamented with bare seta; enp-1 (= second segment) longest, about 2 times longer than other antennary segments, straight, unornamented; enp-2 (= third segment) straight, unornamented; enp-3 (= fourth segment) reduced, unornamented; and one terminal claw; claw strongly curved, with fossa on concave margin (arrowed in Fig. 1E ).

Buccal apparatus ( Fig. 2C ) comprising mandible, maxillule, and maxilla. Mandible armed with two blades (anterior and posterior blade); anterior blade widening distally, unornamented; posterior blade longer and thinner than previous blade, unornamented. Maxillule rounded, unornamented. Maxilla 2-segmented, comprising syncoxa (= first segment) and basis (= second segment); syncoxa broad, with subdistal pore (located immediately next to basis’s insertion) (arrowed in Fig. 2C ); basis narrowing distally, ornamented with multiple spinules.

P1 to P4 biramous ( Figs. 3 A–D), each leg comprising coxa, basis, endopod (= inner ramus), and exopod (= out-er ramus). P1 ( Fig. 3A ); coxa ornamented with outer spinules; basis armed with bare outer seta; enp 2-segmented, both segments lacking any ornament on both margins; enp-1 (= proximal segment) armed with one plumose seta on inner margin; enp-2 (= distal segment) slightly longer than previous segment, armed with two distal spines (outer and inner spine); outer spine wider posteriorly, with rounded tip; inner spine about 1.5 times longer than previous spine, curved, with sharp tip; and five plumose setae on inner margin; exp 3-segmented, all segments lacking any ornament on both margins; exp-1 (= proximal segment) about 1.5 times longer than following segments, lacking any armament on outer margin; exp-2 (= middle segment) armed with one plumose seta on inner margin; exp-3 (= distal segment) armed with two spines (outer and inner spine); outer spine curved, with sharp tip; inner spine about 1.5 times longer than previous spine, wider posteriorly, with rounded tip; and five plumose setae on inner margin.

P2 ( Fig. 3B ); coxa ornamented with two outer spinules; basis armed with bare outer seta; enp 3-segmented; enp-1 (= proximal segment) ornamented with bristles along outer margin, armed with one plumose seta on inner margin; enp-2 (= middle segment) unornamented, armed with two plumose setae on inner margin; enp-3 (= middle segment) unornamented, slightly rounded, armed with single distal spine; spine curved, with sharp tip; and four plumose setae; exp 2-segmented, all segments lacking any ornament on both margins; exp-1 (= proximal segment) about 1.5 times longer than following segments, armed with single distal spine on outer margin; exp-2 (= middle segment) armed with one plumose seta on inner margin; exp-3 (= distal segment) armed with single distal spine; spine wider posteriorly, with rounded tip; and six plumose setae.

P3 ( Fig. 3C ) with same ornamentation and armament described for P2, except for exp-3 that on P3 lacks any spine.

P4 ( Fig. 3D ); coxa ornamented with two outer spinules, basis with bare outer seta; enp 3-segmented, all segments lacking any ornamented on both margins; enp-1 (= proximal segment) lacking any spine or seta on both margins; enp-2 (= middle segment) armed with minute spine on outer margin; spine smaller than those present on previous legs; and two plumose setae on inner margin; enp-3 (= distal segment) armed with two minute spines and three plumose setae; exp 2-segmented, both segments lacking any ornamented on both margins; exp-1 (= proximal segment) armed with minute spine on outer margin; exp-2 (= distal segment) armed with two minute spines and five plumose setae.

P5 reduced and represented by two bare setae (= ventrolateral and dorsal seta) ( Fig. 2A ); ventrolateral seta bigger and longer than dorsal seta; dorsal seta inserted on dorsal surface. Spine and setal formula of biramous legs is presented in Table 3 .

Intercoxal sclerites slender, unornamented, with both ends directed posteriorly ( Fig. 2B ). Intercoxal plates from P1 to P3 ornamented with spinules on lateral margins ( Fig. 2B ); intercoxal plate of P4, absent ( Fig. 2B ).

