Acanthogyrus (Acanthosentis) barbonymi Lisitsyna, Oros, Ribas, Poonlaphdecha & Barčák, 2025, sp. nov.

Acanthogyrus (Acanthosentis) barbonymi sp. nov. Figs 1, 2, 3 Type host. Tinfoil barb Barbonymus schwanenfeldii (Bleeker) (Cypriniformes, Cyprinidae). Type locality. Nong Khai Inland Fisheries Research and Development Center, Had Sai Thong village, Nong Khai province, Thailand (17°55.318'N, 102°36.230'E). Site of infection. Intestine. Infection rates. Prevalence 87.0 %, intensity 7–67. Type material. Deposited in the Helminthological collections of IPCAS and NHMUK (Coll. nos. IPCAS A-145 and NHMUK 2025.1.8.1-15). Molecular data. The sequences of nuclear 18 S rRNA (1,767 bp), 28 S rRNA (1,188 bp) and the mitochondrial COI (657 bp) genes of Acanthogyrus (Acanthosentis) barbonymi sp. nov. were deposited in the GenBank database (Acc. nos. PQ 636375 – PQ 636378, PQ 636383 – PQ 636385, PQ 631040, PQ 631041). Etymology. Species name is derived from the scientific name of the host. Morphology. Quadrigyridae with features of genus Acanthogyrus and subgenus Acanthosentis. Acanthocephalans white in color, medium size, usually sickle-shaped, with maximum width in anterior third of body (Figs 1 – 3). Female larger than male. Anterior body part with two fields of tegumental spines in rings with rosette-shaped root processes (Figs 1 B, 2 A, D, E). Number of giant tegumental nuclei not constant. Proboscis small, round, armed with 18 hooks in three rows, six hooks in each row. Sensory pore in base of proboscis (Figs 1 A, B, 3 B). Hooks of the anterior row large, with simple massive roots directed posteriorly, located irregularly, three slightly anteriorly, three slightly posteriorly (Fig. 1 D). Hooks of middle row twice as small as hooks of anterior row, with complex forked roots directed anteriorly. Hooks of basal row smallest, with simple roots directed posteriorly (Fig. 1 A, D). Neck conical. Proboscis receptacle with single-layer muscular wall, with cephalic ganglion at bottom. Lemnisci almost equal in length, extending to middle of body. Genital pore terminal in both sexes (Figs 1, 2 B, C, 3 D). Male (based on nine mature specimens with sperm, measurements of the holotype specimens followed with measurements of type series). Trunk 3.54 (2.78–4.93) mm long, 618 (585–921) wide (Fig. 1 B). Tegumental spines of anterior field with nine (9–12) rings, 16 (16–20) spines in each ring. Posterior rings of anterior field incomplete dorsally, basal ring with 2–10 spines. Length of spine blades 13 (12–16), diameter of rosette root 15 (12–16). Distance between spines fields (154–189). Somatic spines of posterior field with nine (8–10) rings, 12 (12–15) spines in each ring. Posterior rings of posterior spines field incomplete dorsally, basal ring with five or six spines. Length of spine blades 7 (7–14), diameter of rosette root 14 (12–24). Body wall with six (5–7) giant tegumental nuclei, four (2–4) dorsal, and two (1–3) ventral. Proboscis 73 (73–99) × 108 (108–138). Length of hook blades of anterior row 62–63 (51–69), middle 26 (21–26), basal 18 (18–24). Length of hook roots of anterior row 26–28 (25–45), middle 19 (16–20), basal 10 (10–15). Neck 74 (72–110) long, wide in anterior part 86 (86–105), in posterior part 126 (126–163). Proboscis receptacle 424 (370–467) × 91 (91–155). Lemnisci do not reach anterior testis, 874 (483–1,499) × 71 (44–92) and 834 (473–1,561) × 76 (44–98). Organs of reproductive system in posterior half of body. Testes oval, in tandem, anterior larger than posterior. Anterior testis 620 (429–1,078) × 399 (313–605), posterior testis 477 (378–702) × 356 (221–590). Cement gland oval, adjacent to posterior edge of posterior testis, 339 (267–575) × 302 (261–628). Almost round cement reservoir posteriorly to cement gland, 171 (121–280) × 179 (153–312). Saefftigen’s pouch club-shaped, 249 (432–621) × 82 (82–173). Vas deferens elongated, 393 (393–474) × 124 (119–124). Type specimen with leaf-shaped penis 94 × 42. Evaginated bursa 361 (335–361) × 229 (229–343). Female (based on 13 specimens, 7 with eggs, 6 without eggs). Trunk 5.60–11.72 mm long, 0.86–1.45 mm wide. At base of caudal process 4–8 very small spines in one ring (Fig. 3 E). Tegumental spines of anterior field with 10 or 11 rings, 16–22 spines in each ring. Posterior rings of anterior field incomplete dorsally, basal ring with 8–11 spines. Length of spine blades 12–15, diameter of rosette root 15–20. Distance between spines fields 100–262. Somatic spines of posterior field with 10–12 rings, 13–17 spines in each ring. Number of spines in ring decreases towards basal ring to 3–12. Length of spine blades 10–13, diameter of rosette root 13–20. Body wall with 6–10 giant tegumental nuclei, 2–6 dorsal, 2–5 ventral. Proboscis 112–136 × 133–170 (Figs 1 A, 3 C). Length of hook blades of anterior row 59–78, middle 28–34, basal 26–27. Length of hook roots of anterior row 33–45, middle 18–31, basal 15–17. Neck 42–129 long, width of anterior part 105–124, width of posterior part 166–320. Proboscis receptacle 361–560 × 