D. N. D. Bahanak 1, 2, J. Nack 3, A. R. Bitja Nyom 4, A. Pariselle 5*, C. F. Bilong Bilong 1

Vie et milieu - Life and environment, 2017, 67 (2): 81-89 Quadriacanthus spp. (Monogenea, Dactylogyridea) from Heterobranchus longifilis (Teleostei, Clariidae) in the River Boumba (Congo Basin: Cameroon) with the description of three new species D. N. D. Bahanak 1, 2, J. Nack 3, A. R. Bitja Nyom 4, A. Pariselle 5*, C. F. Bilong Bilong 1 1 University of Yaoundé 1, Faculty of Science PO Box, 812 Yaoundé, Cameroon 2 IRAD, B.P. 2123, Yaoundé, Cameroon 3 University of Douala, Faculty of Sciences, PO Box 24157, Douala, Cameroon 4 University of Ngaoundéré, Faculty of Science, PO Box 454, Ngaoundéré, Cameroon 5 Institut des Sciences de l Évolution de Montpellier, IRD, BP 1857, Yaoundé, Cameroon * Corresponding author: antoine.pariselle@ird.fr CATFISH CLARIIDAE DACTYLOGYRIDAE QUADRIACANTHUS longifilisi QUADRIACANTHUS THYSI QUADRIACANTHUS TRICORNICULAI QUADRIACANTHUS TRIUNGUISI QUADRIACANTHUS NDOUBAI PARASITE RICHNESS AFRICA ABSTRACT. Twelve specimens of Heterobranchus longifilis sampled from the River Boumba were examined for their monogenean gill parasites. Quadriacanthus longifilisi N Douba, Lambert & Euzet 1999 and Q. thysi N Douba, Lambert & Euzet 1999 are newly recorded in the studied locality. Three new species have also been described: Q. tricorniculai n. sp., Q. triunguisi n. sp., and Q. ndoubai n. sp. Quadriacanthus tricorniculai and Q. triunguisi are characterized by the unique morphology of their accessory pieces, which end in a three-head hydrashaped structure, with tentacles being longer in Q. tricorniculai; proximal extremity of accessory piece is stronger for Q. triunguisi, while Q. ndoubai is distinguished by the size of its male copulatory organ (larger than 80 μm) and the fork shaped distal extremity of the accessory piece of the male copulatory complex. The variability of monogenean species richness of Heterobranchus longifilis between Ivory Coast and Cameroon is discussed. INTRODUCTION Heterobranchus Geoffroy Saint-Hilaire, 1809, originating from Africa, is a teleost genus characterized by species having a large adipose fin, located between the rayed dorsal and the caudal fins; both fin rays are supported by elongate neural spines. The head is depressed, flattened, and the lateral bones are in contact. The eyes are small and have free borders. Four species are known: H. longifilis Valenciennes, 1840, H. bidorsalis Geoffroy Saint- Hilaire, 1809, H. isopterus Bleeker, 1863 and H. boulengeri Pellegrin, 1922 (Teugels et al. 1990, Stiassny et al. 2007). Heterobranchus longifilis has been introduced worldwide (within Africa, Asia and America, etc.) for the purpose of aquaculture, because of its favorable characteristics: a robust body, an omnivorous diet, the capacity to live in hypoxic conditions, a high fecundity, a continuous reproduction, and a high growth rate [10 g per day, one of the fastest observed amongst African fish species tested in aquaculture (Legendre et al. 1992)]. These characteristics make H. longifilis (and Heterobranchus spp. in general) of great value for aquaculture (Legendre et al. 1992), which nevertheless can be impaired by pathology due to parasites. For example, monogeneans may contribute to significant losses in aquaculture (Komarudin et al. 1992, Bilong Bilong et al. 1998); therefore, a prerequisite for successful aquaculture practice is the prevention of disease outbreaks and mass development of pathogenic infections (Obiekezie & Ekanem 1995). Several studies have been conducted on monogenean parasites of African Clariidae (Paperna 1961, 1969, 1973, 1979, Ergens 1973, 1988, Molnar & Mossalam 1985, Birgi 1988, Kritsky & Kulo 1988, Kritsky 1990, Douëllou & Chishawa 1995, N Douba et al. 1999, N Douba & Lambert 2001, Nack et al. 2005, 2010, Bilong Bilong et al. 2007, Barson et al. 2008, 2010, etc.), but among them only