Egg sacs paired, uniseriate ( Fig. 4 ). Number of eggs per sac ranging from 3 to 6. First and last eggs in each sac differ from intermediate eggs; first and last eggs subtriangular, about 1.5 times longer than wide; intermediate eggs thinner than previous eggs, subrectangular ( Fig. 4 ).

Remarks. The new copepod was identified as a member of the Ergasilidae family by having: uniramous 4segmented antennae comprising coxobasis (= first segment), 3-segmented enp (= second to fourth segments) and terminal claw; mandible bearing two blades; maxilla 2-segmented with basis (= second segment) ornamented with distal spinules; and P4 exp 2-segmented. Furthermore, it was also recognized as a member of this family based on the absence of maxillipeds on parasitic adult females ( Boxshall & Halsey 2004). Within the Ergasilidae , the new copepod can be readily distinguished from other ergasilids, with exception of those of the vaigamid subgroup (i.e. monophyletic group within Ergasilidae composed of five genera: Gamidactylus , Gamispatulus , Gamispinus , Pseudovaigamus , and Vaigamus ), in having the combination of a 2-segmented enp for P1 and cephalothorax armed with a pair of dorsolateral retrostylets ( Narciso & Silva 2020).

Among the five vaigamid genera, the new copepod was identified as a new member of the monotypic genus Pseudovaigamus for possessing P4 with 3-segmented enp and 2-segmented exp (rather than P4 with 2-segmented enp and 1-segmented exp as in other vaigamid species). Additionally, the new copepod was also identified as a member of Pseudovaigamus since it shares with the type-species, P. spinicephalus , the following combination of features: (1) rostrum armed with rostral spine (rather than rostrum lacking rostral spine as in members of Gamidactylus and Gamispinus ); (2) antenna armed with single terminal claw (rather than two terminal claws as in members of Gamidactylus , Gamispatulus , and Gamispinus ); and (3) second and third antennary segments unornamented (rather than carrying multiple spinules on inner and/or outer margin as in members of Gamidactylus , Gamispatulus , and Gamispinus ). Although Pseudovaigamus shares several similarities with Vaigamus , the segmentation pattern of P4 (described above) exhibited by Pseudovaigamus species (including the new species described herein) allows the differentiation between the two genera ( Amado et al. 1995).

The new copepod Pseudovaigamus tridentatus n. sp. differs from its congener in several features. The rostral spine present in P. tridentatus n. sp. is trifid (comprising long and straight middle spine, and two lateral curved spines), whereas in P. spinicephalus it is simple (or carrying only the middle spine). The number of antennule segments is different: in P. tridentatus n. sp. antennule is 5-segmented, whereas in P. spinicephalus it is 6-segmented. Moreover, the rostral spine in P. spinicephalus is characterized by having a subbasal swelling which is absent in the new species. The morphology of retrostylets is also different: in Pseudovaigamus tridentatus n. sp. the innermost portion of this structure extends posteriorly forming a “spatulate” process similar in size to the stylet, whereas in P. spinicephalus , even though it carries a similar process (not quoted in the text of the original description), the spatulate process in this species is much smaller than the stylet (see Fig. 5 for a comparison). Another difference between both species is the morphology of caudal rami: in P. spinicephalus each ramus carries a distal lobe covered with multiples spinules, such lobe was not seen in the new species ( Fig. 2A ). Finally, the armature of legs in P. tridentatus n. sp. differs in several aspects from those present in P. spinicephalus , as follow: (1) coxa from P1 to P4 carries one or two lateral spinules in P. tridentatus n. sp. vs coxa unornamented as in P. spinicephalus ; (2) P1 exp-1 lacks any spine on outer margin in P. tridentatus n. sp. vs carrying one distal spine on outer margin as in P. spinicephalus ; (3) distal spines from P1 to P3 exp-3 and P1 enp-2 become wider distally in P. tridentatus n. sp. vs spines narrowing posteriorly and with sharp tip as in P. spinicephalus ; and (4) P4 enp-1 lacks any armature element (e.g. spine and/or seta) in P. tridentatus n. sp., whereas in P. spinicephalus it carries one plumose seta on inner margin (see Fig. 34 in Thatcher & Robertson 1984). Based on the morphological differences described above, we propose herein a new species, P. tridentatus n. sp., to the ergasilid genus Pseudovaigamus .

