Argulus pestifer Ringuelet, 1948 (Figure 9) A. pestifer: RINGUELET (1948): 285–289, fIG. 1, PL. I fIGS. 1–5; LEMOS DE CASTRO (1985): 10, fIGS. 24–26; THATcHER (2006): 393, 395, 398, fIG. 9.30. Type host. Salminus maxillosus (= S. brasiliensis [Cuvier 1816]) (Ringuelet 1948). Type locality. Ibicuycito, municipality of Entre Rios, Argentina (Ringuelet 1948). Other hosts and localities. P. fasciatum, P. tigrinum, Amazon River Basin, in Janaucá Lake, state of Amazonas, Brazil (Malta 1983); P. fasciatum, P. tigrinum, Ichilo and Beni Rivers, Bolivian Amazon River Basin, Bolivia (Mamani et al. 2004); P. corruscans, Upper Parana River, Brazil (Takemoto et al. 2009); P. corruscans, Middle Parana River, Argentina (Chemes & Takemoto 2011). Material deposited. 28 vouchers: 1 adult male ZUEC-CRU 3509, 2 adult females ZUEC-CRU 3508, in ethanol 70%, 2 adult females ZUEC-CRU 3499, 3500, in Hoyer’s medium, 4 July 2008, 3 adult females ZUEC- CRU 3510, 3512, 2 adult males ZUEC-CRU 3511, in ethanol 70%, 5 July 2008, 2 adult females MZUSP 36234, in ethanol 70%, 7 July 2008, 3 adult females ZUEC-CRU 3514, in ethanol 70%, 5 July 2009, 1 adult female ZUEC- CRU 3513, in ethanol 70%, 8 July 2009 Pseudoplatystoma corruscans, skin and gills, Cuiabá River, Parque Nacional do Pantanal Matogrossense, Mato Grosso, Brazil (17°49′37.77″ S, 57°22′53.38”W); 1 adult male INPA 2310, in ethanol 70%, 3 June 2004, Pseudoplatystoma reticulatum, skin, Paraguay River, Corumbá, Mato Grosso do Sul, Brazil (18°59'53.17"S, 57°36'44.43"O); 1 adult male MZUSP 36230, 3 adult females MZUSP 36233, in ethanol 70%, 8 July 2009, Pseudoplatystoma reticulatum, skin, Cuiabá River, Parque Nacional do Pantanal Matogrossense, Mato Grosso, Brazil (17°49′37.77″ S, 57°22′53.38”W); 7 adult females INPA 2311, in ethanol 70%, 3 June 2004, Salminus brasiliensis, skin and gills, Cuiabá River (off Parque Nacional do Pantanal Matogrossense), 17°54'12.55"S, 57°27'14.74"O. Measurements. Based on 6 males and 26 females. Total length (mm) 3.4 (2.5–4.05) in males, 6.45 (2.9–10.7) in females. Carapace length 2.6 (1.8–3.1) in males, 5.1 (2.5–9) in females; maximum carapace width 2.5 (1.6–2.9) in males, 5.3 (2.3–9.5) in females. Carapace posterior sinus length 0.7 (0.5–1) in males, 2.5 (0.5–5, n = 22) in females; width 0.6 (0.3–0.7) in males, 1.6 (0.5–4.2, n = 22) in females. Cephalothorax length 1.8 (1.3–2.1) in males, 2.6 (1.6–5.1, n = 22) in females; anterior width 1.6 (1.1–1.9) in males, 3 (1.7–7) in females. Abdomen length 0.7 (0.6–1.3) in males, 0.6 (0.3–0.8) in females; width 0.6 (0.3–0.8) in males, 0.7 (0.3–2.1) in females. Abdomen posterior sinus length 0.06 (0.05–0.1) in males, 0.09 (0.04–0.2) in females; width 0.04 (0.4–0.6, n = 5) in males, 0.08 (0.03–0.3, n = 25). Eyes diameter (µm) 103.3 (65.8–103.4) left and 109 (65.8–125) right in male, 197 (125–300, n = 19) left and 187.5 (150–275, n = 19) right in female; transverse distance between eyes (µm) 483 (310.2–601.7) in male, 955 (498.2–1975, n = 19) in female. First maxillae outer diameter (µm) 705 (367–1025) left and 672 (320–975) right in males, 1034 (545–1500) left and 1016 (525–1500) right in females; inner diameter 522 (235–750) left and 498 (235–675) right in males, 747 (414–1275) left and 719 (291–1150) right in females. Number of support rods in suction cups 39–52 in males and 45–59 in females; number of sclerites per support rod 2 in males and 2 in females. Remarks. Argulus pestifer is easily diagnosed by the presence of 3 pairs of frontal chitinous bars, the median an inverted Y-like shape, in the cephalothorax (Ringuelet 1948) (Fig. 9H). Moreover, the carapace alae that in males covers all four legs and in females just passes the third legs; the absence of spines on the ventral side of the carapace; and the three pairs of spatulate spines on the basal plate of the second maxillae (Figs. 9A, G) (Ringuelet 1948), allow identification of this species. In the present paper, we noted some characteristics to be added to the diagnosis of this species. Spine like and multi-digit scales are present in the second maxillae and the legs, but were not observed in the thorax. The flagellum observed in the first two pairs of legs in females was only in the first legs of males. Despite the fact that Ringuelet (1948) does not mention the number of segments of the first and second antenna his drawings reflected our findings, with the first antenna 4-segmented and the second antenna 5-segmented (Figs. 9C, H). In the first segment of the second antennae of the females we observed a sensilla and a stout seta (Figs. 9C–D). The morphology of the fifth segment of the second maxillae of this species is quite like others species of Argulus, with two hooks resembling claws or chelae and a dorsal structure that resembles a shield (Fig. 9F). The absence or subdevelopment of morphological structures in argulids has been documented (Avenant- Oldewage & Knight 1994; Møller & Olesen 2010; Ringuelet 1943, 1948) with some representing a secondary loss, such as the absence of a pre-oral spine in specimens of Chonopeltis (Møller & Olesen 2010). The absence of a preoral stylet in males and females of A. pestifer was unambiguously confirmed in the present study (Figs. 9A–B, G– H). The absence of postantennal spines in A. pestifer, as reported by Ringuelet (1948) may be unique among Argulus species from Neotropical Region. In his key, Wilson (1944) referred to Argulus rotundus Wilson, 1944, as an Argulus species without postantennal spines. However, in his description Wilson (1944) said nothing about this structure, although he drew a sketch of one in the plate under number 118.

Published as part of Tavares, Luiz E. R., 2017, A new species of Argulus (Crustacea, Branchiura, Argulidae) from the skin of catfish, with new records of branchiurans from wild fish in the Brazilian Pantanal wetland, pp. 447-469 in Zootaxa 4320 (3) on pages 460-462, DOI: 10.11646/zootaxa.4320.3.3, http://zenodo.org/record/893754