two concerned Heterobranchus spp. (Kritsky & Kulo 1988, N Douba et al. 1999) and none was undertaken in the Congo Basin. The present study was carried out in the River Boumba, at Zoulabot situated in the Congo Rainforest (East Region, Cameroon). River Boumba originates from the Haut Nyong division (780 m a.s.l.) at the point of contact with the springs of River Nyong which is a swampy area (Olivry 1986) (Fig. 1). MATERIALS AND METHODS Collection and examination of fish hosts and monogeneans: Specimens (n = 12) of Heterobranchus longifilis examined in this study were caught in River Boumba at Zoulabot (3 18 42.89 N, 14 04 43.19 E, Congo Basin, Cameroon) using gill nets, cast nets, fish-traps or hook lines. Fish were dissected immediately in the field or placed immediately at 15 C in a portable Engel

82 D. N. D. BAHANAK, J. NACK, A. BITJA NYOM, A. PARISELLE, C. F. BILONG BILONG Fig 1. Localization of the studied area. Fig 2. Morphometrics of Quadriacanthus spp. used in this study are based on Gussev (1962) modified by N Douba et al. (1999). DA, Dorsal Anchor: (a) length, (ab) base width, (e) point length; MCC, Male Copulatory Complex: MCO, Male Copulatory Organ, Ap, Accessory piece length; DC, Dorsal cuneus: (j) length, (i) width; VC, Ventral cuneus: (j) length; DB, Dorsal Bar: (ct) center length, (h) median process length, (w) width, (x) length; H, Hooks length; VB, Ventral Bar: (w) width, (x) length; Vg, Vagina. deep-freezer, transported to the laboratory and stored at 21 C. After thawing, gill arches were isolated from mouth cavity by dorsal and ventral sections, placed in a Petridish containing tap water. The parasites were dislodged from the gill filaments with a needle. The monogeneans were fixed between slide and cover slip in a drop of Malmberg mixture (glycerin ammonium picrate). The preparation was then sealed using Glyceel [made after Bates (1997)]. From these preparations, the identification, based on morphology and size of sclerotized pieces of haptor and copulatory complex, was done referring to Kritsky & Kulo (1988) and N Douba et al. (1999). Authors of the new taxa are different from the authors of this paper: Article 50.1 and Recommendation 50A of the International Code of Zoological Nomenclature. Type material and vouchers are deposited in the helminth collection of the Royal Museum for Central Africa (MRAC) Tervuren (Belgium). Morphometry: The measurements and drawings of the sclerotized pieces of the haptor and copulatory complex were made with the aid of a Leica microscope DM 2500, LAS software (3.8) and Corel Draw X4 software (ver 14.0.0.701; Corel Corporation, www.corel.com/). These measurements and the numbering of haptoral pieces were carried out following Gussev (1962) modified by N Douba et al. 1999) (Fig. 2); measurements are given in micrometers as follows: mean (minimum maximum). RESULTS Five different monogenean species were identified during this study, all dactylogyrid parasites, with anatomy corresponding to the diagnosis of Quadriacanthus used by Bahanak et al. (2016). Quadriacanthus longifilisi N Douba, Lambert & Euzet 1999 (Fig. 3) Type host: Heterobranchus longifilis Valenciennes, 1840. Site: gill filaments. Type locality: River Agnéby, Ivory Coast. New Locality: Zoulabot, River Boumba, East Cameroon Region (3 18 42.89 N, 14 04 43.19 E). Voucher specimens: MRAC No.38177 and No.38178. Materials studied: 27. Prevalence: 100 %.

NEW SPECIES OF QUADRIACANTHUS FROM THE CONGO BASIN IN CAMEROON 83 Fig 3. Quadriacanthus longifilisi. MCC, Male Copulatory Complex; Vg, Vagina; DB, Dorsal Bar; DA, Dorsal Anchor; DC, Dorsal Cuneus; VB, Ventral Bar; VA, Ventral Anchor; VC, Ventral Cuneus; I-VII, Hooks. Scale bar = 20 μm. Fig 4. Quadriacanthus thysi. MCC, Male Copulatory Complex; DB: Dorsal Bar; DA, Dorsal Anchor; DC, Dorsal Cuneus; VB Ventral Bar; VA, Ventral Anchor; VC, Ventral Cuneus; I-VII, Hooks. Scale bar = 20 μm.

