Urocleidoides indianensis n. sp.

(Fig. 3A–K; 2A–C)

Type host. Parodon nasus Kner (Characiformes: Parodontidae).

Site of infestation. Gills.

Type locality. Indiana stream (Capivara River, Tietê River, Upper Paraná River basin), municipality of Botucatu, São Paulo State, Brazil (22°53’57.4’’S, 48°23’11.3’’W).

Infestation rate. Prevalence 85%; minimum mean intensity of infestation 6 ± 1.8 (1–34); minimum mean abundance 5.9 ± 1.6 (0–34).

Specimens deposited. Holotype (CHIOC 39712 a); 6 paratypes CHIOC (39712b–e; 39713 a–b); 8 paratypes INPA (841a–h).

Representative DNA sequence. 1,251 bp long of partial sequence of the 28S rDNA (D1–D3 region). Genbank accession number OK482868; paragenophore INPA (841i).

Etymology. The specific name relates to the water body (Indiana stream) where the hosts were collected.

Description. Based on 16 specimens fixed in Gray and Wess’ medium and 2 stained with Gomori’s trichrome: Body fusiform 628–789 (711; n = 9) long; greatest width 107–149 (136; n = 9) near mid-length. Cephalic lobes poorly developed; 3 bilateral pairs of head organs. Few subspherical granules scattered from cephalic lobes to level of male copulatory organ present or absent. Pharynx spherical, 27–35 (31; n = 3) long, 28–35 (31; n = 3) wide; esophagus moderately long; intestinal ceca confluent posterior to testis. Peduncle short; haptor subhexagonal, 106–145 (119; n = 9) long, 88–143 (112; n = 9) wide. Ventral anchor 29–31 (30; n = 16) long, base 14–18 (16; n = 16) wide; well-developed roots, deep root conspicuous, rounded end, elongate superficial root, groove at base, shaft long evenly curved, elongate point not exceeding base width; anchor filament double (Fig. 3B). Dorsal anchor 22–25 (24; n = 16) long, base 10–13 (12; n = 16); moderately developed roots, deep root short, superficial root slightly longer, shaft long evenly curved, elongate point slightly exceeding base width, anchor filament double (Fig. 3E). Ventral bar 25–34 (29; n = 16) long, bowed, with noticeable expanded ends (Fig. 3C). Dorsal bar 29–35 (32; n = 16) long, open V-shaped, with rounded ends and conspicuous medial projection on posterior margin present (Fig. 3D). Hooks with protruding thumb, delicate shaft and point, point slightly curved, dilated shank with two subunits (Figs. 3F–I). Hook pairs 1 (Fig. 3H) and 7 (Fig. 3G) similar in size, 16–18 (17; n = 16) long, filamentous hooklet (FH) loop about 1/3 of shank length, union of shank subunits at half of shank length in pair 1, and at second third of shank length in pair 6. Hook pairs 2, 3, 4, and 6 (Fig. 3I) similar 20–23 (22; n = 16) long, FH loop about ¼ of shank length, union of shank subunits at the first third portion of shank length. Hook pair 5 (Fig. 3F) smallest in size 12–14 (13; n = 16) long, FH loop about ½ of shank length, union of shank subunits at the second third of shank length. MCO not articulated to accessory piece; MCO 27–40 (36; n = 13) long, a coiled thin delicate tube of about 4 ½ counterclockwise rings having broad base surrounded by sheath-like sclerotizations (Fig. 3K; 2A). Accessory piece 20–27 (22; n = 16) long, 16–22 (19; n = 16) wide, bulb-shaped (Fig. 3K; Fig. 2A). Gonads overlapping. Testis dorsal to ovary, slightly visible at posterior end of germarium; seminal vesicle a dilation of vas deferens; prostatic reservoir not observed. Vas deferens looping left intestinal caecum. Germarium 26 long, 10 wide; oviduct, ootype, uterus, and egg not observed. Vaginal aperture sinistrolateral, vaginal tube weakly sclerotized, convoluted, emptying seminal receptacle (Figs. 3J; 2B). Vaginal sclerite 22–36 (28; n = 16) long, robust, sickle-shaped, distally forked associated with sclerites from the vaginal tube (Figs. 3J; 2B). Vitelline follicles scattered throughout trunk, except in regions of reproductive organs.

Remarks. The new species is placed in Urocleidoides due to the presence of the characteristics stated in the amended diagnosis of the genus proposed by Kritsky et al. (1986) and Zago et al. (2020), i.e., coiled MCO with counterclockwise rings, vaginal sclerite present, overlapping gonads, hooks with dilated shanks, hook pairs 1 and 5 reduced in size. Urocleidoides indianensis n. sp. differs from its congeners mainly by the morphology of the vaginal sclerite that is robust, sickle-shaped, forked at the distal end associated with sclerites from the vaginal tube (Figs. 3J; 2B). Moreover, the bulb-shaped accessory piece of the male copulatory complex in the new species is very unique among all congeners (Figs. 3K; 2A). Urocleidoides xinguensis Moreira, Scholz & Luque, 2015 presents vagina sclerite resembling a sickle in shape and forked at the distal end, but differs from the new species by the morphology of the ventral/dorsal anchors, dorsal bar lacking medial projection, hooks of same size, MCO with 2½ counterclockwise rings, and accessory piece long, grooved and distally bent (Moreira et al. 2015). Urocleidoides tocantinensis Freitas, Bezerra, Meneses, Justo, Viana, Cohen, 2021 also presents vagina sclerite forked, but differs from the new species by the morphology of the ventral/dorsal anchors and bars, accessory piece, and MCO as a straight tube (Freitas et al. 2021). Urocleidoides cultellus Mendoza-Franco & Reina, 2008; U. flegomai Mendoza-Franco, Aguirre-Macedo & Vidal-Martínez, 2007; U. neotropicalis Mendoza-Franco & Reina, 2008; and U. simonae Mendoza-Franco, Caspeta-Mandujano, Salgado-Maldonado & Matamoros, 2015, also present MCO as a thin delicate coiled tube with four or more counterclockwise rings (~5, 4 ½, 5 ½, 4 to 5, respectively) and a broad base with sclerotized ornamentation. However, the male copulatory complex of new species can be differentiated from the above-mentioned species [see Mendoza-Franco & Reina (2008); Mendoza-Franco et al. (2007; 2015), for details] by its unique shape of the accessory piece (bulb-shaped). Urocleidoides indianensis n. sp. is the third species of the genus described from a parodontid host (P. nasus). Urocleidoides neotropicalis was described from the gills of Saccodon dariensis Meek & Hildebrand in Panama (Mendoza-Franco & Reina, 2008), and U. tenuis was described from the gills of A. piracicabae in Brazil (Zago et al. 2020). The three species from parodontids share morphological similarities of bars—ventral bar with noticeable expanded ends, and dorsal bar with the presence of a conspicuous medial projection on posterior margin. Nevertheless, Urocleidoides indianensis n. sp. can be differentiated from U. neotropicalis and U. tenuis by the morphology of the anchors, vaginal sclerite, and male copulatory complex (accessory piece and MCO).