124–147. Lemnisci 1.29–1.54 mm long, 83–154 wide. Female reproductive tract in posterior part of body, 962–1,400 long. Vagina with two sphincters (Fig. 1 C, E). Eggs fusiform, elongate, no polar prolongation of fertilization membrane, 21–24 × 8–10 (Fig. 2 F). Posterior end of female forms somewhat pronounced dome-shaped process, 180–343 × 198–356 (Fig. 3 D) with complete or incomplete ring of 4–8 small spines at its base. At the moment of copulation, the male’s bursa embraces the dome-shaped caudal process of the female (Fig. 2 C), and the eggs are injected into the cavity of the male bursa. After copulation, the bursa invaginates and some of the eggs may temporarily remain in cavity of bursa (Fig. 2 B). Remarks. To date, 57 species have been described in the subgenus Acanthosentis of the genus Acanthogyrus, mainly parasites of freshwater fish in South and Southeast Asia (Amin 2005, 2013; Naidu 2012; Saxena et al. 2013; Amin et al. 2017; Mohd-Agos et al. 2021; Rana and Kaur 2023). Acanthogyrus (Acanthosentis) barbonymi sp. nov. differs from most species of the subgenus in the arrangement of rings of tegumental spines in two fields with a more or less pronounced distance between them, as well as the presence of a dome-shaped process with a ring of tiny spines at the base at the posterior end of the females. The arrangement of spines in two fields is characteristic for two species of the subgenus Acanthosentis, A. (A.) multispinus (Wang, 1966), described from the silver carp Hypophthalmichthys molitrix (Valenciennes) from China (Wang 1966) and A. (A.) bispinosa Rana & Kaur, 2023 from the mrigal carp Cirrhinus mrigala Hamilton and the orangefin labeo Labeo calbasu Hamilton in Malaysia. However, A. (A.) barbonymi sp. nov. differs from A. (A.) multispinus in two characteristics: i) posterior rings of tegumental spines of A. (A.) barbonymi sp. nov. are incomplete in both fields, and the rings of the posterior field do not extend to the middle of the body; while the rings of spines in both fields of A. (A.) multispinus are complete and the rings of the posterior field of spines reach the posterior end of the body; ii) the proboscis hooks of the middle row A. (A.) barbonymi sp. nov. are half the size of the hooks of the apical row; while in A. (A.) multispinus, the size of the proboscis hooks gradually decreases from the apical to the basal row. A. (A.) barbonymi sp. nov. differs from A. (A.) bispinosa in the number of rings of spines, with 9–12 rings of spines in the anterior field, 8–11 rings of spines in the posterior field versus 7–10 rings of anterior spines and 23–38 rings of posterior spines in A. (A.) bispinosa (Rana and Kaur 2023). One species of the subgenus Acanthosentis, A. (A.) siamensis (Farooqi & Sirikanchana, 1987) Amin, 2005, has been found in the silver barb Barbonymus gonionotus (Bleeker) (= Puntius gonionotus) in Thailand (Farooqi and Sirikanchana 1987). Acanthogyrus (A.) barbonymi sp. nov. and A. (A.) siamensis have similarities in the size of the proboscis hooks and the shape of the female caudal process; however, they differ in the number of rings of body spines: 20–26 in A. (A.) barbonymi sp. nov. vs 3–4 in A. (A.) siamensis. Recently, Mohd-Agos et al. (2021) described three new species of the subgenus Acanthosentis from Barbonymus schwanenfeldii from Lake Kenyir in Malaysia, namely A. (A.) kenyirensis Mohd-Agos, Mohd-Husin, Zakariah, Yusoff, Wahab, Jones, Hassan, 2021, A. (A.) tembatensis Mohd-Agos, Mohd-Husin, Zakariah, Yusoff, Wahab, Jones, Hassan, 2021 and A. (A.) terengganuensis Mohd-Agos, Mohd-Husin, Zakariah, Yusoff, Wahab, Jones, Hassan, 2021. Although described from the same fish host, A. (A.) barbonymi sp. nov. differs from these three species in the size of the proboscis hooks, and the hooks of the middle and basal rows of A. (A.) barbonymi sp. nov. have similar lengths and are approximately half as long as the hooks of the anterior row, whereas in A. (A.) kenyirensis, A. (A.) tembatensis, and A. (A.) terengganuensis the hooks of the anterior and middle rows are of comparable length and more than twice as long as the hooks of the basal row. Additionally, A. (A.) barbonymi sp. nov. clearly differs from them in other morphological characters: i) A. (A.) barbonymi sp. nov. has 4–11 giant nuclei in the tegument whereas A. (A.) kenyirensis and A. (A.) terengganuensis have no giant nuclei in the tegument; ii) the tegumental spines of A. (A.) barbonymi sp. nov. form two fields, with 9–12 rings of spines in the anterior field and 8–11 rings of spines in the posterior field whereas tegumental spines in A. (A.) kenyirensis and A. (A.) tembatensis are in one field with eight or nine rings; iii) A. (A.) kenyirensis, A. (A.) tembatensis, and A. (A.) terengganuensis have a unique collar ring on the neck and a muscular-like structure on both sides of proboscis attached to the ring whereas this structure absent in A. (A.) barbonymi sp. nov.; iv) females of A. (A.) barbonymi sp. nov. have a caudal process with tiny spines in one ring at its base wher