84 D. N. D. BAHANAK, J. NACK, A. BITJA NYOM, A. PARISELLE, C. F. BILONG BILONG Table I. Original and newly obtained measurements of Quadriacanthus longifilisi and Q. thysi. Legend: Ph, pharynx; L, total body length; l, body width; MCO, Male Copulatory Complex; AP, Accessory Piece; I-VII, hooks length; DB, Dorsal Bar: (x) length, (w) width, (h) median process length, (ct) center length; DA, Dorsal Anchor: (a) length, (ab) base diameter, (e) point length; DC, Dorsal Cuneus: (i) width, (j) length; VB, Ventral Bar: (x) length, (w) width; VA, Ventral Anchor: (a) length, (ab) base diameter, (e) point length; VC: (j) Ventral Cuneus length. * Measurements from the original description of Quadriacanthus longifilisi and Q. thysi, by N Douba et al. (1999). Q. longifilisi Q. longifilisi* Q. thysi* Q. thysi Ph 40 (32-45) 37 (30-40) 42 (35-50) 33 L 522 (300-853) 580 (470-795) 748 (540-820) 735 l 154 (88-176) 138 (100-185) 148 (130-165) 216 MCO 43 (38-47) 39 (35-42) 52 (49-56) 52 AP 41 (33-44) 40 (38-43) 60 (54-65) 60 Vg 24 (20-29) 13 (10-15) I 20 (16-21) 21 (18-23) 18 (17-19) 18 II 14 (13-15) 15 (14-17) 16 (15-17) 16 III 26 (22-28) 27 (24-29) 43 (40-45) 43 IV 37 (35-41) 37 (33-41) 62 (55-66) 62 V 14 (13-15) 16 (15-17) 16 (14-18) 16 VI 14 (13-15) 16 (15-17) 16 (15-17) 16 VII 13 (12-15) 15 (13-17) 15 (14-17) 15 DB x 38 (36-40) 39 (33-43) 51 (48-54) 51 w 16 (14-18) 17 (14-20) 15 (13-18) 15 h 16 (14-20) 18 (15-21) 44 (35-50) 44 ct 33 (30-38) 36 (32-42) 32 (27-37) 32 DA a 50 (48-53) 48 (42-55) 68 (63-72) 68 ab 15 (13-17) 15 (13-17) 18 (17-19) 18 e (4-5) 7 (5-8) 7 (6-8) 7 DC j 21 (18-24) 20 (13-24) 27 (24-31) 27 i 11 (7-12) 11 (7-17) 13 (7-16) 13 VB x 52 (50-56) 54 (50-60) 56 (52-61) 56 w 9 (6-11) 9 (6-11) 8 (7-9) 8 a 38 (36-40) 38 (33-41) 29 (27-31) 29 ab 10 (7-11) 9 (8-11) 8 (7-9) 8 e 15 (12-19) 15 (13-17) 22 (19-24) 22 VC j 15 (13-20) 16 (13-20) 11 (7 17) 11 curved near seminal receptacle and progressively taped near vaginal atrium. Remark: In the original description of Q. longifilisi, N Douba et al. (1999) mentioned some specific features which distinguished this species from other related Quadriacanthus spp. (Q. allobychowskiella Paperna 1979, Q. aegypticus El- Naggar & Serag, 1986 and Q. clariadis Paperna 1961): accessory piece ending with well-developed point vs. delicate one in Q. clariadis, ventral anchor regularly vs. irregularly curved in Q. aegypticus and Q. allobychowskiella. Our observations confirm the presence of these features, except that three processes were found at the distal extremity of the accessory piece instead of two reported in N Douba et al. (1999). However, we consider both parasite populations as belonging to the same species (Q. longifilisi). All measurements of our specimens and those of N Douba et al. (1999) are given in Table I. Quadriacanthus thysi N Douba, Lambert & Euzet 1999 (Fig. 4) Mean abundance: 2.9. Description: Adult worms 522 (300-853) long, 154 (88-176) wide at level of ovary. Pharynx circular 40 (32-45) wide. The dorsal bar with rectangular centre, trapezoidal median process posteriorly directed and with two lateral expansions. Dorsal anchors without handle or guard, with curved blade and short point. Dorsal cunei triangular. Ventral bar V-shaped widely open, showing two medially articulated branches. Ventral anchor with regular curved blade, ending in long point (see Table I). Seven pairs of hooks; pairs IV, III and I (decreasing size) larger than pairs II, V, VI and VII latter pairs about subequal. MCO (Male Copulatory Organ) tubular, taped at distal extremity. Accessory piece straight, showing three distal processes (1 exterior and 2 interior). Tubular vagina wider and Type host: Heterobranchus longifilis Valenciennes, 1840. Site: Gill filaments. Type locality: River Agnéby, Ivory Coast. New locality: Zoulabot, River Boumba, East Cameroon (3 18 42.89 N, 14 04 43.19 E). Voucher specimen: MRAC No.38185. Material studied: 1. Prevalence: 8.3 %. Mean abundance: 0.08. Description: Adult worm 735 long, 216 wide at level of ovary. Pharynx circular 33 wide. Dorsal bar composed of rectangular centre, with large median process posteriorly directed with a tattered end, and two lateral expansions. Dorsal anchor without shaft or handle, but with large and

NEW SPECIES OF QUADRIACANTHUS FROM THE CONGO BASIN IN CAMEROON 85 Fig 5. Quadriacanthus tricorniculai. MCC, Male Copulatory Complex; Vg, Vagina; DB, Dorsal Bar; DA, Dorsal Anchor; DC, Dorsal Cuneus; VB, Ventral Bar; VA, Ventral Anchor; VC, Ventral Cuneus; I-VII, Hooks. Scale bar = 20 μm. Fig 6. Quadriacanthus triunguisi. MCC, Male Copulatory Complex; Vg, Vagina; DB, Dorsal Bar; DA, Dorsal Anchor; DC, Dorsal Cuneus; VB, Ventral Bar; VA, Ventral Anchor; VC, Ventral Cuneus; I-VII, Hooks. Scale bar = 20 μm.

