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

Demidospermus bifurcatus sp. nov. (Figs. 2 A–G) Type-host: Ageneiosus inermis (Linnaeus) Site of infestation: Gills Type-locality: Moa River, Acre, Brazil (7º35’28.3’’ S, 73º55’17.4” W). Parasitological indexes: Total number of hosts: 1; number of infested hosts: 1; total number of parasites: 10. Specimens deposited: Holotype (CHIOC 40448 a), Paratypes (CHIOC: 40448 b–g) Etymology: The specific name is a Latin adjective (bifurcatus = forked), due to the bifurcation in the distal portion of the MCO. Description (Based on 9 specimens mounted in Hoyer’s medium). Body elongated, fusiform, 355–650 (537; n=8) long by 78–175 (126; n=8) wide at the level of the ovary. Cephalic region broad; cephalic lobes weakly developed, 3 bilateral pairs of head organs; cephalic glands indistinct. Subspherical eyespot granules scattered throughout cephalic region. Pharynx subspherical to spherical 40–62 (54; n=8) long by 28–57 (49; n=8); esophagus short, intestinal ceca confluent posterior to gonads. Male copulatory organ robust tube, inverted C-shaped, with a bisected tip at its distal end, irregular base, 69–111 (88; n=8); accessory piece robust, embracing the MCO in its full extension, 63–105 (79; n=8), proximal portion expanded forming two arms, one wider than the other, with a tendency to wrap around the base of the MCO (Fig. 2A). Gonads in tandem; testis 187 (n=1) long; vas deferens looping left intestinal cecum. Seminal vesicle long, fusiform. Germarium pretesticular 75 (n=1) long. Slightly sclerotized vagina with bifurcated canal and ornate opening (Fig. 2B). Oviduct, ootype, and uterus not observed. Vitelline follicles densely distributed in trunk, not overlapping the reproductive organs. Peduncle inconspicuous. Haptor width similar to the body. Haptor sub-hexagonal, 71–215 (116; n= 8) wide. Ventral bar slightly curved 42–59 (50; n=8) long (Fig. 2C); dorsal bar open V-shaped 44–59 (52; n=8) long (Figs. 2D). Ventral anchor with elongated superficial root; deep root rounded; straight shank, straight and long point, extending slightly beyond superficial root 28–35 (32; n=16), base 17–24 (19; n=16) (Fig. 2E). Dorsal anchor with well-developed superficial root, deep root rounded, short, straight point extending slightly beyond superficial root, 22–35 (31; n=16), base 16–22 (19; n=16) (Fig. 2F). Hooks similar in shape and size, pair 1, 15–21 (18; n=8), pair 2, 15–21 (19; n=8), pair 3, 15–22 (19; n=7), pair 4, 16–19 (18; n=5), pair 5, 17–22 (20; n=5), pair 6, 17–20 (19; n=4), pair 7, 17–19 (19; n=4), with curved point and delicate shaft, protruding thumb, expanded shank proximally; FH loop approximately ⅔ shank length (Fig. 2G). Remarks: Demidospermus bifurcatus is characterized by a MCO formed by a robust tube, inverted C-shaped, with a distal end presenting a bisected tip and a robust accessory piece, embracing the MCO in its full extension, proximal portion to the base of the MCO expanded forming two arms; this morphology of the copulatory complex distinguishes the new species from all congeners.