Figures

FIGURE 1. Pseudovaigamus tridentatus n. sp.—adult female. A body, dorsal view, cephalosome with circular integumental window (arrowhead). B rostral spine, ventral view. C retrostylet, dorsal view. D second pedigerous somite, dorsal view, with paired integumental windows laterally on tergite (arrowhead). E antenna, antennary claw with fossa on concave margin (arrowhead). F antennule. SpP = spatulate process. Stp = stylet process. Scale bars in µm.

FIGURE 2. Pseudovaigamus tridentatus n. sp.—adult female. A urosome, dorsal view. B intercoxal sclerites and intercoxal plates, ventral view. C buccal apparatus. is1 to is4 = first to fourth intercoxal sclerites. ip1 to ip3 = first to third intercoxal plates. P5 = fifth leg. S1 = seta 1. S2 = seta 2. S3 = seta 3. S4 = seta 4. Scale bars in µm.

FIGURE 3. Pseudovaigamus tridentatus n. sp.—adult female. A leg 1. B leg 2. C leg 3. D leg 4. Scale bars in µm.

FIGURE 4. Pseudovaigamus tridentatus n. sp.—adult female: variation in the number and format of eggs Scale bars in µm.

FIGURE 5. Morphological variation of retrostylets in vaigamid genera. A Gamispatulus schizodontis Thatcher & Boeger, 1984 from Thatcher & Boeger (1984a), with spatulate process (seta). B Gamispinus diabolicus Thatcher & Boeger, 1984 from Thatcher & Boeger (1984b). C Gamidactylus piranhus Thatcher, Santos & Brasil-Sato, 2008 from Thatcher et al. (2008). D Vaigamus retrobarbatus Thatcher & Robertson, 1984 from Thatcher & Robertson (1984), with innermost portion extending posteriorly (seta). E Pseudovaigamus spinicephalus (Thatcher & Robertson, 1984) from Thatcher & Robertson (1984), with innermost portion extending posteriorly (seta). F Pseudovaigamus tridentatus n. sp., with innermost portion extending posteriorly (seta). Scale bars in µm.

Tables

TABLE 2. Measurements in micrometers (µm) of adult females of Pseudovaigamus tridentatus n. sp.

Character	Range (mean)
Total length a	362–383 (392)
Cephalothorax length	180–225 (200)
Cephalothorax width	153–185 (164,5)
Rostral spine length	55–67 (62)
Retrostylet length	65–79 (73)
Antennule length	91–108 (101)
Antenna segment 1 length	36–61 (52)
Antenna segment 2 length	87–100 (95)
Antenna segment 3 length	45–52,5 (48)
Antenna segment 4 length	7–10 (9)
Claw length b	55–64 (59)
Pedigerous somite 2 length	38–56 (43)
Pedigerous somite 2 width	110–124 (117)
Pedigerous somite 3 length	30–44 (38)
Pedigerous somite 3 width	85–95 (91)
Pedigerous somite 4 length	23–31 (25,5)
Pedigerous somite 4 width	55,5–68 (62)
Pedigerous somite 5 length	10–21 (14)
Pedigerous somite 5 width	44–61 (52)
Genital double-somite length	36–47 (41)
Genital double-somite width	59–65 (62)
Abdominal somite 1 length	9,5–13 (11)
Abdominal somite 1 width	36–42 (39)
Abdominal somite 2 length	10–12,5 (11)
Abdominal somite 2 width	32–40 (36)
Abdominal somite 3 length	11–15 (13)
Abdominal somite 3 width	28,5–36,5 (33)
Caudal ramus length	19–22,5 (21)
Caudal ramus width	12–16 (14)
Caudal ramus seta 1 length	7–12 (9,5)
Caudal ramus seta 2 length	47,5–67 (60)
Caudal ramus seta 3 length	8–12 (9)
Caudal ramus seta 4 length	116–141 (129)
Egg sac length	192–312 (258)
Egg sac width	66–78 (73)