86 D. N. D. BAHANAK, J. NACK, A. BITJA NYOM, A. PARISELLE, C. F. BILONG BILONG curved blade ending with short point of size less or equal to 5 μm (see Table I). Dorsal cuneus triangular. Ventral bar V-shaped with two lateral branches. Ventral anchor smaller than dorsal one but with long point (see Table I). Ventral cuneus Y-shaped. Seven pairs of hooks; pairs IV, III, I (decreasing size) larger than pairs II, V, VI and VII latter pairs about subequal. Vagina not observed. MCC (Male Copulatory Complex) with tubular S-shaped penis, tapering at its distal end, and sigmoid accessory piece, with a C-shaped sclerotized base, ending in hook. Remark: The specimen recovered in the River Boumba differs slightly from the original description by the morphology of its accessory piece showing a C-shaped structure at the basal zone and a small bulk at the distal one. Nevertheless, all the other features considered specific to Q. thysi by N Douba et al. (1999) were observed in our specimen: large dorsal anchors, large dorsal bar median process and S-shaped male copulatory complex with an accessory piece ending with a hook. Therefore, we consider our specimen as belonging to Q. thysi N Douba et al. 1999. Measurements of sclerotized pieces are given in Table I. Quadriacanthus tricorniculai Bahanak, Pariselle & Bilong Bilong n. sp. (Fig. 5) Type host: Heterobranchus longifilis Valenciennes, 1840. Site: Gill filaments. Type locality: Zoulabot, Boumba River, East Cameroon (3 18 42.89 N, 14 04 43.19 E). Type specimens: Holotype: MRAC No. 38186. Paratypes: MRAC No. 38187 and 38188. Materials studied: 6. Prevalence: 40 %. Mean abundance: 0.5. Etymology: the specific name tricorniculai refers to the three tentacles hydra-shaped extremity of the accessory piece. Description: Adult worms 570 (493-707) long, 153 (131-169) wide at level of ovary. Pharynx circular 36 (32-44) wide. Dorsal bar (except for the morphology of the median process), anchor and cunei, ventral bar, anchor and cunei, hook pairs, similar to above species. Tubular MCO tapering at distal end. Accessory piece, tubular at basal extremity, ends in a specific three tentacles hydrashaped extremity. Vagina tubular wide near its junction with seminal receptacle. Remark: This species is easily distinguished from all Quadriacanthus spp. by the unique morphology of the termination of the accessory piece of male copulatory complex. Measurements of sclerotized pieces are given in Table II. Quadriacanthus triunguisi Bahanak, Pariselle & Bilong Bilong n. sp. (Fig. 6) Type host: Heterobranchus longifilis Valenciennes, 1840. Site: Gill filaments. Type locality: Zoulabot, River Boumba, East Cameroon (3 18 42.89 N, 14 04 43.19 E). Type specimens: Holotype: MRAC No. 38183. Paratypes: MRAC No. 38182 and 38184. Materials studied: 4. Prevalence: 30 %. Mean abundance: 0.33. Etymology: the specific name triunguisi refers to the typical three claws-shaped extremity of the accessory piece. Description: Adult worms 1119 (951-1287) long, 235 (166-305) wide at level of ovary. Pharynx diameter 52 (45-59) at widest point. Dorsal bar with rectangular centre, one median process posteriorly directed and two lateral expansions. Dorsal anchor without shaft or handle, but with thick and regular curved blade ending with long point (see Table II). Dorsal cuneus triangular. Ventral bar V-shaped with two lateral branches. Ventral anchor without shaft or handle, but with thin and regular curved blade. Slightly curved ventral cuneus. Seven pairs of hooks; pairs