Demidospermus takemotoi Justo, Martins & Cohen, 2024, sp. nov.

Demidospermus takemotoi sp. nov. (Figs. 3 A–G) Type-host: Ageneiosus inermis (Linnaeus, 1766) Site of infestation: Gills Type-locality: Juruá River, Acre, Brazil (7º40’34.1’’S, 72º39’39.5”W). Parasitological indexes: Total number of hosts: 5, Number of infested hosts: 1; total number of parasites: 5. Specimens deposited: Holotype (CHIOC 40449 a), Paratypes (CHIOC: 40449 b –F; 40450) Etymology: The specific name is in honor of Dr Ricardo Massato Takemoto for his contributions to the knowledge of neotropical fish parasites. Description (Based on five specimens mounted in Hoyer’s medium). Body elongated, fusiform, 825–1,100 (937; n=5) long by 155–325 (216; n=5) maximum width. Pharynx 57–60 long by 51–62 wide (n=2). Male copulatory organ tubular, long, proximally wider, turns back on itself near the base in most specimens, tapering, with a thin projection at subdistal region, 114–145 (130; n=4); Accessory piece long, tubular, slender, 100–140 (130; n=4) (Fig. 3A). Gonads in tandem; vas deferens looping left intestinal caecum. Seminal vesicle fusiform. Vagina sclerotized, funnel-shaped sinistral opening (Fig. 3B). Germarium pretesticular. Oviduct, ootype, and uterus not observed. Vitelline follicles scattered throughout the trunk, not overlapping the reproductive organs. Haptor 112–200 (n=3) wide. Ventral bar W-shaped 52–65 (60; n=4) long (Fig. 3C); dorsal bar slightly straight to V-shaped 33–62 (53; n=5) long (Fig. 3D, E). Ventral anchor with elongated and pointed superficial root; deep root round and long; short shaft, long point, 29–37 (32; n=10), base 18–28 (22; n=10) (Fig. 3F). Dorsal anchor with well-developed superficial root distally pointed; deep root well defined, rounded; short shaft and long point 31–35 (32; n=10), base 20–25 (23; n=9) (Fig. 3G). Hooks dissimilar in shape and similar in size, 17–22 (19; n=24). Hook pairs 1–4 and 6–7 equal, with recurved point, straight shaft, erected thumb and delicate shank, and curved proximal subunit; FH loop about shank length (Fig. 3H). Hook pair 5 slightly recurved point, delicate shaft, protruding thumb and expanded shank (Fig. 3I). Remarks: Demidospermus takemotoi sp. nov. resembles D. annulus by the shape of MCO, but differs by the morphology of the accessory piece, where that of D. annulus is straight to slightly curved, rod-shaped, with only a distal end in contact with MCO. In contrast, in the new species, the accessory piece is long, tubular, slender, and almost the same size as the MCO. The new species also resembles Demidospermus mortenthaleri Mendoza-Palmero, Scholz, Mendoza-Franco & Kuchta, 2012 by the shape of the bars and by the MCO as a slender tube with an irregular base, forming a counterclockwise loop at its mid region. The new species differs from it in the morphology of the accessory piece, where that of D. mortenthaleri is L-shaped with groove along its length, serving as a guide of the MCO distally, and in the new species is a long and slender tube.