IV, III, I (decreasing size) larger than pairs II, V, VI, VII, latter pairs about subequal. Tubular vagina pear-shaped with thick wall near vaginal aperture. Tubular MCO tapering at the distal end. Accessory piece in form of waved tube, showing stronger skirt-shaped proximal extremity and typical three claws at distal one. Remark: By the morphology of its MCC, this species is close to Q. tricorniculai. Nevertheless, it can be distinguished by: accessory piece tubular, showing stronger skirtshaped proximal extremity and three claws at distal one vs. accessory piece with delicate proximal extremity and opened as three tentacles hydra at distal extremity for Q. tricorniculai; dorsal anchor with thick and robust blade ending with long point (Fig. 6) vs. thin blade ending with short point (Fig. 5) in Q. tricorniculai (a = 48-49 vs. 37-42, ab = 17-18 vs. 12-13, e = 20-22 vs. 3-7); Hook pairs I and III longer in Q. triunguisi than in Q. tricorniculai (I = 21-23 vs. 15-17, III = 22-23 vs. 17-20); Dorsal bar and cunei longer in Q. triunguisi than in Q. tricorniculai (DB: x = 38-47 vs. 31-33, w = 14-25 vs. 11-13), (DC: j = 21-25 vs. 12-17).

NEW SPECIES OF QUADRIACANTHUS FROM THE CONGO BASIN IN CAMEROON 87 Table II. Measurements of new and related studied Quadriacanthus species. Legend: Ph, pharynx; L, total body length; l, body width; MCO, Male Copulatory Complex; AP, Accessory Piece; I-VII, hooks length; DB, Dorsal Bar: (x) length, (w) width, (h) median process length, (ct) center length; DA, Dorsal Anchor: (a) length, (ab) base diameter, (e) point length; DC, Dorsal Cuneus: (i) width, (j) length; VB, Ventral Bar: (x) length, (w) width; VA, Ventral Anchor: (a) length, (ab) base diameter, (e) point length; VC: (j) Ventral Cuneus length. Q. tricorniculai Bahanak, Pariselle & Bilong Bilong Q. triunguisi Bahanak, Pariselle & Bilong Bilong Q. ndoubai Bahanak, Pariselle & Bilong Bilong Q. macrocirrus N Douba, Lambert & Euzet, 1999 Ph 36 (32-44) 52 (45-59) 65 (53-78) 54 (45-70) L 570 (493-707) 1119 (951-1287) 2021 (1068-2591) 754 (605-875) l 153 (131-169) 235 (166-305) 359 (281-504) 199 (170-220) MCO 45 (42-51) 55 (52-59) 91 (86-95) 59 (58-60) AP 55 (45-66) 73 (67-78) 83 (70-91) 64 (62-64) Vg 37 (33-39) (41-42) I 16 (15-17) 22 (21-23) 25 (24-26) 24 (23-25) II 14 (12-16) 16 (15-17) 15 (13-16) 15 (14-16) III 18 (17-20) (22-23) 27 (25-29) 28 (27-30) IV 23 (21-24) (23-24) 40 (37-45) 36 (35-37) V (14-15) (17-18) 16.3 (15-18) 15 (14-16) VI (13-14) (17-18) 16 (15-17) 15 (14-16) VII 14 (12-16) (16-17) 15 (13-16) 14 (13-15) DB x 32 (31-33) 40 (38-47) 45 (44-56) 34 (31-36) w 12 (11-13) 21 (14-25) 24 (21-29) 24 (20-30) h 13 (12-15) 17 (11-21) 28 (22-32) 16 (14-18) ct 26 (24-29) (29-30) 48 (44-56) 34 (30-38) DA a 39 (37-42) (48-49) 60 (56-63) 41 (40-42) ab (12-13) (17-18) 19 (17-22) 15 (12-16) e 5 (3-7) 21 (20-22) 9 (8-10) 7 (6-8) DC j 14 (12-17) 23 (21-25) 33 (29-35) 20 (17-21) i 5 (4-6) 9 (8-11) 9 (7-11) 8 (7-9) VB x 49 (45-51) 51 (49-54) 70 (62-76) 52 (49-54) w 7 (6-9) 11 (10-13) 13 (12-17) 11 (9-12) VA a 36 (33-38) 39 (37-39) 39 (36-41) 32 (31-33) ab 9 (8-11) 11 (10-13) 13 (11-16) e 17 (10-19) 21 (20-22) 12 (10-15) 11 (8-11) VC j 9 (7-11) 10 (9-10) 12 (11-14) 10 (9-11) Quadriacanthus ndoubai Bahanak, Pariselle & Bilong Bilong n. sp. (Fig. 7) Type host: Heterobranchus longifilis Valenciennes, 1840. Site: Gill filaments. Type locality: Zoulabot, Boumba River, East Cameroon (3 18 42.89 N, 14 04 43.19 E). Type specimens: Holotype: MRAC No. 38180. Paratypes: MRAC No. 38179 and 38181. Materials studied: 41. Prevalence: 71 %. Mean abundance: 3.41. Etymology: The name ndoubai is given in honor of Pr V N Douba, Université Houphouët-Boigny (Abidjan, RCI = République de Côte d Ivoire) for his contribution to the knowledge of monogenean parasites of siluriform fishes. Description: Adult worms 2021 (1068-2591) long, 359 (281-504) wide at level of ovary. Pharynx circular 65 (53-78) wide. Dorsal bar with rectangular centre, one median process posteriorly directed and two lateral expansions. Dorsal anchor without shaft or handle, but with curved blade ending with short point (see Table II). Dorsal cuneus triangular. Ventral bar V-shaped with two lateral branches. Ventral anchor without shaft or handle, but with thin and regular curved blade. Y-shaped ventral cuneus. Seven pairs of hooks; pairs IV, III, I (decreasing size) larger than pairs II, V, VI and VII, latter pairs about subequal. MCC with MCO tapered at distal extremity and accessory piece straight, massive with a fork-shaped distal part. Vagina not observed.

88 D. N. D. BAHANAK, J. NACK, A. BITJA NYOM, A. PARISELLE, C. F. BILONG BILONG Fig 7. Quadriacanthus ndoubai. MCC, Male Copulatory Complex; DB, Dorsal Bar; DA, Dorsal Anchor; DC, Dorsal Cuneus; VB, Ventral Bar; VA, Ventral Anchor; VC, Ventral Cuneus; I-VII: Hooks. Scale bar = 20 μm. Remark: This species is close to Quadriacanthus macrocirrus N Douba, Lambert & Euzet 1999 by the massive shape of the ventral and dorsal bars, and the robustness of dorsal anchors. It differs from the latter by the morphology of: the accessory piece (ending by a fork vs. simple extremity), the male copulatory organ (arched in Q. ndoubai vs. straight tube in Q. macrocirrus) and by the size of the MCC: Ap = 70-91 vs. 62-64, MCO = 86-95 vs. 58-60, respectively. Measurement of sclerotized pieces are given in Table II. DISCUSSION The description of three new species of Quadriacanthus in this study doubled the number of those parasitizing H. longifilis. Among these Quadriacanthus species, two (Q. longifilisi and Q. thysi) are known from Agnéby River (Ivory Coast) and now from Boumba River (Cameroon). The presence of both species in such distant countries confirms that fish may migrate between distant river basins, carrying their specific parasitic hitchhikers. The presence on gill filaments of H. longifilis of three parasitic species in Ivory Coast vs. 5 in Cameroon is another evidence of geographic variation of parasite species richness (Norton & Carpenter 1998, Bahanak et al. 2016). This difference may result either from species loss due to bottleneck events, from change of environmental conditions experienced by migrating host populations, or from gain due to lateral transfers or intra-host [synxenic (Euzet & Combes 1980)] speciation (Pariselle et al. 2003, Vanhove et al. 2016). The latter seems to be accredited by the presence of morphological closely related species (e.g. Q. tricorniculai sp. n. and Q. triunguisi sp. n.) on the same H. longifilis individuals (see Tripathi et al. 2007). The slight differences in morphology of MCC of our specimens (Q. longifilisi and Q. thysi) redescribed herein with those studied by N Douba et al. (1999) are probably due to the divergent evolution by vicariance between Cameroonian and Ivoirian host populations. REFERENCES Bahanak DND, Nack J, Pariselle A, Bilong Bilong CF 2016. Description of three new species of Quadriacanthus (Monogenea: Ancyrocephalidae) gill parasites of Clarias submargi-

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